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

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！