MyBatis拦截器实现mysql与oracle共用分页

最近笔者在做公司项目从oracle到mysql的迁移，大家都知道mysql分页采用的是limit，而oracle采用的是rownum，为了不在oracle和mysql对应的mapper文件,分别写对应的分页，这里可以使用mybatis自带的拦截器插件实现。
下面分一下几个步骤进行介绍：
一、准备工作；
二、myBatis.xml拦截器配置；
三、拦截器interceptor实现；
四、效果展示。

一、准备工作

首先，准备model，User.java:

package com.qiyongkang.model;

public class User extends BaseEntity {

    private static final long serialVersionUID = 1L;

    private int Id;

    private String UserName;

    private int Age;

    public User() {}

    public int getId() {
        return Id;
    }

    public void setId(int id) {
        Id = id;
    }

    public String getUserName() {
        return UserName;
    }

    public void setUserName(String userName) {
        UserName = userName;
    }

    public int getAge() {
        return Age;
    }

    public void setAge(int age) {
        Age = age;
    }

    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return this.getId() + "==" + this.getUserName() + "==" + this.getAge();
    }

}

然后就是User类的父类，BaseEntity.java,此类是用于分页、排序用：

package com.qiyongkang.model;

import java.io.Serializable;

public class BaseEntity implements Serializable{
    private static final long serialVersionUID = 1L;

    private String sort;

    private String order;

    private int currentPage = 0;

    public int getCurrentPage() {
        return currentPage;
    }

    public void setCurrentPage(int currentPage) {
        this.currentPage = currentPage;
    }

    public int getPageSize() {
        return pageSize;
    }

    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }

    private int pageSize = 5;

    public String getSort() {
        return sort;
    }

    public void setSort(String sort) {
        this.sort = sort;
    }

    public String getOrder() {
        return order;
    }

    public void setOrder(String order) {
        this.order = order;
    }

    @Override
    public String toString() {
        return "BaseEntity [sort=" + sort + ", order=" + order + ", currentPage=" + currentPage + ", pageSize="
                + pageSize + "]";
    }

}

然后，再就是User实体对于的mapper.xml和mapper接口：
UserMapper.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.qiyongkang.mybatis.UserMapper">
  <resultMap type="User" id="userMap">
    <id property="Id" column="Id"/>
    <result property="UserName" column="UserName"/>
    <result property="Age" column="Age"/>
  </resultMap>
  <select id="getUserList" resultMap="userMap" parameterType="User">
    SELECT * FROM user 
    <where>
      <if test="UserName != null and UserName != ''">userName LIKE '%%'</if>
    </where>
    <if test="sort != null and order != null and sort != '' and order != ''">
        ORDER BY ${sort} ${order}
    </if>
  </select>
</mapper>    

UserMapper.java接口：

package com.qiyongkang.mybatis;

import java.util.HashMap;
import java.util.List;

import com.qiyongkang.model.BaseEntity;
import com.qiyongkang.model.User;

public interface UserMapper {
    public List<User> getUserList(BaseEntity baseEntity);
}

再就是连接数据库的属性文件配置jdbc.properties:

#######MySql#########
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://127.0.0.1:3306/test
username=root
password=123456
db=mysql

########Oracle#######
#driver=oracle.jdbc.driver.OracleDriver
#url=jdbc:oracle:thin:@127.0.0.1:1521:ORCL
#username=username
#password=password 

二、myBatis.xml拦截器配置

接下来，再来看看拦截器的配置：

<?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">
<configuration>
  <properties resource="jdbc.properties"></properties>

  <typeAliases>
    <package name="com.qiyongkang.model"/>
  </typeAliases>

  <plugins>
    <plugin interceptor="com.qiyongkang.interceptor.PageSqlHandleInterceptor"></plugin>
  </plugins>

  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
      <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>
    <mapper resource="com/qiyongkang/model/UserMapper.xml"/>
  </mappers>

</configuration>    

这里在plugins标签中配置的就是拦截器，它必须实现Interceptor接口。注意，这里笔者没有与spring集成。

三、拦截器interceptor实现

接下来，再来看看拦截器中，其实这个拦截器的功能就是在sql执行前，对sql语句进行统一的包装改变，然后再执行。

package com.qiyongkang.interceptor;

import java.lang.reflect.Field;
import java.util.Properties;

import org.apache.ibatis.executor.statement.RoutingStatementHandler;
import org.apache.ibatis.mapping.BoundSql;
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 com.qiyongkang.model.BaseEntity;

@Intercepts({ @org.apache.ibatis.plugin.Signature(type = org.apache.ibatis.executor.statement.StatementHandler.class, method = "prepare", args = { java.sql.Connection.class }) })
public class PageSqlHandleInterceptor implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        RoutingStatementHandler statement = (RoutingStatementHandler) invocation.getTarget();
        BoundSql boundSql = statement.getBoundSql();
        String sql = boundSql.getSql();

        System.out.println("分页前：" + sql);

        BaseEntity baseEntity = (BaseEntity) boundSql.getParameterObject();
        System.out.println("当前页：" + baseEntity.getCurrentPage() + "==页大小：" + baseEntity.getPageSize());


        //获取currentPage, pageSize
        int currentPage = baseEntity.getCurrentPage();
        int pageSize = baseEntity.getPageSize();

        //从jdbc.properties
        Properties prop = new Properties();
        prop.load(PageSqlHandleInterceptor.class.getClassLoader().getResourceAsStream("jdbc.properties"));
        String db = prop.getProperty("db");

        if ("mysql".equals(db)) {
            sql = getLimitStringMysql(sql, (currentPage - 1) * pageSize, pageSize);
        } else if ("oracle".equals(db)) {
            sql = getLimitStringOracle(sql, (currentPage - 1) * pageSize, currentPage * pageSize);
        }

        setClassField(boundSql, "sql", sql);
        System.out.println("分页前：" + sql);
        return invocation.proceed();
    }

    @Override
    public Object plugin(Object obj) {
        return Plugin.wrap(obj, this);
    }

    @Override
    public void setProperties(Properties properties) {

    }

    /** * Oracle分页 * @param sql * @param offset * @param limit * @return */
    public String getLimitStringOracle(String sql, int offset, int limit) {
        sql = sql.trim();
        boolean isForUpdate = false;
        if (sql.toLowerCase().endsWith(" for update")) {
            sql = sql.substring(0, sql.length() - 11);
            isForUpdate = true;
        }
        StringBuffer pagingSelect = new StringBuffer(sql.length() + 100);
        if (offset > 0) {
            pagingSelect.append("select * from ( select row_.*, rownum rownum_ from ( ");
        } else {
            pagingSelect.append("select * from ( ");
        }
        pagingSelect.append(sql);
        if (offset > 0) {
            pagingSelect.append(" ) row_ ) where rownum_ <= " + limit + " and rownum_ > " + offset);
        } else {
            pagingSelect.append(" ) where rownum <= " + limit);
        }
        if (isForUpdate) {
            pagingSelect.append(" for update");
        }
        return pagingSelect.toString();
    }

    /** * mysql分页 * @param sql * @param offset * @param limit * @return */
    public String getLimitStringMysql(String sql, int offset, int limit) {
        sql = sql.trim();
        boolean isForUpdate = false;
        if (sql.toLowerCase().endsWith(" for update")) {
            sql = sql.substring(0, sql.length() - 11);
            isForUpdate = true;
        }
        StringBuffer pagingSelect = new StringBuffer(sql.length() + 100);
        if (offset < 0) {
            offset = 0;
        }
        pagingSelect.append(sql);
        pagingSelect.append(" limit " + offset + "," + limit);

        if (isForUpdate) {
            pagingSelect.append(" for update");
        }
        return pagingSelect.toString();
    }

    /** * 通过反射获取某个类的属性 * * @param clazz * @param name * @return * @throws Exception */
    private static Field getField(Class<?> clazz, String name) throws Exception {
        Field field = null;
        for (Field f : clazz.getDeclaredFields()) {
            if (f.getName().equals(name)) {
                f.setAccessible(true);
                field = f;
            }
        }
        return field;
    }

    public static void setClassField(Object obj, String name, Object value) throws Exception {
        Field field = getField(obj.getClass(), name);
        field.set(obj, value);
    }

}

四、效果展示

mysql：

oracle:

项目包结构:

最后来看看，调用测试类Test.java:

package com.qiyongkang.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.qiyongkang.model.User;
import com.qiyongkang.mybatis.UserMapper;

public class Test {

    public static void main(String[] args) {
        //Get the SqlSessionFactory
        String resource = "myBatis.xml";
        SqlSession session = null;
        try {
            InputStream inputStream = Resources.getResourceAsStream(resource);

            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

            //Get a sqlSession
            session = sqlSessionFactory.openSession();

            //Get the mapper
            UserMapper userMapper = session.getMapper(UserMapper.class);

            //Get user list
            User user3 = new User();
            user3.setId(5);
            user3.setUserName("1");
            user3.setAge(14);
            user3.setCurrentPage(2);
            user3.setPageSize(5);
            user3.setSort("userName");
            user3.setOrder("desc");
            List<User> userList = userMapper.getUserList(user3);

            session.commit();

            System.out.println(userList.size());

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            session.close();
        }

    }

}

就讲到这儿啦，大家有什么疑问的或者一些好的建议，可以给我留言，谢谢！