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前言

拦截器并不是简单对Dao层对象进行拦截，而是更加偏向底层的拦截，拦截的是Executor和各种Handler。

在这四个里边，最终要的是Executor和StatementHandler，当然最常用的是StatementHandler因为它是与数据库实际交互的，更加底层。
我们真正在StatementHandler开启的任务是拦截操作，拦截器的就是增删改查的处理，是通过StatementHandler其中的两个方法体现的，query和update方法

如果我们方法都要拦截，最好我们直接拦截prepare方法，因为他有两个好处，一个是prepare在update和query方法执行前执行，返回值是statement。另一个是prepare方法中的入参中有connection对象。所有JDBC的操作都是基于Connection，有了连接我们就有了一切。

一：拦截器获取拦截对象

答案是在intercepter方法当中：

@Intercepts({
        @Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})
})
public class MyMybatisInterceptor3 extends MyMybatisInterceptorAdapter {
    private static final Logger log = LoggerFactory.getLogger(MyMybatisInterceptor3.class);
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        if (log.isDebugEnabled())
            log.debug("-----this is myMybatisInterceptor3-------");
        MetaObject metaObject = SystemMetaObject.forObject(invocation);
        String methodName = (String) metaObject.getValue("method.name");
        String sql = (String) metaObject.getValue("target.delegate.boundSql.sql");
        if (log.isDebugEnabled())
            log.debug("methodname is " + methodName + " sql is " + sql);
        return invocation.proceed();
    }
    @Override
    public void setProperties(Properties properties) {

    }
}

Invocation 对象源码

public class Invocation {

  private final Object target;
  private final Method method;
  private final Object[] args;

  public Invocation(Object target, Method method, Object[] args) {
    this.target = target;
    this.method = method;
    this.args = args;
  }

  public Object getTarget() {
    return target;
  }

  public Method getMethod() {
    return method;
  }

  public Object[] getArgs() {
    return args;
  }

  public Object proceed() throws InvocationTargetException, IllegalAccessException {
    return method.invoke(target, args);
  }

}

Invocation对象里边有一个target对象，代表的就是拦截器所拦截的目标
method所代表的就是我们拦截的方法。当前案例中对饮的就是prepare方法
Object[] args这个数据，代表的就是拦截方法的参数。

1：如果获取被拦截方法和参数

在这里插入图片描述

2：演示证明

@Intercepts({
        @Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})
})

public class MyMybatisInterceptor3 extends MyMybatisInterceptorAdapter {

    private static final Logger log = LoggerFactory.getLogger(MyMybatisInterceptor3.class);

    @Override
    public Object intercept(Invocation invocation) throws Throwable {

        if (log.isDebugEnabled())
            log.debug("-----this is myMybatisInterceptor3-------");

        MetaObject metaObject = SystemMetaObject.forObject(invocation);

        String methodName = (String) metaObject.getValue("method.name");
        String sql = (String) metaObject.getValue("target.delegate.boundSql.sql");

        if (log.isDebugEnabled())
            log.debug("methodname is " + methodName + " sql is " + sql);

        return invocation.proceed();
    }

    @Override
    public void setProperties(Properties properties) {

    }
}

    <plugins>
        <plugin interceptor="com.baizhiedu.plugins.MyMybatisInterceptor3"/>
    </plugins>

在这里插入图片描述

二：MetaObject

1：MetaObject简介

Mybatis封装的反射，进行导航式的数据取值与赋值。整个过程都是基于反射完成，十分简化开发。

        MetaObject metaObject = SystemMetaObject.forObject(invocation);
        String methodName = (String) metaObject.getValue("method.name");
        String sql = (String) metaObject.getValue("target.delegate.boundSql.sql");
        log.debug("methodname is " + methodName + " sql is " + sql);

2：MetaObject代码展示

package org.apache.ibatis.reflection;

public class MetaObject {

  private final Object originalObject;
  private final ObjectWrapper objectWrapper;
  private final ObjectFactory objectFactory;
  private final ObjectWrapperFactory objectWrapperFactory;
  private final ReflectorFactory reflectorFactory;

  private MetaObject(Object object, ObjectFactory objectFactory, ObjectWrapperFactory objectWrapperFactory, ReflectorFactory reflectorFactory) {
    this.originalObject = object;
    this.objectFactory = objectFactory;
    this.objectWrapperFactory = objectWrapperFactory;
    this.reflectorFactory = reflectorFactory;

    if (object instanceof ObjectWrapper) {
      this.objectWrapper = (ObjectWrapper) object;
    } else if (objectWrapperFactory.hasWrapperFor(object)) {
      this.objectWrapper = objectWrapperFactory.getWrapperFor(this, object);
    } else if (object instanceof Map) {
      this.objectWrapper = new MapWrapper(this, (Map) object);
    } else if (object instanceof Collection) {
      this.objectWrapper = new CollectionWrapper(this, (Collection) object);
    } else {
      this.objectWrapper = new BeanWrapper(this, object);
    }
  }