mybatisplus PageHelper
https://blog.csdn.net/yangjiechao945/article/details/80707804
PageHelper用于查询语句分页，让分页更简单、代码更优雅。如果硬是要纠结效率与资源，那您倒是直接手写BaseDao哇....
集成mybatis-plus，代码中添加分页相关配置
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/**
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* mybatis-plus分页插件
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* 文档：http://mp.baomidou.com
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*/
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@Bean
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public PaginationInterceptor paginationInterceptor() {
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PaginationInterceptor page =
new PaginationInterceptor();
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page.setDialectType(
"mysql");
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// 打开PageHelper localPage 模式
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page.setLocalPage(
true);
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return page;
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}
这样就能使用PageHelper来分页了，当然要问了，为什么必须要手动设置打开呢？那就直接看源码咯~
直贴关键代码，具体源码请查阅：PaginationInterceptor.java
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package com.baomidou.mybatisplus.plugins;
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/**
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*
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* 分页拦截器
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*
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*
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* @author hubin
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* @Date 2016-01-23
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*/
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@Intercepts({
@Signature(type = StatementHandler.class, method =
"prepare", args = {Connection.class, Integer.class})})
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public
class PaginationInterceptor implements Interceptor {
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/* 是否开启 PageHelper localPage 模式 */
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private
boolean localPage =
false;
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/**
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* Physical Pagination Interceptor for all the queries with parameter {@link org.apache.ibatis.session.RowBounds}
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*/
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public Object intercept(Invocation invocation) throws Throwable {
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StatementHandler statementHandler = (StatementHandler) PluginUtils.realTarget(invocation.getTarget());
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MetaObject metaStatementHandler = SystemMetaObject.forObject(statementHandler);
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// 先判断是不是SELECT操作
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MappedStatement mappedStatement = (MappedStatement) metaStatementHandler.getValue(
"delegate.mappedStatement");
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if (!SqlCommandType.SELECT.equals(mappedStatement.getSqlCommandType())) {
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return invocation.proceed();
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}
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RowBounds rowBounds = (RowBounds) metaStatementHandler.getValue(
"delegate.rowBounds");
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/* 不需要分页的场合 */
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if (rowBounds ==
null || rowBounds == RowBounds.DEFAULT) {
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// 本地线程分页
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if (
localPage) {
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// 采用ThreadLocal变量处理的分页
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rowBounds = PageHelper.getPagination();
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if (rowBounds ==
null) {
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return invocation.proceed();
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}
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}
else {
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// 无需分页
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return invocation.proceed();
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}
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}
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// 针对定义了rowBounds，做为mapper接口方法的参数
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BoundSql boundSql = (BoundSql) metaStatementHandler.getValue(
"delegate.boundSql");
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String originalSql = boundSql.getSql();
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Connection connection = (Connection) invocation.getArgs()[
0];
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DBType dbType = StringUtils.isNotEmpty(dialectType) ? DBType.getDBType(dialectType) : JdbcUtils.getDbType(connection.getMetaData().getURL());
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if (rowBounds
instanceof Pagination) {
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Pagination page = (Pagination) rowBounds;
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boolean orderBy =
true;
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if (page.isSearchCount()) {
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SqlInfo sqlInfo = SqlUtils.getCountOptimize(sqlParser, originalSql);
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orderBy = sqlInfo.isOrderBy();
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this.queryTotal(overflowCurrent, sqlInfo.getSql(), mappedStatement, boundSql, page, connection);
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if (page.getTotal() <=
0) {
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return invocation.proceed();
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}
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}
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String buildSql = SqlUtils.concatOrderBy(originalSql, page, orderBy);
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originalSql = DialectFactory.buildPaginationSql(page, buildSql, dbType, dialectClazz);
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}
else {
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// support physical Pagination for RowBounds
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originalSql = DialectFactory.buildPaginationSql(rowBounds, originalSql, dbType, dialectClazz);
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}
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/*
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*
禁用内存分页
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*
内存分页会查询所有结果出来处理（这个很吓人的），如果结果变化频繁这个数据还会不准。
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*/
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metaStatementHandler.setValue(
"delegate.boundSql.sql", originalSql);
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metaStatementHandler.setValue(
"delegate.rowBounds.offset", RowBounds.NO_ROW_OFFSET);
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metaStatementHandler.setValue(
"delegate.rowBounds.limit", RowBounds.NO_ROW_LIMIT);
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return invocation.proceed();
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}
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public void setLocalPage(boolean localPage) {
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this.localPage = localPage;
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}
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}
关键地方已标红，在PaginationInterceptor中，是否开启 PageHelper localPage 模式，默认是关闭的，需要手动打开
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/* 是否开启 PageHelper localPage 模式 */
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private
boolean localPage =
false;
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public
class PageHelper {
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// 分页本地线程变量
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private
static
final ThreadLocal
LOCAL_PAGE =
new ThreadLocal<>();
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/**
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*
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* 获取分页
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*
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*
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* @return
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*/
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public static Pagination getPagination() {
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return LOCAL_PAGE.get();
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}
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/**
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*
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* 设置分页
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*
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*
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* @param page
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*/
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public static void setPagination(Pagination page) {
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LOCAL_PAGE.set(page);
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}
好，接下来使用就方便了
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// 组装查询条件
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EntityWrapper
wrapper =
new EntityWrapper<>();
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if (
null != status) {
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wrapper.eq(
"status", status);
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}
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// 设置分页参数
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PageHelper.startPage(pageIndex, pageSize);
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// 执行查询
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List
platfProjects = UserMapper.selectList(wrapper);
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// 返回的分页参数
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Pagination pagination = PageHelper.getPagination();
就是这样~