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itemprop="dateCreated datePublished" title="创建时间:2022-12-04 20:36:54" datetime=2022-12-04T20:36:54+08:00>2022-12-04</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-folder"></i> </span><span class=post-meta-item-text>分类于</span> <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/ itemprop=url rel=index><span itemprop=name>Java</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/Mybatis/ itemprop=url rel=index><span itemprop=name>Mybatis</span></a> </span></span><span class="post-meta-item cloudflare-page-counter" data-increment=true data-path=/2022/12/04/mybatis%E6%98%AF%E5%A6%82%E4%BD%95%E5%88%9D%E5%A7%8B%E5%8C%96mapper%E7%9A%84/ data-title=mybatis系列-mybatis是如何初始化mapper的 title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数:</span> <span class=cloudflare-page-counter-count></span></span></div><div class=post-description>前一篇讲了mybatis的初始化使用,如果我第一次看到这个使用入门文档,比较会产生疑惑的是配置了mapper,怎么就能通过selectOne跟语句id就能执行sql了,那么第一个问题,就是mapper是怎么被解析的,存在哪里,怎么被拿出来的</div></div></header><div class=post-body itemprop=articleBody><p>前一篇讲了mybatis的初始化使用,如果我第一次看到这个使用入门文档,比较会产生疑惑的是配置了mapper,怎么就能通过<code>selectOne</code>跟语句id就能执行sql了,那么第一个问题,就是mapper是怎么被解析的,存在哪里,怎么被拿出来的<h2 id=添加解析mapper><a class=headerlink href=#添加解析mapper title=添加解析mapper></a>添加解析mapper</h2><figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br></pre><td class=code><pre><span class=line>org.apache.ibatis.session.SqlSessionFactoryBuilder#build(java.io.InputStream)</span><br><span class=line><span class=keyword>public</span> SqlSessionFactory <span class="title function_">build</span><span class=params>(InputStream inputStream)</span> {</span><br><span class=line> <span class=keyword>return</span> build(inputStream, <span class=literal>null</span>, <span class=literal>null</span>);</span><br><span class=line>}</span><br></pre></table></figure><p>通过读取mybatis-config.xml来构建SqlSessionFactory,<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> SqlSessionFactory <span class="title function_">build</span><span class=params>(InputStream inputStream, String environment, Properties properties)</span> {</span><br><span class=line> <span class=keyword>try</span> {</span><br><span class=line> <span class=comment>// 创建下xml的解析器</span></span><br><span class=line> <span class=type>XMLConfigBuilder</span> <span class=variable>parser</span> <span class=operator>=</span> <span class=keyword>new</span> <span class="title class_">XMLConfigBuilder</span>(inputStream, environment, properties);</span><br><span class=line> <span class=comment>// 进行解析,后再构建</span></span><br><span class=line> <span class=keyword>return</span> build(parser.parse());</span><br><span class=line> } <span class=keyword>catch</span> (Exception e) {</span><br><span class=line> <span class=keyword>throw</span> ExceptionFactory.wrapException(<span class=string>"Error building SqlSession."</span>, e);</span><br><span class=line> } <span class=keyword>finally</span> {</span><br><span class=line> ErrorContext.instance().reset();</span><br><span class=line> <span class=keyword>try</span> {</span><br><span class=line> <span class=keyword>if</span> (inputStream != <span class=literal>null</span>) {</span><br><span class=line> inputStream.close();</span><br><span class=line> }</span><br><span class=line> } <span class=keyword>catch</span> (IOException e) {</span><br><span class=line> <span class=comment>// Intentionally ignore. Prefer previous error.</span></span><br><span class=line> }</span><br><span class=line> }</span><br></pre></table></figure><p>创建XMLConfigBuilder<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> <span class="title function_">XMLConfigBuilder</span><span class=params>(InputStream inputStream, String environment, Properties props)</span> {</span><br><span class=line> <span class=comment>// --------> 创建 XPathParser</span></span><br><span class=line> <span class=built_in>this</span>(<span class=keyword>new</span> <span class="title class_">XPathParser</span>(inputStream, <span class=literal>true</span>, props, <span class=keyword>new</span> <span class="title class_">XMLMapperEntityResolver</span>()), environment, props);</span><br><span class=line>}</span><br><span class=line></span><br><span class=line><span class=keyword>public</span> <span class="title function_">XPathParser</span><span class=params>(InputStream inputStream, <span class=type>boolean</span> validation, Properties variables, EntityResolver entityResolver)</span> {</span><br><span class=line> commonConstructor(validation, variables, entityResolver);</span><br><span class=line> <span class=built_in>this</span>.document = createDocument(<span class=keyword>new</span> <span class="title class_">InputSource</span>(inputStream));</span><br><span class=line> }</span><br><span class=line></span><br><span class=line><span class=keyword>private</span> <span class="title function_">XMLConfigBuilder</span><span class=params>(XPathParser parser, String environment, Properties props)</span> {</span><br><span class=line> <span class=built_in>super</span>(<span class=keyword>new</span> <span class="title class_">Configuration</span>());</span><br><span class=line> ErrorContext.instance().resource(<span class=string>"SQL Mapper Configuration"</span>);</span><br><span class=line> <span class=built_in>this</span>.configuration.setVariables(props);</span><br><span class=line> <span class=built_in>this</span>.parsed = <span class=literal>false</span>;</span><br><span class=line> <span class=built_in>this</span>.environment = environment;</span><br><span class=line> <span class=built_in>this</span>.parser = parser;</span><br><span class=line>}</span><br></pre></table></figure><p>这里主要是创建了Builder包含了Parser<br>然后调用parse方法<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> Configuration <span class="title function_">parse</span><span class=params>()</span> {</span><br><span class=line> <span class=keyword>if</span> (parsed) {</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">BuilderException</span>(<span class=string>"Each XMLConfigBuilder can only be used once."</span>);</span><br><span class=line> }</span><br><span class=line> <span class=comment>// 标记下是否已解析,但是这里是否有线程安全问题</span></span><br><span class=line> parsed = <span class=literal>true</span>;</span><br><span class=line> <span class=comment>// --------> 解析配置</span></span><br><span class=line> parseConfiguration(parser.evalNode(<span class=string>"/configuration"</span>));</span><br><span class=line> <span class=keyword>return</span> configuration;</span><br><span class=line>}</span><br></pre></table></figure><p>实际的解析区分了各类标签<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br></pre><td class=code><pre><span class=line><span class=keyword>private</span> <span class=keyword>void</span> <span class="title function_">parseConfiguration</span><span class=params>(XNode root)</span> {</span><br><span class=line> <span class=keyword>try</span> {</span><br><span class=line> <span class=comment>// issue #117 read properties first</span></span><br><span class=line> <span class=comment>// 解析properties,这个不是spring自带的,需要额外配置,并且在config文件里应该放在最前</span></span><br><span class=line> propertiesElement(root.evalNode(<span class=string>"properties"</span>));</span><br><span class=line> <span class=type>Properties</span> <span class=variable>settings</span> <span class=operator>=</span> settingsAsProperties(root.evalNode(<span class=string>"settings"</span>));</span><br><span class=line> loadCustomVfs(settings);</span><br><span class=line> loadCustomLogImpl(settings);</span><br><span class=line> typeAliasesElement(root.evalNode(<span class=string>"typeAliases"</span>));</span><br><span class=line> pluginElement(root.evalNode(<span class=string>"plugins"</span>));</span><br><span class=line> objectFactoryElement(root.evalNode(<span class=string>"objectFactory"</span>));</span><br><span class=line> objectWrapperFactoryElement(root.evalNode(<span class=string>"objectWrapperFactory"</span>));</span><br><span class=line> reflectorFactoryElement(root.evalNode(<span class=string>"reflectorFactory"</span>));</span><br><span class=line> settingsElement(settings);</span><br><span class=line> <span class=comment>// read it after objectFactory and objectWrapperFactory issue #631</span></span><br><span class=line> environmentsElement(root.evalNode(<span class=string>"environments"</span>));</span><br><span class=line> databaseIdProviderElement(root.evalNode(<span class=string>"databaseIdProvider"</span>));</span><br><span class=line> typeHandlerElement(root.evalNode(<span class=string>"typeHandlers"</span>));</span><br><span class=line> <span class=comment>// ----------> 我们需要关注的是mapper的处理</span></span><br><span class=line> mapperElement(root.evalNode(<span class=string>"mappers"</span>));</span><br><span class=line> } <span class=keyword>catch</span> (Exception e) {</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">BuilderException</span>(<span class=string>"Error parsing SQL Mapper Configuration. Cause: "</span> + e, e);</span><br><span class=line> }</span><br><span class=line>}</span><br></pre></table></figure><p>然后就是调用到mapperElement方法了<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br></pre><td class=code><pre><span class=line><span class=keyword>private</span> <span class=keyword>void</span> <span class="title function_">mapperElement</span><span class=params>(XNode parent)</span> <span class=keyword>throws</span> Exception {</span><br><span class=line> <span class=keyword>if</span> (parent != <span class=literal>null</span>) {</span><br><span class=line> <span class=keyword>for</span> (XNode child : parent.getChildren()) {</span><br><span class=line> <span class=keyword>if</span> (<span class=string>"package"</span>.equals(child.getName())) {</span><br><span class=line> <span class=type>String</span> <span class=variable>mapperPackage</span> <span class=operator>=</span> child.getStringAttribute(<span class=string>"name"</span>);</span><br><span class=line> configuration.addMappers(mapperPackage);</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> <span class=type>String</span> <span class=variable>resource</span> <span class=operator>=</span> child.getStringAttribute(<span class=string>"resource"</span>);</span><br><span class=line> <span class=type>String</span> <span class=variable>url</span> <span class=operator>=</span> child.getStringAttribute(<span class=string>"url"</span>);</span><br><span class=line> <span class=type>String</span> <span class=variable>mapperClass</span> <span class=operator>=</span> child.getStringAttribute(<span class=string>"class"</span>);</span><br><span class=line> <span class=keyword>if</span> (resource != <span class=literal>null</span> && url == <span class=literal>null</span> && mapperClass == <span class=literal>null</span>) {</span><br><span class=line> ErrorContext.instance().resource(resource);</span><br><span class=line> <span class=keyword>try</span>(<span class=type>InputStream</span> <span class=variable>inputStream</span> <span class=operator>=</span> Resources.getResourceAsStream(resource)) {</span><br><span class=line> <span class=type>XMLMapperBuilder</span> <span class=variable>mapperParser</span> <span class=operator>=</span> <span class=keyword>new</span> <span class="title class_">XMLMapperBuilder</span>(inputStream, configuration, resource, configuration.getSqlFragments());</span><br><span class=line> <span class=comment>// --------> 我们这没有指定package,所以是走到这</span></span><br><span class=line> mapperParser.parse();</span><br><span class=line> }</span><br><span class=line> } <span class=keyword>else</span> <span class=keyword>if</span> (resource == <span class=literal>null</span> && url != <span class=literal>null</span> && mapperClass == <span class=literal>null</span>) {</span><br><span class=line> ErrorContext.instance().resource(url);</span><br><span class=line> <span class=keyword>try</span>(<span class=type>InputStream</span> <span class=variable>inputStream</span> <span class=operator>=</span> Resources.getUrlAsStream(url)){</span><br><span class=line> <span class=type>XMLMapperBuilder</span> <span class=variable>mapperParser</span> <span class=operator>=</span> <span class=keyword>new</span> <span class="title class_">XMLMapperBuilder</span>(inputStream, configuration, url, configuration.getSqlFragments());</span><br><span class=line> mapperParser.parse();</span><br><span class=line> }</span><br><span class=line> } <span class=keyword>else</span> <span class=keyword>if</span> (resource == <span class=literal>null</span> && url == <span class=literal>null</span> && mapperClass != <span class=literal>null</span>) {</span><br><span class=line> Class<?> mapperInterface = Resources.classForName(mapperClass);</span><br><span class=line> configuration.addMapper(mapperInterface);</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">BuilderException</span>(<span class=string>"A mapper element may only specify a url, resource or class, but not more than one."</span>);</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line>}</span><br></pre></table></figure><p>核心就在这个parse()方法<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> <span class=keyword>void</span> <span class="title function_">parse</span><span class=params>()</span> {</span><br><span class=line> <span class=keyword>if</span> (!configuration.isResourceLoaded(resource)) {</span><br><span class=line> <span class=comment>// -------> 然后就是走到这里,配置xml的mapper节点的内容</span></span><br><span class=line> configurationElement(parser.evalNode(<span class=string>"/mapper"</span>));</span><br><span class=line> configuration.addLoadedResource(resource);</span><br><span class=line> bindMapperForNamespace();</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> parsePendingResultMaps();</span><br><span class=line> parsePendingCacheRefs();</span><br><span class=line> parsePendingStatements();</span><br><span class=line>}</span><br></pre></table></figure><p>具体的处理逻辑<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br></pre><td class=code><pre><span class=line><span class=keyword>private</span> <span class=keyword>void</span> <span class="title function_">configurationElement</span><span class=params>(XNode context)</span> {</span><br><span class=line> <span class=keyword>try</span> {</span><br><span class=line> <span class=type>String</span> <span class=variable>namespace</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"namespace"</span>);</span><br><span class=line> <span class=keyword>if</span> (namespace == <span class=literal>null</span> || namespace.isEmpty()) {</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">BuilderException</span>(<span class=string>"Mapper's namespace cannot be empty"</span>);</span><br><span class=line> }</span><br><span class=line> builderAssistant.setCurrentNamespace(namespace);</span><br><span class=line> cacheRefElement(context.evalNode(<span class=string>"cache-ref"</span>));</span><br><span class=line> cacheElement(context.evalNode(<span class=string>"cache"</span>));</span><br><span class=line> parameterMapElement(context.evalNodes(<span class=string>"/mapper/parameterMap"</span>));</span><br><span class=line> resultMapElements(context.evalNodes(<span class=string>"/mapper/resultMap"</span>));</span><br><span class=line> sqlElement(context.evalNodes(<span class=string>"/mapper/sql"</span>));</span><br><span class=line> <span class=comment>// -------> 走到这,从上下文构建statement</span></span><br><span class=line> buildStatementFromContext(context.evalNodes(<span class=string>"select|insert|update|delete"</span>));</span><br><span class=line> } <span class=keyword>catch</span> (Exception e) {</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">BuilderException</span>(<span class=string>"Error parsing Mapper XML. The XML location is '"</span> + resource + <span class=string>"'. Cause: "</span> + e, e);</span><br><span class=line> }</span><br><span class=line>}</span><br></pre></table></figure><p>具体代码在这,从上下文构建<code>statement</code>,只不过区分了下<code>databaseId</code><figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br></pre><td class=code><pre><span class=line><span class=keyword>private</span> <span class=keyword>void</span> <span class="title function_">buildStatementFromContext</span><span class=params>(List<XNode> list)</span> {</span><br><span class=line> <span class=keyword>if</span> (configuration.getDatabaseId() != <span class=literal>null</span>) {</span><br><span class=line> buildStatementFromContext(list, configuration.getDatabaseId());</span><br><span class=line> }</span><br><span class=line> <span class=comment>// -----> 判断databaseId</span></span><br><span class=line> buildStatementFromContext(list, <span class=literal>null</span>);</span><br><span class=line>}</span><br></pre></table></figure><p>判断下<code>databaseId</code><figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br></pre><td class=code><pre><span class=line><span class=keyword>private</span> <span class=keyword>void</span> <span class="title function_">buildStatementFromContext</span><span class=params>(List<XNode> list, String requiredDatabaseId)</span> {</span><br><span class=line> <span class=keyword>for</span> (XNode context : list) {</span><br><span class=line> <span class=keyword>final</span> <span class=type>XMLStatementBuilder</span> <span class=variable>statementParser</span> <span class=operator>=</span> <span class=keyword>new</span> <span class="title class_">XMLStatementBuilder</span>(configuration, builderAssistant, context, requiredDatabaseId);</span><br><span class=line> <span class=keyword>try</span> {</span><br><span class=line> <span class=comment>// -------> 解析statement节点</span></span><br><span class=line> statementParser.parseStatementNode();</span><br><span class=line> } <span class=keyword>catch</span> (IncompleteElementException e) {</span><br><span class=line> configuration.addIncompleteStatement(statementParser);</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line>}</span><br></pre></table></figure><p>接下来就是真正处理的xml语句内容的,各个节点的信息内容<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br><span class=line>44</span><br><span class=line>45</span><br><span class=line>46</span><br><span class=line>47</span><br><span class=line>48</span><br><span class=line>49</span><br><span class=line>50</span><br><span class=line>51</span><br><span class=line>52</span><br><span class=line>53</span><br><span class=line>54</span><br><span class=line>55</span><br><span class=line>56</span><br><span class=line>57</span><br><span class=line>58</span><br><span class=line>59</span><br><span class=line>60</span><br><span class=line>61</span><br><span class=line>62</span><br><span class=line>63</span><br><span class=line>64</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> <span class=keyword>void</span> <span class="title function_">parseStatementNode</span><span class=params>()</span> {</span><br><span class=line> <span class=type>String</span> <span class=variable>id</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"id"</span>);</span><br><span class=line> <span class=type>String</span> <span class=variable>databaseId</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"databaseId"</span>);</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (!databaseIdMatchesCurrent(id, databaseId, <span class=built_in>this</span>.requiredDatabaseId)) {</span><br><span class=line> <span class=keyword>return</span>;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=type>String</span> <span class=variable>nodeName</span> <span class=operator>=</span> context.getNode().getNodeName();</span><br><span class=line> <span class=type>SqlCommandType</span> <span class=variable>sqlCommandType</span> <span class=operator>=</span> SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));</span><br><span class=line> <span class=type>boolean</span> <span class=variable>isSelect</span> <span class=operator>=</span> sqlCommandType == SqlCommandType.SELECT;</span><br><span class=line> <span class=type>boolean</span> <span class=variable>flushCache</span> <span class=operator>=</span> context.getBooleanAttribute(<span class=string>"flushCache"</span>, !isSelect);</span><br><span class=line> <span class=type>boolean</span> <span class=variable>useCache</span> <span class=operator>=</span> context.getBooleanAttribute(<span class=string>"useCache"</span>, isSelect);</span><br><span class=line> <span class=type>boolean</span> <span class=variable>resultOrdered</span> <span class=operator>=</span> context.getBooleanAttribute(<span class=string>"resultOrdered"</span>, <span class=literal>false</span>);</span><br><span class=line></span><br><span class=line> <span class=comment>// Include Fragments before parsing</span></span><br><span class=line> <span class=type>XMLIncludeTransformer</span> <span class=variable>includeParser</span> <span class=operator>=</span> <span class=keyword>new</span> <span class="title class_">XMLIncludeTransformer</span>(configuration, builderAssistant);</span><br><span class=line> includeParser.applyIncludes(context.getNode());</span><br><span class=line></span><br><span class=line> <span class=type>String</span> <span class=variable>parameterType</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"parameterType"</span>);</span><br><span class=line> Class<?> parameterTypeClass = resolveClass(parameterType);</span><br><span class=line></span><br><span class=line> <span class=type>String</span> <span class=variable>lang</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"lang"</span>);</span><br><span class=line> <span class=type>LanguageDriver</span> <span class=variable>langDriver</span> <span class=operator>=</span> getLanguageDriver(lang);</span><br><span class=line></span><br><span class=line> <span class=comment>// Parse selectKey after includes and remove them.</span></span><br><span class=line> processSelectKeyNodes(id, parameterTypeClass, langDriver);</span><br><span class=line></span><br><span class=line> <span class=comment>// Parse the SQL (pre: <selectKey> and <include> were parsed and removed)</span></span><br><span class=line> KeyGenerator keyGenerator;</span><br><span class=line> <span class=type>String</span> <span class=variable>keyStatementId</span> <span class=operator>=</span> id + SelectKeyGenerator.SELECT_KEY_SUFFIX;</span><br><span class=line> keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, <span class=literal>true</span>);</span><br><span class=line> <span class=keyword>if</span> (configuration.hasKeyGenerator(keyStatementId)) {</span><br><span class=line> keyGenerator = configuration.getKeyGenerator(keyStatementId);</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> keyGenerator = context.getBooleanAttribute(<span class=string>"useGeneratedKeys"</span>,</span><br><span class=line> configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))</span><br><span class=line> ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>// 语句的主要参数解析</span></span><br><span class=line> <span class=type>SqlSource</span> <span class=variable>sqlSource</span> <span class=operator>=</span> langDriver.createSqlSource(configuration, context, parameterTypeClass);</span><br><span class=line> <span class=type>StatementType</span> <span class=variable>statementType</span> <span class=operator>=</span> StatementType.valueOf(context.getStringAttribute(<span class=string>"statementType"</span>, StatementType.PREPARED.toString()));</span><br><span class=line> <span class=type>Integer</span> <span class=variable>fetchSize</span> <span class=operator>=</span> context.getIntAttribute(<span class=string>"fetchSize"</span>);</span><br><span class=line> <span class=type>Integer</span> <span class=variable>timeout</span> <span class=operator>=</span> context.getIntAttribute(<span class=string>"timeout"</span>);</span><br><span class=line> <span class=type>String</span> <span class=variable>parameterMap</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"parameterMap"</span>);</span><br><span class=line> <span class=type>String</span> <span class=variable>resultType</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"resultType"</span>);</span><br><span class=line> Class<?> resultTypeClass = resolveClass(resultType);</span><br><span class=line> <span class=type>String</span> <span class=variable>resultMap</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"resultMap"</span>);</span><br><span class=line> <span class=type>String</span> <span class=variable>resultSetType</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"resultSetType"</span>);</span><br><span class=line> <span class=type>ResultSetType</span> <span class=variable>resultSetTypeEnum</span> <span class=operator>=</span> resolveResultSetType(resultSetType);</span><br><span class=line> <span class=keyword>if</span> (resultSetTypeEnum == <span class=literal>null</span>) {</span><br><span class=line> resultSetTypeEnum = configuration.getDefaultResultSetType();</span><br><span class=line> }</span><br><span class=line> <span class=type>String</span> <span class=variable>keyProperty</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"keyProperty"</span>);</span><br><span class=line> <span class=type>String</span> <span class=variable>keyColumn</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"keyColumn"</span>);</span><br><span class=line> <span class=type>String</span> <span class=variable>resultSets</span> <span class=operator>=</span> context.getStringAttribute(<span class=string>"resultSets"</span>);</span><br><span class=line></span><br><span class=line> <span class=comment>// --------> 添加映射的statement</span></span><br><span class=line> builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,</span><br><span class=line> fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,</span><br><span class=line> resultSetTypeEnum, flushCache, useCache, resultOrdered,</span><br><span class=line> keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);</span><br><span class=line>}</span><br></pre></table></figure><p>添加的逻辑具体可以看下<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br><span class=line>44</span><br><span class=line>45</span><br><span class=line>46</span><br><span class=line>47</span><br><span class=line>48</span><br><span class=line>49</span><br><span class=line>50</span><br><span class=line>51</span><br><span class=line>52</span><br><span class=line>53</span><br><span class=line>54</span><br><span class=line>55</span><br><span class=line>56</span><br><span class=line>57</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> MappedStatement <span class="title function_">addMappedStatement</span><span class=params>(</span></span><br><span class=line><span class=params> String id,</span></span><br><span class=line><span class=params> SqlSource sqlSource,</span></span><br><span class=line><span class=params> StatementType statementType,</span></span><br><span class=line><span class=params> SqlCommandType sqlCommandType,</span></span><br><span class=line><span class=params> Integer fetchSize,</span></span><br><span class=line><span class=params> Integer timeout,</span></span><br><span class=line><span class=params> String parameterMap,</span></span><br><span class=line><span class=params> Class<?> parameterType,</span></span><br><span class=line><span class=params> String resultMap,</span></span><br><span class=line><span class=params> Class<?> resultType,</span></span><br><span class=line><span class=params> ResultSetType resultSetType,</span></span><br><span class=line><span class=params> <span class=type>boolean</span> flushCache,</span></span><br><span class=line><span class=params> <span class=type>boolean</span> useCache,</span></span><br><span class=line><span class=params> <span class=type>boolean</span> resultOrdered,</span></span><br><span class=line><span class=params> KeyGenerator keyGenerator,</span></span><br><span class=line><span class=params> String keyProperty,</span></span><br><span class=line><span class=params> String keyColumn,</span></span><br><span class=line><span class=params> String databaseId,</span></span><br><span class=line><span class=params> LanguageDriver lang,</span></span><br><span class=line><span class=params> String resultSets)</span> {</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (unresolvedCacheRef) {</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">IncompleteElementException</span>(<span class=string>"Cache-ref not yet resolved"</span>);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> id = applyCurrentNamespace(id, <span class=literal>false</span>);</span><br><span class=line> <span class=type>boolean</span> <span class=variable>isSelect</span> <span class=operator>=</span> sqlCommandType == SqlCommandType.SELECT;</span><br><span class=line></span><br><span class=line> MappedStatement.<span class=type>Builder</span> <span class=variable>statementBuilder</span> <span class=operator>=</span> <span class=keyword>new</span> <span class="title class_">MappedStatement</span>.Builder(configuration, id, sqlSource, sqlCommandType)</span><br><span class=line> .resource(resource)</span><br><span class=line> .fetchSize(fetchSize)</span><br><span class=line> .timeout(timeout)</span><br><span class=line> .statementType(statementType)</span><br><span class=line> .keyGenerator(keyGenerator)</span><br><span class=line> .keyProperty(keyProperty)</span><br><span class=line> .keyColumn(keyColumn)</span><br><span class=line> .databaseId(databaseId)</span><br><span class=line> .lang(lang)</span><br><span class=line> .resultOrdered(resultOrdered)</span><br><span class=line> .resultSets(resultSets)</span><br><span class=line> .resultMaps(getStatementResultMaps(resultMap, resultType, id))</span><br><span class=line> .resultSetType(resultSetType)</span><br><span class=line> .flushCacheRequired(valueOrDefault(flushCache, !isSelect))</span><br><span class=line> .useCache(valueOrDefault(useCache, isSelect))</span><br><span class=line> .cache(currentCache);</span><br><span class=line></span><br><span class=line> <span class=type>ParameterMap</span> <span class=variable>statementParameterMap</span> <span class=operator>=</span> getStatementParameterMap(parameterMap, parameterType, id);</span><br><span class=line> <span class=keyword>if</span> (statementParameterMap != <span class=literal>null</span>) {</span><br><span class=line> statementBuilder.parameterMap(statementParameterMap);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=type>MappedStatement</span> <span class=variable>statement</span> <span class=operator>=</span> statementBuilder.build();</span><br><span class=line> <span class=comment>// ------> 正好是这里在configuration中添加了映射好的statement</span></span><br><span class=line> configuration.addMappedStatement(statement);</span><br><span class=line> <span class=keyword>return</span> statement;</span><br><span class=line>}</span><br></pre></table></figure><p>而里面就是往map里添加<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> <span class=keyword>void</span> <span class="title function_">addMappedStatement</span><span class=params>(MappedStatement ms)</span> {</span><br><span class=line> mappedStatements.put(ms.getId(), ms);</span><br><span class=line>}</span><br></pre></table></figure><h2 id=获取mapper><a class=headerlink href=#获取mapper title=获取mapper></a>获取mapper</h2><figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br></pre><td class=code><pre><span class=line><span class=type>StudentDO</span> <span class=variable>studentDO</span> <span class=operator>=</span> session.selectOne(<span class=string>"com.nicksxs.mybatisdemo.StudentMapper.selectStudent"</span>, <span class=number>1</span>);</span><br></pre></table></figure><p>就是调用了 <code>org.apache.ibatis.session.defaults.DefaultSqlSession#selectOne(java.lang.String, java.lang.Object)</code><figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> <T> T <span class="title function_">selectOne</span><span class=params>(String statement, Object parameter)</span> {</span><br><span class=line> <span class=comment>// Popular vote was to return null on 0 results and throw exception on too many.</span></span><br><span class=line> List<T> list = <span class=built_in>this</span>.selectList(statement, parameter);</span><br><span class=line> <span class=keyword>if</span> (list.size() == <span class=number>1</span>) {</span><br><span class=line> <span class=keyword>return</span> list.get(<span class=number>0</span>);</span><br><span class=line> } <span class=keyword>else</span> <span class=keyword>if</span> (list.size() > <span class=number>1</span>) {</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">TooManyResultsException</span>(<span class=string>"Expected one result (or null) to be returned by selectOne(), but found: "</span> + list.size());</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> <span class=keyword>return</span> <span class=literal>null</span>;</span><br><span class=line> }</span><br><span class=line>}</span><br></pre></table></figure><p>调用实际的实现方法<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> <E> List<E> <span class="title function_">selectList</span><span class=params>(String statement, Object parameter)</span> {</span><br><span class=line> <span class=keyword>return</span> <span class=built_in>this</span>.selectList(statement, parameter, RowBounds.DEFAULT);</span><br><span class=line>}</span><br></pre></table></figure><p>这里还有一层<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> <E> List<E> <span class="title function_">selectList</span><span class=params>(String statement, Object parameter, RowBounds rowBounds)</span> {</span><br><span class=line> <span class=keyword>return</span> selectList(statement, parameter, rowBounds, Executor.NO_RESULT_HANDLER);</span><br><span class=line>}</span><br></pre></table></figure><p>根本的就是从configuration里获取了mappedStatement<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br></pre><td class=code><pre><span class=line><span class=keyword>private</span> <E> List<E> <span class="title function_">selectList</span><span class=params>(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler)</span> {</span><br><span class=line> <span class=keyword>try</span> {</span><br><span class=line> <span class=comment>// 这里进行了获取</span></span><br><span class=line> <span class=type>MappedStatement</span> <span class=variable>ms</span> <span class=operator>=</span> configuration.getMappedStatement(statement);</span><br><span class=line> <span class=keyword>return</span> executor.query(ms, wrapCollection(parameter), rowBounds, handler);</span><br><span class=line> } <span class=keyword>catch</span> (Exception e) {</span><br><span class=line> <span class=keyword>throw</span> ExceptionFactory.wrapException(<span class=string>"Error querying database. Cause: "</span> + e, e);</span><br><span class=line> } <span class=keyword>finally</span> {</span><br><span class=line> ErrorContext.instance().reset();</span><br><span class=line> }</span><br><span class=line>}</span><br></pre></table></figure></div><footer class=post-footer><div class="affiliate-creative affiliate-creative--post-end" data-affiliate-id=tencent-cloud-general><a rel="sponsored noopener" aria-label=腾讯云产品优惠 href=https://cloud.tencent.com/act/cps/redirect?redirect=2446&cps_key=2e33a1eedb380997d03618b4a5ba6ca7&from=console target=_blank><img alt=腾讯云服务器、数据库和云产品优惠 decoding=async height=419 loading=lazy src=/uploads/affiliate/tencent-cloud-general.webp width=690> </a><span class=affiliate-disclosure>推广</span></div><div class=reward-container><div>请我一杯咖啡吧!</div><button>赞赏</button><div class=post-reward><div><img alt="Nicksxs 微信" src=https://i.loli.net/2020/01/12/NUlWanT31E8LQGx.png><span>微信</span></div><div><img alt="Nicksxs 支付宝" src=https://ooo.0o0.ooo/2016/08/17/57b421e773057.jpg><span>支付宝</span></div></div></div><div class=post-copyright><ul><li class=post-copyright-author><strong>本文作者: </strong>Nicksxs<li class=post-copyright-link><strong>本文链接:</strong> <a href=https://nicksxs.me/2022/12/04/mybatis%E6%98%AF%E5%A6%82%E4%BD%95%E5%88%9D%E5%A7%8B%E5%8C%96mapper%E7%9A%84/ title=mybatis系列-mybatis是如何初始化mapper的>https://nicksxs.me/2022/12/04/mybatis是如何初始化mapper的/</a><li class=post-copyright-license><strong>版权声明: </strong>本博客所有文章除特别声明外,均采用 <a href=https://creativecommons.org/licenses/by-nc-sa/4.0/ rel=noopener target=_blank><i class="fab fa-fw fa-creative-commons"></i>BY-NC-SA</a> 许可协议。转载请注明出处!</ul></div><div class=post-tags><a href=/tags/Java/ rel=tag># Java</a><a href=/tags/MySQL/ rel=tag># MySQL</a><a href=/tags/Mybatis/ rel=tag># Mybatis</a></div><div class=post-nav><div class=post-nav-item><a href=/2022/11/27/mybatis%E7%B3%BB%E5%88%97-%E5%85%A5%E9%97%A8%E7%AF%87/ rel=prev title=mybatis系列-入门篇><i class="fa fa-angle-left"></i> mybatis系列-入门篇</a></div><div class=post-nav-item><a href=/2022/12/11/mybatis%E7%B3%BB%E5%88%97-%E7%AC%AC%E4%B8%80%E6%9D%A1sql%E7%9A%84%E7%BB%86%E8%8A%82/ rel=next title=mybatis系列-第一条sql的细节>mybatis系列-第一条sql的细节 <i class="fa fa-angle-right"></i></a></div></div></footer></article></div><div class=comments id=disqus_thread><noscript>Please enable JavaScript to view the comments powered by Disqus.</noscript></div></div></main><footer class=footer><div class=footer-inner><div class=beian><a href=https://beian.miit.gov.cn/ rel=noopener target=_blank>浙ICP备16002580号-2 </a><img alt src=/uploads/beian.png><a href=https://beian.mps.gov.cn/#/query/webSearch?code=33010602011094 rel=noopener target=_blank>浙公网安备 33010602011094号</a></div><div class=copyright>© <span itemprop=copyrightYear>2026</span><span class=with-love><i class="fa fa-heart"></i> </span><span class=author itemprop=copyrightHolder>Nicksxs</span></div></div></footer><div class="toggle sidebar-toggle" role=button><span class=toggle-line></span><span class=toggle-line></span><span class=toggle-line></span></div><div class=sidebar-dimmer></div><div aria-label=返回顶部 class=back-to-top role=button><i class="fa fa-arrow-up fa-lg"></i><span>0%</span></div><a aria-label="在 GitHub 上关注我" title="在 GitHub 上关注我" class=github-corner href=https://github.com/nicksxs rel=noopener target=_blank><svg viewbox="0 0 250 250" aria-hidden=true height=80 width=80><path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path><path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2" style="transform-origin:130px 106px" class=octo-arm fill=currentColor></path><path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z" class=octo-body fill=currentColor></path></svg></a><noscript><div class=noscript-warning>Theme NexT works best with JavaScript enabled</div></noscript><script data-cloudflare-page-counter-config type=application/json>{"enable":true,"endpoint":"https://counter.nicksxs.me","site":"nicksxs","local_cache":true,"timeout":5000,"icon":"far fa-eye","item_text":true}</script><script src=/js/cloudflare-page-counter.js></script><script class=next-config data-name=disqus type=application/json>{"enable":true,"shortname":"nicksxs","count":false,"i18n":{"disqus":"disqus"}}</script><script defer src=/js/third-party/comments/disqus.js></script>
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