MyBatis Generator实现MySQL分页插件，新增插件PaginationPlugin方法

项目链接：https://github.com/daydayRen/Mybaties-Generator

MyBatis Generator本身是有分页功能，废话不多说，让我们先看看他是怎么实现的：

我使用的Generator

配置文件generatorConfig.xm：

旧 RowBoundsPlugin：

generatorConfig.xml配置自带的分页功能

运行主函数生成

int offset = 100;
int limit = 25;
RowBounds rowBounds = new RowBounds(offset, limit);
List list = TMapper.selectByExampleWithRowbounds(example, rowBounds);

 RowBounds的构造方法new RowBounds(offset, limit)中的offset、limit参数就相当于MySQL的select语句limit后的offset和rows。如果此时仔细观察一下日志打出来的SQL语句或者看下生成的XxxMapper.xml文件中的selectByExampleWithRowbounds元素，可以发现select语句并没有使用limit。实际上RowBounds原理是通过ResultSet的游标来实现分页，也就是并不是用select语句的limit分页而是用Java代码分页，查询语句的结果集会包含符合查询条件的所有数据，使用不慎会导致性能问题，所以并不推荐使用RowBoundsPlugin来实现分页

新 PaginationPlugin:

实现过程：

首先创建我们的实现代码

package org.mybatis.generator.plugins.page;
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.JavaVisibility;
import org.mybatis.generator.api.dom.java.Method;
import org.mybatis.generator.api.dom.java.Parameter;
import org.mybatis.generator.api.dom.java.PrimitiveTypeWrapper;
import org.mybatis.generator.api.dom.java.TopLevelClass;
import org.mybatis.generator.api.dom.xml.Attribute;
import org.mybatis.generator.api.dom.xml.TextElement;
import org.mybatis.generator.api.dom.xml.XmlElement;
 
/**
 * 
File name : PaginationPlugin.java 
 * 
Author : fly 
 
 * 
Date : 2013-7-2 上午11:50:45 
 * 
Extent:2018 yitianRen
 *    添加注释，方便理解和实现更多功能
 */
public class PaginationPlugin extends PluginAdapter {
    @Override
    public boolean modelExampleClassGenerated(TopLevelClass topLevelClass,
            IntrospectedTable introspectedTable) {
        // add field, getter, setter for limit clause
    	addPageNo(topLevelClass, introspectedTable, "pageNo");//当前页
        addStartRow(topLevelClass, introspectedTable, "startRow");//开始行
        addPageSize(topLevelClass, introspectedTable, "pageSize");//每页行数
        return super.modelExampleClassGenerated(topLevelClass,
                introspectedTable);
    }
    /**
     * 添加查询分页功能
     */
    @Override
    public boolean sqlMapSelectByExampleWithoutBLOBsElementGenerated(
            XmlElement element, IntrospectedTable introspectedTable) {
//        XmlElement isParameterPresenteElemen = (XmlElement) element
//                .getElements().get(element.getElements().size() - 1);
        XmlElement isNotNullElement = new XmlElement("if"); //$NON-NLS-1$  if标签
        //test="startRow != null" sql语句
        isNotNullElement.addAttribute(new Attribute("test", "startRow != null")); //$NON-NLS-1$ //$NON-NLS-2$  
//        isNotNullElement.addAttribute(new Attribute("compareValue", "0")); //$NON-NLS-1$ //$NON-NLS-2$
        isNotNullElement.addElement(new TextElement("limit #{startRow} , #{pageSize}"));
//        isParameterPresenteElemen.addElement(isNotNullElement);
        element.addElement(isNotNullElement);
        return super.sqlMapUpdateByExampleWithoutBLOBsElementGenerated(element, introspectedTable);
    }
    private void addStartRow(TopLevelClass topLevelClass,
            IntrospectedTable introspectedTable, String name) {
        CommentGenerator commentGenerator = context.getCommentGenerator();
        Field field = new Field();
        field.setVisibility(JavaVisibility.PROTECTED);
//        field.setType(FullyQualifiedJavaType.getIntInstance());
        field.setType(PrimitiveTypeWrapper.getIntegerInstance());
        field.setName(name);
//        field.setInitializationString("-1");
        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(PrimitiveTypeWrapper.getIntegerInstance(), name));
        method.addBodyLine("this." + name + "=" + name + ";");
        commentGenerator.addGeneralMethodComment(method, introspectedTable);
        topLevelClass.addMethod(method);
        method = new Method();
        method.setVisibility(JavaVisibility.PUBLIC);
        method.setReturnType(PrimitiveTypeWrapper.getIntegerInstance());
        method.setName("get" + camel);
        method.addBodyLine("return " + name + ";");
        commentGenerator.addGeneralMethodComment(method, introspectedTable);
        topLevelClass.addMethod(method);
    }
    private void addPageSize(TopLevelClass topLevelClass,
    		IntrospectedTable introspectedTable, String name) {
    	CommentGenerator commentGenerator = context.getCommentGenerator();
    	Field field = new Field();
    	field.setVisibility(JavaVisibility.PROTECTED);
//        field.setType(FullyQualifiedJavaType.getIntInstance());
    	field.setType(PrimitiveTypeWrapper.getIntegerInstance());
    	field.setName(name);
        field.setInitializationString("10");
    	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(PrimitiveTypeWrapper.getIntegerInstance(), name));
    	method.addBodyLine("this." + name + "=" + name + ";");
    	//this.startRow = (pageNo-1)*this.pageSize;
        method.addBodyLine("this.startRow = (pageNo-1)*this." + name + ";");
    	commentGenerator.addGeneralMethodComment(method, introspectedTable);
    	topLevelClass.addMethod(method);
    	method = new Method();
    	method.setVisibility(JavaVisibility.PUBLIC);
    	method.setReturnType(PrimitiveTypeWrapper.getIntegerInstance());
    	method.setName("get" + camel);
    	method.addBodyLine("return " + name + ";");
    	commentGenerator.addGeneralMethodComment(method, introspectedTable);
    	topLevelClass.addMethod(method);
    }
    private void addPageNo(TopLevelClass topLevelClass,
    		IntrospectedTable introspectedTable, String name) {
    	CommentGenerator commentGenerator = context.getCommentGenerator();
    	Field field = new Field();
    	field.setVisibility(JavaVisibility.PROTECTED);
//        field.setType(FullyQualifiedJavaType.getIntInstance());
    	field.setType(PrimitiveTypeWrapper.getIntegerInstance());
    	field.setName(name);
        field.setInitializationString("1");
    	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(PrimitiveTypeWrapper.getIntegerInstance(), name));
    	method.addBodyLine("this." + name + "=" + name + ";");
    	method.addBodyLine("this.startRow = (" + name + "-1)*this.pageSize;");
    	commentGenerator.addGeneralMethodComment(method, introspectedTable);
    	topLevelClass.addMethod(method);
    	method = new Method();
    	method.setVisibility(JavaVisibility.PUBLIC);
    	method.setReturnType(PrimitiveTypeWrapper.getIntegerInstance());
    	method.setName("get" + camel);
    	method.addBodyLine("return " + name + ";");
    	commentGenerator.addGeneralMethodComment(method, introspectedTable);
    	topLevelClass.addMethod(method);
    }
    /**
     * This plugin is always valid - no properties are required
     * 这个插件总是有效的——不需要属性
     */
    public boolean validate(List warnings) {
        return true;
    }
 
}

 

配置：

运行主函数：

你会看到我们的Example类中多了三个字段，就是我们最开始分页使用的一些参数

public class AinfoExample {
    protected String orderByClause;

    protected boolean distinct;

    protected List oredCriteria;

    protected String fields;

    protected Integer pageNo = 1;//当前页

    protected Integer startRow;//开始位置

    protected Integer pageSize = 10;//每页大小
......

Mapper.xml中：

使用limit分页完成

还有另一种实现方式感觉也不错，可能习惯了 以前的分页的方式还没有尝试，链接：https://blog.csdn.net/wo240/article/details/52576711