mybatis介绍
MyBatis 是一款优秀的持久层框架，它支持定制化 SQL、存储过程以及高级映射。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以使用简单的 XML 或注解来配置和映射原生类型、接口和 Java 的 POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。
mybatis架构图
mybatis框架结构.png
我们这个demo实现就是基于mybatis的插件模块（主要实现mybatis的Interceptor接口）
Interceptor接口
package org.apache.ibatis.plugin;
import java.util.Properties;
/**
* @author Clinton Begin
*/
public interface Interceptor {
Object intercept(Invocation invocation) throws Throwable;
Object plugin(Object target);
void setProperties(Properties properties);
}
demo实现
主要技术 spring boot + mybatis
pom.xml
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>1.3.2</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
数据库 DDL
create table user
(
id int auto_increment primary key,
username varchar(20) null
);
核心代码
PageVo
需要的分页要继承这个类
public class PageVo {
protected int page = 1;//当前页数，默认为1
protected int rows = 15;//每页显示条数,默认为15
private int offset = 0;//每页起始条数
private int limit = 15;//每页结束条数
public int getLimit() {
return (page - 1) * rows;
}
public void setLimit(int limit) {
this.limit = limit;
}
public int getOffset() {
return page * rows;
}
public void setOffset(int offset) {
this.offset = (page - 1) * rows;
}
public int getPage() {
return page;
}
public void setPage(int page) {
this.page = page;
}
public int getRows() {
return rows;
}
public void setRows(int rows) {
this.rows = rows;
}
}
返回结果集
用于封装返回的结果集
package com.wtn.mybatis_plugs.util;
import java.util.List;
public class PageResult<T> {
private int pageNo = 1;// 页码，默认是第一页
private int pageSize = 3;// 每页显示的记录数，默认是15
private int total;// 总记录数
private int totalPage;// 总页数
private List<T> rows;
private int offset = 0;// 偏移量，当前页起始记录数
private int limit = 15;
private boolean count = true;
public PageResult() {
}
public PageResult(int pageNo, int pageSize, int total, List<T> rows) {
this.pageNo = pageNo;
this.pageSize = pageSize;
this.total = total;
this.setRows(rows);
int totalPage = total % pageSize == 0 ? total / pageSize : total / pageSize + 1;
this.setTotalPage(totalPage);
}
public List<T> getRows() {
return rows;
}
public void setRows(List<T> rows) {
this.rows = rows;
}
public int getOffset() {
return offset;
}
public void setOffset(int offset) {
// this.offset = offset;
this.offset = (this.pageNo - 1) * pageSize;
}
public int getLimit() {
return limit;
}
public void setLimit(int limit) {
this.limit = limit;
}
public boolean isCount() {
return count;
}
public void setCount(boolean count) {
this.count = count;
}
@Override
public String toString() {
return "Page [pageNo=" + pageNo + ", pageSize=" + pageSize + ", totalRecord=" + total + ", totalPage="
+ totalPage + ", rows=" + rows + ", offset=" + offset + ", limit=" + limit + ", count=" + count + "]";
}
public int getPageNo() {
return pageNo;
}
public void setPageNo(int pageNo) {
this.pageNo = pageNo;
}
public int getPageSize() {
return pageSize;
}
public void setPageSize(int pageSize) {
this.pageSize = pageSize;
}
public int getTotal() {
return total;
}
public void setTotal(int total) {
this.total = total;
int totalPage = total % pageSize == 0 ? total / pageSize : total / pageSize + 1;
this.setTotalPage(totalPage);
}
public int getTotalPage() {
return totalPage;
}
public void setTotalPage(int totalPage) {
this.totalPage = totalPage;
}
}
拦截器部分
主要思路是判断是否继承我们的PageVo这个类，如果继承了就进行分页处理，我这里分页重新拼接sql执行
@Override
public Object intercept(Invocation invocation) throws Throwable {
logger.info("进入拦截器");
Object[] args = invocation.getArgs();
MappedStatement mappedStatement = (MappedStatement) args[0];
//获取参数
Object param = invocation.getArgs()[1];
BoundSql boundSql = mappedStatement.getBoundSql(param);
Object parameterObject = boundSql.getParameterObject();
/**
* 判断是否是继承PageVo来判断是否需要进行分页
*/
if (parameterObject instanceof PageVo) {
//强转 为了拿到分页数据
PageVo pagevo = (PageVo) param;
String sql = boundSql.getSql();
//获取相关配置
Configuration config = mappedStatement.getConfiguration();
Connection connection = config.getEnvironment().getDataSource().getConnection();
//拼接查询当前条件的sql的总条数
String countSql = "select count(*) from (" + sql + ") a";
PreparedStatement preparedStatement = connection.prepareStatement(countSql);
BoundSql countBoundSql = new BoundSql(config, countSql, boundSql.getParameterMappings(), boundSql.getParameterObject());
ParameterHandler parameterHandler = new DefaultParameterHandler(mappedStatement, parameterObject, countBoundSql);
parameterHandler.setParameters(preparedStatement);
//执行获得总条数
ResultSet rs = preparedStatement.executeQuery();
int count = 0;
if (rs.next()) {
count = rs.getInt(1);
}
//拼接分页sql
String pageSql = sql + " limit " + pagevo.getLimit() + " , " + pagevo.getOffset();
//重新执行新的sql
doNewSql(invocation, pageSql);
Object result = invocation.proceed();
connection.close();
//处理新的结构
PageResult<?> pageResult = new PageResult<List>(pagevo.page, pagevo.rows, count, (List) result);
List<PageResult> returnResultList = new ArrayList<>();
returnResultList.add(pageResult);
return returnResultList;
}
return invocation.proceed();
}
测试结构
@PostMapping("/findUserPage")
public List<User> findUserPage(@RequestBody UserDto userDto){
return userService.findUserPage(userDto);
}
测试结果
Snip20190403_2.png
