MyBatis: 查询分页之拦截器

1.利用Interceptor:

package interceptor;


import java.sql.Connection;
import java.util.Map;
import java.util.Properties;
import org.apache.ibatis.executor.parameter.ParameterHandler;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.MappedStatement;
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="prepare",args={Connection.class,Integer.class})})
public class MyPageInterceptor implements Interceptor {
  
  private int page;
  private int size;
  @SuppressWarnings("unused")
  private String dbType;
 
  @SuppressWarnings("unchecked")
  @Override
  public Object intercept(Invocation invocation) throws Throwable {
    System.out.println("page plugin invoked...");
    StatementHandler statementHandler = (StatementHandler)invocation.getTarget();
    MetaObject metaObject = SystemMetaObject.forObject(statementHandler);
    while(metaObject.hasGetter("h")){
      Object object = metaObject.getValue("h");
      metaObject = SystemMetaObject.forObject(object);
    }
    while(metaObject.hasGetter("target")){
      Object object = metaObject.getValue("target");
      metaObject = SystemMetaObject.forObject(object);
    }
    MappedStatement mappedStatement = (MappedStatement)metaObject.getValue("delegate.mappedStatement");
    String mapId = mappedStatement.getId();
    if(mapId.matches(".+ByPager$")){
      ParameterHandler parameterHandler = (ParameterHandler)metaObject.getValue("delegate.parameterHandler");
      Map<String, Object> params = (Map<String, Object>)parameterHandler.getParameterObject();
      page = (int)params.get("page");
      size = (int)params.get("size");
      String sql = (String) metaObject.getValue("delegate.boundSql.sql");
      sql += " limit "+(page-1)*size +","+size;
      metaObject.setValue("delegate.boundSql.sql", sql);
    }
    return invocation.proceed();
  }
 
  @Override
  public Object plugin(Object target) {
    return Plugin.wrap(target, this);
  }
 
  @Override
  public void setProperties(Properties properties) {
    String limit = "10";
    this.page = Integer.parseInt(limit);
    this.dbType = properties.getProperty("dbType", "mysql");
  }
 
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">
  <!--  XML 配置文件包含对 MyBatis 系统的核心设置 -->
<configuration>
 
  <properties resource="db.properties"/>
  <!-- 指定 MyBatis 所用日志的具体实现 -->
  <settings>
    <setting name="logImpl" value="LOG4J"/>
  </settings>
  
  <plugins>
        <plugin interceptor="interceptor.MyPageInterceptor">
           <property name="limit" value="10"/>
            <property name="dbType" value="mysql"/> 
        </plugin>
    </plugins>
  
  <environments default="mysql">
  <!-- 环境配置，即连接的数据库。 -->
    <environment id="mysql">
   
    <!--  指定事务管理类型，type="JDBC"指直接简单使用了JDBC的提交和回滚设置 -->
      <transactionManager type="JDBC"/>
      <!--  dataSource指数据源配置，POOLED是JDBC连接对象的数据源连接池的实现。 -->
      <dataSource type="POOLED">
        <property name="driver" value="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
  <!-- mappers告诉了MyBatis去哪里找持久化类的映射文件 -->
  <mappers>
    <mapper class="org.fkit.mapper.PersonMapper"/> 
    <mapper class="org.fkit.mapper.CardMapper"/> 
    <mapper class="org.fkit.mapper.UserMapper"/>
  </mappers>
</configuration>