Mybatis Plugin（拦截器）的开发

1.Plugin

MyBatis 允许使用插件来拦截的方法调用包括：

• Executor (update, query, flushStatements, commit, rollback,

getTransaction, close, isClosed)

• ParameterHandler (getParameterObject, setParameters)

• ResultSetHandler (handleResultSets, handleOutputParameters)

• StatementHandler (prepare, parameterize, batch, update, query)

注意;可以通过插件拦截到这四个对象，修改参数等操作：

你必须要知道的类:

1. org.apache.ibatis.plugin.Plugin
2. org.apache.ibatis.reflection.SystemMetaObject

2.使用步骤

1. 实现 Interceptor 接口
1. 三个方法执行顺序
1. setProperties()
2. plugin()
3. intercept()

 1 FirstIntercepter=====>setProperties
 2 FirstIntercepter====>[email protected]
 3 FirstIntercepter====>plu[email protected]2f0a87b3
 4 FirstIntercepter====>plu[email protected]4fcd19b3
 5 FirstIntercepter====>plu[email protected]2fd66ad3
 6 DEBUG 09-05 11:56:24,696 ==> Preparing: select * from employee where id=? (BaseJdbcLogger.java:159)
 7 FirstIntercepter:===>intercept
 8 DEBUG 09-05 11:56:24,722 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:159)
 9 DEBUG 09-05 11:56:24,739 <== Total: 1 (BaseJdbcLogger.java:159)
10 Employee [id=1, lastName=tom, gender=1, email[email protected], depid=null]

1. 给你的拦截器签名：

 1 /**
 2 * 完成插件签名：
 3 * 告诉MyBatis当前插件用来拦截哪个对象的哪个方法
 4 * type:要拦截的四大类型
 5 * method：拦截那个方法
 6 * args：这个方法的入参
 7 * */
 8 @Intercepts({
 9 @Signature(type=StatementHandler.class,
10 method="parameterize",
11 args=java.sql.Statement.class
12 )
13 })
14 public class FirstIntercepter implements Interceptor

1. mybatis-cfg.xml中配置插件
1. 这里注意配置plugins的标签顺序，以免出错，在environments上面

<!-- plugins 插件的配置 实际上是使用：intercepter原理代理的 -->
<plugins>
<plugin interceptor="mybatis.intercepter.FirstIntercepter">
<property name="param1" value="root"/>
<property name="param2" value="root"/>
</plugin>
</plugins>

3.多个插件的执行

1. 、多个插件依次生成目标对象的代理对象，层层包裹，先声明的先包裹；形成代理链
2. 、可以理解为:初始化执行
3. 执行log
4. FirstIntercepter=====>setProperties

 1 MySecondIntercepter====>setProperties:{param1=root}
 2 FirstIntercepter====>[email protected]
 3 MySecondIntercepter====>plugin:[email protected]
 4 FirstIntercepter====>plu[email protected]2f0a87b3
 5 MySecondIntercepter====>plugin:[email protected]a87b3
 6 FirstIntercepter====>plu[email protected]4fcd19b3
 7 MySecondIntercepter====>plugin:[email protected]d19b3
 8 FirstIntercepter====>plu[email protected]2fd66ad3
 9 MySecondIntercepter====>plugin:[email protected]66ad3
10 DEBUG 09-05 12:07:01,928 ==> Preparing: select * from employee where id=? (BaseJdbcLogger.java:159)
11 MySecondIntercepter====>intercept:public abstract void org.apache.ibatis.executor.statement.StatementHandler.parameterize(java.sql.Statement) throws java.sql.SQLException
12 FirstIntercepter:===>intercept
13 DEBUG 09-05 12:07:01,954 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:159)
14 DEBUG 09-05 12:07:01,968 <== Total: 1 (BaseJdbcLogger.java:159)
15 Employee [id=1, lastName=tom, gender=1, email[email protected], depid=null]

4.实现拦截修改参数

• sql

<!-- Employee getSelectEmp(Integer id); -->
<select id="getSelectEmp" parameterType="java.lang.Integer"
resultType="mybatis.bean.Employee">
select * from employee where id=#{id}
</select>

• 这里我们拦截id：

由于ibatis中参数的声明存在与 StatementHandler中所以注意签名

• 1 @Intercepts({
  2 @Signature(type=StatementHandler.class,
  3 method="parameterize",
  4 args=java.sql.Statement.class
  5 )
  6 })

  业务逻辑intercept方法中

 1 /**
 2 * 1：业务逻辑处理的方法：
 3 */
 4 @Override
 5 public Object intercept(Invocation invocation) throws Throwable {
 6 //在这里可以进行业务逻辑修改
 7 System.out.println("FirstIntercepter:===>intercept"+invocation.getMethod());
 8
 9 MetaObject metaObject = SystemMetaObject.forObject(invocation.getTarget());
10 //拿到target的元数据 StatementHandler==>ParameterHandler===>
11 //DefaultParameterHandler==>>parameterObject
12 Object value = metaObject.getValue("parameterHandler.parameterObject");
13 System.out.println("sql "+value.toString());
14 //修改完sql语句要用的参数
15 metaObject.setValue("parameterHandler.parameterObject", 2);
16 Object object = invocation.proceed();
17 return object;
18 }

• 打印log，
• 可以看到原来入参为1，现在经过拦截器修改入参为2

1 DEBUG 09-05 12:36:23,387 ==> Preparing: select * from employee where id=? (BaseJdbcLogger.java:159)
2 MySecondIntercepter====>intercept:public abstract void org.apache.ibatis.executor.statement.StatementHandler.parameterize(java.sql.Statement) throws java.sql.SQLException
3 FirstIntercepter:===>interceptpublic abstract void org.apache.ibatis.executor.statement.StatementHandler.parameterize(java.sql.Statement) throws java.sql.SQLException
4 sql 1
5 DEBUG 09-05 12:36:23,418 ==> Parameters: 2(Integer) (BaseJdbcLogger.java:159)
6 DEBUG 09-05 12:36:23,432 <== Total: 1 (BaseJdbcLogger.java:159)
7 Employee [id=2, lastName=cat, gender=0, email[email protected], depid=null]

原文地址：https://www.cnblogs.com/dgwblog/p/9591499.html