利用mybatis generator插件生成基于分页语句及分页解决方案

1》

虽然MyBatis_Generator可以将常用的DAO中的方法都生成,但是唯独忽视了一点——分页,虽然MyBatis支持分页,但是那个分页是内存分页,如果数据量大的话内存恐怕要承受不了,于是就自动动手改造自动化工具生成的代码使其支持真分页.

本文里面我说的是针对mysql的,针对其他数据库的请做适当修改,因为mybatis底层没有封装数据库的差异,所以我觉得也并没有必要对其差异进行封装.

其实改动的东西很简单,也很少,切入点就是Mapper里面的动态sql:

首先在Example对象里面加入两个整形变量start和limit,start代表起始索引,limit代表数量,然后生成对应的get/set方法,使MyBatis在执行的时候能够获取相应的值.

第二部就是修改Mapper了,在selectByExample里面加入对Example对象中start和limit的判断,如果start和limit不同时为0,则自动在sql的最后加入分页条件,以下是需要加入的xml代码,记得加在selectByExample这个sql的最后面,也就是排序的后面

<if test="start !=0 or limit!=0">
limit #{start},#{limit}
</if>

2》
Mybatis分页-利用Mybatis Generator插件生成基于数据库方言的分页语句，统计记录总数

众所周知，Mybatis本身没有提供基于数据库方言的分页功能，而是基于JDBC的游标分页，很容易出现性能问题。网上有很多分页的解决方案，不外乎是基于Mybatis本机的插件机制，通过拦截Sql做分页。但是在像Oracle这样的数据库上，拦截器生成的Sql语句没有变量绑定，而且每次语句的都要去拦截，感觉有点浪费性能。

Mybatis Generator是Mybatis的代码生成工具，可以生成大部分的查询语句。

本文提供的分页解决方案是新增Mybatis Generator插件，在用Mybatis Generator生成Mybatis代码时，直接生成基于数据库方言的Sql语句，解决Oralce等数据库的变量绑定，且无需使用Mybatis拦截器去拦截语句判断分页。

一、编写Mybatis Generator Dialect插件

/**

* Copyright (C) 2011 Tgwoo Inc.
* http://www.tgwoo.com/ */
package com.tgwoo.core.dao.plugin;

import java.util.List;

import org.mybatis.generator.api.CommentGenerator;
import org.mybatis.generator.api.IntrospectedTable;
import org.mybatis.generator.api.PluginAdapter;
import org.mybatis.generator.api.dom.java.Field;
import org.mybatis.generator.api.dom.java.FullyQualifiedJavaType;
import org.mybatis.generator.api.dom.java.JavaVisibility;
import org.mybatis.generator.api.dom.java.Method;
import org.mybatis.generator.api.dom.java.Parameter;
import org.mybatis.generator.api.dom.java.TopLevelClass;
import org.mybatis.generator.api.dom.xml.Attribute;
import org.mybatis.generator.api.dom.xml.Document;
import org.mybatis.generator.api.dom.xml.TextElement;
import org.mybatis.generator.api.dom.xml.XmlElement;

/**
* @author pan.wei
* @date 2011-11-30 下午08:36:11
*/
public class OraclePaginationPlugin extends PluginAdapter {

@Override
public boolean modelExampleClassGenerated(TopLevelClass topLevelClass,
IntrospectedTable introspectedTable) {
// add field, getter, setter for limit clause
addPage(topLevelClass, introspectedTable, "page");
return super.modelExampleClassGenerated(topLevelClass,
introspectedTable);
}

@Override
public boolean sqlMapDocumentGenerated(Document document,
IntrospectedTable introspectedTable) {
XmlElement parentElement = document.getRootElement();

// 产生分页语句前半部分
XmlElement paginationPrefixElement = new XmlElement("sql");
paginationPrefixElement.addAttribute(new Attribute("id",
"OracleDialectPrefix"));
XmlElement pageStart = new XmlElement("if");
pageStart.addAttribute(new Attribute("test", "page != null"));
pageStart.addElement(new TextElement(
"select * from ( select row_.*, rownum rownum_ from ( "));
paginationPrefixElement.addElement(pageStart);
parentElement.addElement(paginationPrefixElement);

// 产生分页语句后半部分
XmlElement paginationSuffixElement = new XmlElement("sql");
paginationSuffixElement.addAttribute(new Attribute("id",
"OracleDialectSuffix"));
XmlElement pageEnd = new XmlElement("if");
pageEnd.addAttribute(new Attribute("test", "page != null"));
pageEnd.addElement(new TextElement(
"<![CDATA[ ) row_ ) where rownum_ > #{page.begin} and rownum_ <= #{page.end} ]]>"));
paginationSuffixElement.addElement(pageEnd);
parentElement.addElement(paginationSuffixElement);

return super.sqlMapDocumentGenerated(document, introspectedTable);
}

@Override
public boolean sqlMapSelectByExampleWithoutBLOBsElementGenerated(
XmlElement element, IntrospectedTable introspectedTable) {

XmlElement pageStart = new XmlElement("include"); //$NON-NLS-1$
pageStart.addAttribute(new Attribute("refid", "OracleDialectPrefix"));
element.getElements().add(0, pageStart);

XmlElement isNotNullElement = new XmlElement("include"); //$NON-NLS-1$
isNotNullElement.addAttribute(new Attribute("refid",
"OracleDialectSuffix"));
element.getElements().add(isNotNullElement);

return super.sqlMapUpdateByExampleWithoutBLOBsElementGenerated(element,
introspectedTable);
}

/**
* @param topLevelClass
* @param introspectedTable
* @param name
*/
private void addPage(TopLevelClass topLevelClass,
IntrospectedTable introspectedTable, String name) {
topLevelClass.addImportedType(new FullyQualifiedJavaType(
"com.tgwoo.core.dao.pojo.Page"));
CommentGenerator commentGenerator = context.getCommentGenerator();
Field field = new Field();
field.setVisibility(JavaVisibility.PROTECTED);
field.setType(new FullyQualifiedJavaType("com.tgwoo.core.dao.pojo.Page"));
field.setName(name);
commentGenerator.addFieldComment(field, introspectedTable);
topLevelClass.addField(field);
char c = name.charAt(0);
String camel = Character.toUpperCase(c) + name.substring(1);
Method method = new Method();
method.setVisibility(JavaVisibility.PUBLIC);
method.setName("set" + camel);
method.addParameter(new Parameter(new FullyQualifiedJavaType(
"com.tgwoo.core.dao.pojo.Page"), name));
method.addBodyLine("this." + name + "=" + name + ";");
commentGenerator.addGeneralMethodComment(method, introspectedTable);
topLevelClass.addMethod(method);
method = new Method();
method.setVisibility(JavaVisibility.PUBLIC);
method.setReturnType(new FullyQualifiedJavaType(
"com.tgwoo.core.dao.pojo.Page"));
method.setName("get" + camel);
method.addBodyLine("return " + name + ";");
commentGenerator.addGeneralMethodComment(method, introspectedTable);
topLevelClass.addMethod(method);
}

/**
* This plugin is always valid - no properties are required
*/
public boolean validate(List<String> warnings) {
return true;
}
}

二、增加插件到Mybatis Generator配置文件中

<?xml version="1.0" encoding="UTF-8" ?>

<!DOCTYPE generatorConfiguration PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN" "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd" >
<generatorConfiguration >
<classPathEntry location="E:\work\eclipseWorkspace\myEclipse\CTSPMTS\WebRoot\WEB-INF\lib\ojdbc14.jar" />

<context id="oracle" >
<plugin type="org.mybatis.generator.plugins.CaseInsensitiveLikePlugin"></plugin>
<plugin type="org.mybatis.generator.plugins.SerializablePlugin"></plugin>
<!-- Pagination -->
<plugin type="com.tgwoo.core.dao.plugin.OraclePaginationPlugin"></plugin>

<commentGenerator>
<property name="suppressDate" value="true" />
<property name="suppressAllComments" value="true" />
</commentGenerator>

<jdbcConnection driverClass="oracle.jdbc.driver.OracleDriver" connectionURL="jdbc:oracle:thin:@192.168.0.2:1521:ctspmt" userId="ctspmt" password="ctspmt123" />
<javaModelGenerator targetPackage="com.tgwoo.ctspmt.model" targetProject="CTSPMTS/src" />
<sqlMapGenerator targetPackage="com.tgwoo.ctspmt.data" targetProject="CTSPMTS/src" />
<javaClientGenerator targetPackage="com.tgwoo.ctspmt.data" targetProject="CTSPMTS/src" type="XMLMAPPER" /><!--

<table schema="ctspmt" tableName="mt_e_interface_log"/>
--><!--
<table schema="ctspmt" tableName="mt_e_msg" />
<table schema="ctspmt" tableName="mt_e_msg_log" />
<table schema="ctspmt" tableName="mt_e_msg_receiver" />
<table schema="ctspmt" tableName="st_e_org" />
<table schema="ctspmt" tableName="st_e_role" />
<table schema="ctspmt" tableName="st_e_user" />
<table schema="ctspmt" tableName="mt_e_user_msg_conf" />
<table schema="ctspmt" tableName="mt_j_user_device" />
<table schema="ctspmt" tableName="st_j_user_role" />
<table schema="ctspmt" tableName="ST_E_UNIQUE_KEY" />
--><table schema="ctspmt" tableName="mt_v_msg_item" />
</context>

</generatorConfiguration>

三、示例

/**

* Copyright (C) 2011 Tgwoo Inc.
* http://www.tgwoo.com/ */
package com.tgwoo.ctspmt.test;

import com.tgwoo.core.config.SpringBeanProxy;
import com.tgwoo.core.dao.pojo.Page;
import com.tgwoo.ctspmt.data.MtVMsgItemMapper;
import com.tgwoo.ctspmt.model.MtVMsgItemExample;

/**
* @author pan.wei
* @date 2011-11-25 下午01:26:17
*/
public class Test {
/**
* @param args
*/
public static void main(String[] args) {
//get spring mapper instance
MtVMsgItemMapper mapper = SpringBeanProxy.getCtx().getBean(
MtVMsgItemMapper.class);
MtVMsgItemExample ex = new MtVMsgItemExample();
Page page = new Page(0, 10);
ex.setPage(page);
ex.createCriteria().andMsgCodeEqualTo("222");
// set count,up to you
page.setCount(mapper.countByExample(ex));
int row = mapper.selectByExample(ex).size();
System.out.println("============row:" + row + "================");
}

}

四、分页类

package com.tgwoo.core.dao.pojo;

/**
* @author pan.wei
* @date 2011-12-1 上午11:36:12
*/
public class Page {
// 分页查询开始记录位置
private int begin;
// 分页查看下结束位置
private int end;
// 每页显示记录数
private int length;
// 查询结果总记录数
private int count;
// 当前页码
private int current;
// 总共页数
private int total;

public Page() {
}

/**
* 构造函数
*
* @param begin
* @param length
*/
public Page(int begin, int length) {
this.begin = begin;
this.length = length;
this.end = this.begin + this.length;
this.current = (int) Math.floor((this.begin * 1.0d) / this.length) + 1;
}

/**
* @param begin
* @param length
* @param count
*/
public Page(int begin, int length, int count) {
this(begin, length);
this.count = count;
}

/**
* @return the begin
*/
public int getBegin() {
return begin;
}

/**
* @return the end
*/
public int getEnd() {
return end;
}

/**
* @param end
*            the end to set
*/
public void setEnd(int end) {
this.end = end;
}

/**
* @param begin
*            the begin to set
*/
public void setBegin(int begin) {
this.begin = begin;
if (this.length != 0) {
this.current = (int) Math.floor((this.begin * 1.0d) / this.length) + 1;
}
}

/**
* @return the length
*/
public int getLength() {
return length;
}

/**
* @param length
*            the length to set
*/
public void setLength(int length) {
this.length = length;
if (this.begin != 0) {
this.current = (int) Math.floor((this.begin * 1.0d) / this.length) + 1;
}
}

/**
* @return the count
*/
public int getCount() {
return count;
}

/**
* @param count
*            the count to set
*/
public void setCount(int count) {
this.count = count;
this.total = (int) Math.floor((this.count * 1.0d) / this.length);
if (this.count % this.length != 0) {
this.total++;
}
}

/**
* @return the current
*/
public int getCurrent() {
return current;
}

/**
* @param current
*            the current to set
*/
public void setCurrent(int current) {
this.current = current;
}

/**
* @return the total
*/
public int getTotal() {
if (total == 0) {
return 1;
}
return total;
}

/**
* @param total
*            the total to set
*/
public void setTotal(int total) {
this.total = total;
}

}

五、生成后的代码

1、Example代码

package com.tgwoo.ctspmt.model;

import com.tgwoo.core.dao.pojo.Page;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Date;
import java.util.Iterator;
import java.util.List;

public class MtVMsgItemExample {
protected String orderByClause;

protected boolean distinct;

protected List<Criteria> oredCriteria;

protected Page page;

...

2、mapper.xml

...
<select id="selectByExample" resultMap="BaseResultMap" parameterType="com.tgwoo.ctspmt.model.MtVMsgItemExample" >
<include refid="OracleDialectPrefix" />
select
<if test="distinct" >
distinct
</if>
<include refid="Base_Column_List" />
from CTSPMT.MT_V_MSG_ITEM
<if test="_parameter != null" >
<include refid="Example_Where_Clause" />
</if>
<if test="orderByClause != null" >
order by ${orderByClause}
</if>
<include refid="OracleDialectSuffix" />
</select>
...
<sql id="OracleDialectPrefix" >
<if test="page != null" >
select * from ( select row_.*, rownum rownum_ from (
</if>
</sql>
<sql id="OracleDialectSuffix" >
<if test="page != null" >
<![CDATA[ ) row_ ) where rownum_ > #{page.begin} and rownum_ <= #{page.end} ]]>
</if>
</sql>
...

附件是Mybatis Generatorjar包。

其他数据库的方言可以按照Oracle的去改写，有写好的希望能共享下。

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

maven管理：

1、pom.xml

<build>
<plugins>
<plugin>
<groupId>org.mybatis.generator</groupId>
<artifactId>mybatis-generator-maven-plugin</artifactId>
<version>1.3.1</version>
<executions>
<execution>
<id>Generate MyBatis Artifacts</id>
<goals>
<goal>generate</goal>
</goals>
</execution>
</executions>
<dependencies>
<dependency>
<groupId>com.oracle</groupId>
<artifactId>ojdbc14</artifactId>
<version>10.2.0.4.0</version>
</dependency>
</dependencies>
</plugin>
</plugins>
</build>

2、generatorConfig.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration
PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
"http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>
<context id="oracleGenerator" targetRuntime="MyBatis3">
<plugin type="org.mybatis.generator.plugins.CaseInsensitiveLikePlugin"></plugin>
<plugin type="org.mybatis.generator.plugins.SerializablePlugin"></plugin>
<!-- Pagination -->
<plugin
type="com.tgwoo.test.core.dao.mybatis.generator.plugin.pagination.OraclePaginationPlugin"></plugin>

<!-- 取消注释 -->
<commentGenerator>
<property name="suppressDate" value="true" />
<property name="suppressAllComments" value="true" />
</commentGenerator>
<!-- 配置连接数据信息 -->
<jdbcConnection driverClass="oracle.jdbc.driver.OracleDriver"
connectionURL="jdbc:oracle:thin:@192.168.0.2:1521:test" userId="test"
password="test123" />
<javaTypeResolver>
<property name="forceBigDecimals" value="false" />
</javaTypeResolver>

<!-- 配置自动生成的Model的保存路径与其它参数 -->
<javaModelGenerator targetPackage="com.tgwoo.test.dao.model"
targetProject=".\src\main\java">
<property name="enableSubPackages" value="false" />
<property name="trimStrings" value="true" />
</javaModelGenerator>

<!-- 配置自动生成的Mappper.xml映射的保存路径与其它参数 -->
<sqlMapGenerator targetPackage="com.tgwoo.test.dao"
targetProject=".\src\main\resources">
<property name="enableSubPackages" value="false" />
</sqlMapGenerator>

<!-- 配置自动生成的Mappper.java接口的保存路径与其它参数 -->
<javaClientGenerator type="XMLMAPPER"
targetPackage="com.tgwoo.test.dao" targetProject=".\src\main\java">
<property name="enableSubPackages" value="false" />
</javaClientGenerator>

<!-- 生成表对应的操作与实体对象 -->
<table schema="test" tableName="testTable">
<columnOverride column="id" javaType="Long" />
</table>
</context>
</generatorConfiguration>

3、run

Goals:mybatis-generator:generate

4、注意事项

报插件无法找到或者无法实例化的一般是分页插件和maven插件不在同一classloader下引起的，需要在mybatis-generator-maven-plugin的dependencies中增加dependency。

1 楼 hellostory 2012-02-07
如果是做【高级查询】分页显示，你这个如何实现？

2 楼 daquan198163 2012-02-08
Good，太有用了！

3 楼 chengfengmuyu 2012-02-19



4 楼 hgdakfg 2012-03-21

hellostory 写道
如果是做【高级查询】分页显示，你这个如何实现？

写视图.

5 楼 panqili2120 2012-05-28
很强大 支持 呵呵，但在我们用的Page一般的begin是从1开始的， 也就是说上面的SQL的这部分也改成row_ ) where rownum_ >= #{page.begin}这样

6 楼 duohuoteng 2012-07-06