MyBatis 如何编写一个自定义插件？

灰太狼 2022-12-18 12:53 258阅读 0赞

### 先看如何自定义一个插件 ###

1、新建类实现 Interceptor 接口，并指定想要拦截的方法签名

/**
     * MyBatis 插件
     */
    @Intercepts({@Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})})
    public class ExamplePlugin implements Interceptor {
    
        @Override
        public Object intercept(Invocation invocation) throws Throwable {
            for (Object arg : invocation.getArgs()) {
                System.out.println("参数：" + arg);
            }
            System.out.println("方法：" + invocation.getMethod());
            System.out.println("目标对象：" + invocation.getTarget());
            Object result = invocation.proceed();
    
            //只获取第一个数据
            if (result instanceof List){
                System.out.println("原集合数据：" + result);
                System.out.println("只获取第一个对象");
                List list = (List)result;
                return Arrays.asList(list.get(0));
            }
            return result;
        }
    }

2、MyBatis 配置文件中添加该插件

测试代码

System.out.println("------userMapper.deleteUsers()------");
    //删除 user
    userMapper.deleteUsers();
    
    System.out.println("------userMapper.insertUser()------");
    //插入 user
    for (int i = 1; i <= 5; i++) {
        userMapper.insertUser(new User(i, "ConstXiong" + i));
    }
    
    System.out.println("------userMapper.selectUsers()------");
    //查询所有 user
    List<User> users = userMapper.selectUsers();
    System.out.println(users);

打印结果

------userMapper.deleteUsers()------
    ------userMapper.insertUser()------
    ------userMapper.selectUsers()------
    参数：org.apache.ibatis.mapping.MappedStatement@58c1c010
    参数：null
    参数：org.apache.ibatis.session.RowBounds@b7f23d9
    参数：null
    方法：public abstract java.util.List org.apache.ibatis.executor.Executor.query(org.apache.ibatis.mapping.MappedStatement,java.lang.Object,org.apache.ibatis.session.RowBounds,org.apache.ibatis.session.ResultHandler) throws java.sql.SQLException
    目标对象：org.apache.ibatis.executor.CachingExecutor@61d47554
    原集合数据：[User{id=1, name='ConstXiong1', mc='null'}, User{id=2, name='ConstXiong2', mc='null'}, User{id=3, name='ConstXiong3', mc='null'}, User{id=4, name='ConstXiong4', mc='null'}, User{id=5, name='ConstXiong5', mc='null'}]
    只获取第一个对象
    [User{id=1, name='ConstXiong1', mc='null'}]

插件功能的官网说明

> MyBatis 允许你在映射语句执行过程中的某一点进行拦截调用。默认情况下，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)

完整 Demo：

[https://www.javanav.com/val/a5535343f9b545eda9665f03d62345ba.html][https_www.javanav.com_val_a5535343f9b545eda9665f03d62345ba.html]

PS：MyBatis 分页插件 PagerHelper，就是一个很好的插件学习例子。

--------------------

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