MyBatis插件

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已于 2024-04-03 20:32:03 修改

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分类专栏： Java学习笔记文章标签： mybatis

于 2024-04-03 12:45:45 首次发布

本文链接：https://blog.youkuaiyun.com/Demo_00/article/details/137341047

本文详细解释了MyBatis插件的工作原理，包括插件的注册过程、在Configuration类中的应用、如何生成拦截代理类以及执行拦截的机制，重点介绍了Interceptor、InterceptorChain和Plugin类的关键方法和功能。

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MyBatis插件

Mybatis插件原理

1. 注册插件（解析SqlMapConfig.xml时）

//XMLConfigBuilder类的parseConfiguration方法
private void parseConfiguration(XNode root) {
   
    try {
   
      // issue #117 read properties first
      propertiesElement(root.evalNode("properties"));
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      loadCustomVfs(settings);
      loadCustomLogImpl(settings);
      typeAliasesElement(root.evalNode("typeAliases"));
      //解析插件  
      pluginElement(root.evalNode("plugins"));
      objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      reflectorFactoryElement(root.evalNode("reflectorFactory"));
      settingsElement(settings);
      // read it after objectFactory and objectWrapperFactory issue #631
      environmentsElement(root.evalNode("environments"));
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      typeHandlerElement(root.evalNode("typeHandlers"));
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
   
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }

  private void pluginElement(XNode parent) throws Exception {
   
    if (parent != null) {
   
      for (XNode child : parent.getChildren()) {
   
        String interceptor = child.getStringAttribute("interceptor");
        Properties properties = child.getChildrenAsProperties();
        Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).getDeclaredConstructor().newInstance();
        interceptorInstance.setProperties(properties);
        //注册插件
        configuration.addInterceptor(interceptorInstance);
      }
    }
  }

  public void addInterceptor(Interceptor interceptor) {
   
    interceptorChain.addInterceptor(interceptor);
  }

public class InterceptorChain {
   
  //插件列表
  private final List<Interceptor> interceptors = new ArrayList<>();
  //应用插件
  public Object pluginAll(Object target) {
   
    for (Interceptor interceptor : interceptors) {
   
      target = interceptor.plugin(target);
    }
    return target;
  }
 //注册插件
  public void addInterceptor(Interceptor interceptor) {
   
    interceptors.add(interceptor);
  }

  public List<Interceptor> getInterceptors() {
   
    return Collections.unmodifiableList(interceptors);
  }

}

2. 应用插件

//Configuration类中
  public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
   
    ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
      //应用插件，拦截ParameterHandler
    parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
    return parameterHandler;
  }

  public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds, ParameterHandler parameterHandler,
      ResultHandler resultHandler, BoundSql boundSql) {
   
    ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds);
      //应用插件，拦截ResultSetHandler
    resultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);
    return