Mybatis九（ mybatis插件的原理及使用）

1.插件执行原理

　　

 一、demo

　　1.测试类

@Test
    public void test1() {
        String resource = "mybatis-config.xml";
        InputStream inputStream;
        try {
            inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();
            sqlSession.clearCache();
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            User selectUserById = mapper.selectUser(12);
            System.out.println(selectUserById);
            sqlSession.commit();
            // 释放资源
            sqlSession.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

2.plugin

　　对封装参数进行拦截

package plugin;

import java.util.Properties;

import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.plugin.Intercepts;
import org.apache.ibatis.plugin.Invocation;
import org.apache.ibatis.plugin.Plugin;
import org.apache.ibatis.plugin.Signature;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.reflection.SystemMetaObject;
@Intercepts({
    @Signature(type=StatementHandler.class ,method="parameterize",args=java.sql.Statement.class)
})
public class ParamPlugin implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        // TODO Auto-generated method stub
        System.out.println("interceptor开始：");
        Object target = invocation.getTarget();
        System.out.println("当前拦截目标对象："+target);
        //拿到：StatementHandler==>parameterHandler==>parameterObject
        //拿到target的元数据
        MetaObject metaObject = SystemMetaObject.forObject(target);
        System.out.println(metaObject);
        Object value = metaObject.getValue("parameterHandler.parameterObject");
        System.out.println("sql语句的参数是："+value);
        //修改sql语句的参数
        metaObject.setValue("parameterHandler.parameterObject", 14);
        //执行目标方法并返回
        return invocation.proceed();
    }

    @Override
    public Object plugin(Object target) {
        // TODO Auto-generated method stub
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {
        // TODO Auto-generated method stub

    }

}

3.

  <plugins>
        <plugin interceptor="plugin.ParamPlugin"></plugin>
    </plugins>

二、mybatis分页基于plugin实现原理

　　1.配置plugin

<plugin interceptor="com.github.pagehelper.PageInterceptor">
        <!-- config params as the following -->
       <!--  <property name="param1" value="value1"/> -->
    </plugin>

2.使用插件分页

String resource = "mybatis-config.xml";
            InputStream inputStream;
            try {
                inputStream = Resources.getResourceAsStream(resource);
                SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
                SqlSession sqlSession = sqlSessionFactory.openSession();
                UserMapper mapper = sqlSession.getMapper(UserMapper.class);
//                Page<Object> page = PageHelper.startPage(2,3);
//                List<User> users = mapper.selectAllUser();
//                for (User user: users) {
//                    System.out.println(user.toString());
//                }
//                System.out.println("当前页码："+page.getPageNum());
//                System.out.println("总记录数："+page.getTotal());
//                System.out.println("每页记录数："+page.getPageSize());
//                System.out.println("总页码数："+page.getPages());
                PageHelper.startPage(1, 10);
                List<User> list = mapper.selectAllUser();
                //用PageInfo对结果进行包装
                PageInfo page = new PageInfo(list,5);
                //测试PageInfo全部属性
                //PageInfo包含了非常全面的分页属性
//                assertEquals(1, page.getPageNum());
//                assertEquals(10, page.getPageSize());
//                assertEquals(1, page.getStartRow());
//                assertEquals(10, page.getEndRow());
//                assertEquals(183, page.getTotal());
//                assertEquals(19, page.getPages());
//                assertEquals(1, page.getFirstPage());
//                assertEquals(8, page.getLastPage());
//                assertEquals(true, page.isFirstPage());
//                assertEquals(false, page.isLastPage());
//                assertEquals(false, page.isHasPreviousPage());
//                assertEquals(true, page.isHasNextPage());
                sqlSession.commit();
                // 释放资源
                sqlSession.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }