In the actual development, we always use paging query. Different database paging SQL methods are different. We can use paging plug-ins to help us separate queries. We only need to care about the data itself, not the place

1. Plug in introduction

Configure the paging plug-in in the core configuration file SqlMapConfig.xml of mybatis, for example:

<?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>
	<plugins>
		<!-- com.github.pagehelper by PageHelper Package name of class -->
		<plugin interceptor="com.github.pagehelper.PageHelper">
			<!-- Set database type Oracle,Mysql,MariaDB,SQLite,Hsqldb,PostgreSQL Six databases-->
			<property name="dialect" value="mysql"/>
		</plugin>
	</plugins>
</configuration>

2. use

There is a method startPage in PageHelper, as shown in the figure:

We found that it basically needs two parameters:

Parameter 1: pageNum current page.

Parameter 2: pageSize number of items displayed per page

These two parameters are generally passed to us by the front-end. In the front-end, there are no more than two data needed, one is the total number of records, the other is the result oriented list. Therefore, we can define a pageResult to encapsulate these two data (Map can also be used)

package entity;

import java.io.Serializable;
import java.util.List;

/**
 * Paging result class
 * @author Administrator
 * @param <T>
 */
public class PageResult<T> implements Serializable {
	private static final long serialVersionUID = -8744309372650296153L;
	
	private Long total;
	private List<T> rows;
	
	public PageResult() {
		super();
		// TODO Auto-generated constructor stub
	}
	public PageResult(Long total, List<T> rows) {
		super();
		this.total = total;
		this.rows = rows;
	}
	public Long getTotal() {
		return total;
	}
	public void setTotal(Long total) {
		this.total = total;
	}
	public List<T> getRows() {
		return rows;
	}
	public void setRows(List<T> rows) {
		this.rows = rows;
	}
	@Override
	public String toString() {
		return "PageResult [total=" + total + ", rows=" + rows + "]";
	}
	
}

PageHelper is easy to use. You only need to execute PageHelper.startPage before the SQL call statement, for example:

PageHelper.startPage(pageNum, pagesize);

At this time, when executing SQL query statements, the result of the query returns a page object, of course, it can also be a list < T > object, but we will force it to be a page object, because the page object encapsulates many methods for us to use. As shown in the picture:

We only need two methods for paging, for example;

public PageResult<TbBrand> findPage(int pageNum, int pagesize) {
		PageHelper.startPage(pageNum, pagesize);
		Page<TbBrand> page = (Page<TbBrand>) brandMapper.selectByExample(null);
		return new PageResult<>(page.getTotal(), page.getResult());
	}