Java如何使用MyBatis框架分页

2024-11-24 技术教程 151

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初始准备

1.创建分页对象类，方便模块间传值

//PageInfo.javaimport lombok.Data;@Datapublic class PageInfo { private int pageNo; private int pageSize;}

2.定义DAO层接口

import org.apache.ibatis.session.RowBounds;import org.springframework.stereotype.Repository;import java.util.List;@Repositorypublic interface UserMapper { User selectByUser(User user); List<User> selectAll(); List<User> selectByPageInfo(PageInfo info); List<User> selectByInterceptor(PageInfo info); List<User> selectByRowBounds(RowBounds rowBounds);}

3.mapper中定义结果集合BaseResult

一、原始切分：最原始方法，不建议使用

1.mapper代码:查询所有数据

<select id="selectAll" resultMap="BaseResult"> select * from tb_user</select>

2.业务层代码:利用List的subList()方法对数据进行切片

public List<User> findByAll(PageInfo info) { List<User> users = userMapper.selectAll(); return users.subList(info.getPageNo(), info.getPageSize()); }

3.控制层代码

@RequestMapping(value = "/userlist_1", method = RequestMethod.GET)@ResponseBody public Result findUserBySubList(PageInfo info) { List<User> users = userService.findByAll(info); if(users.size() == 0) { return ResultGenerator.genFailResult("未查找到用户"); } return ResultGenerator.genSuccessResult(users); }

二、LIMIT关键字

1.mapper代码:利用limit关键字实现分页

<select id="selectByPageInfo" resultMap="BaseResult"> select * from tb_user limit #{pageNo}, #{pageSize}</select>

2.业务层直接调用

public List<User> findByPageInfo(PageInfo info) { return userMapper.selectByPageInfo(info); }

3.控制层直接调用

三、RowBounds实现分页

1.在DAO层定义好所要传输的分页信息，类型为RowBounds

2.mapper层：查询所有数据

3.业务层：将PageInfo信息封装成RowBounds,调用DAO层方法

public List<User> findByRowBounds(PageInfo info) { return userMapper.selectByRowBounds(new RowBounds(info.getPageNo(), info.getPageSize())); }

4.控制层直接调用

四、MyBatis的Interceptor实现:实现复杂，需要明白MyBatis的实现

1.创建Interceptor

import org.apache.ibatis.executor.parameter.ParameterHandler;import org.apache.ibatis.executor.statement.StatementHandler;import org.apache.ibatis.mapping.MappedStatement;import org.apache.ibatis.plugin.*;import org.apache.ibatis.reflection.MetaObject;import org.apache.ibatis.reflection.SystemMetaObject;import java.sql.Connection;import java.util.Properties;/** * 利用MyBatis拦截器进行分页 * * @Intercepts 说明是一个拦截器 * @Signature 拦截器的签名 * type 拦截的类型四大对象之一( Executor,ResultSetHandler,ParameterHandler,StatementHandler) * method 拦截的方法 * args 参数,高版本需要加个Integer.class参数,不然会报错 * */@Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})})public class DefinedPageInterceptor implements Interceptor { @Override public Object intercept(Invocation invocation) throws Throwable { //获取StatementHandler,默认的是RoutingStatementHandler StatementHandler statementHandler = (StatementHandler) invocation.getTarget(); //获取StatementHandler的包装类 MetaObject metaObject = SystemMetaObject.forObject(statementHandler); //分隔代理对象 while (metaObject.hasGetter("h")) { Object obj = metaObject.getValue("h"); metaObject = SystemMetaObject.forObject(obj); } while (metaObject.hasGetter("target")) { Object obj = metaObject.getValue("target"); metaObject = SystemMetaObject.forObject(obj); } //获取查看接口映射的相关信息 MappedStatement mappedStatement = (MappedStatement) metaObject.getValue("delegate.mappedStatement"); String mapId = mappedStatement.getId(); //拦截以ByInterceptor结尾的请求，统一实现分页 if (mapId.matches(".+ByInterceptor$")) { System.out.println("LOG:已触发分页拦截器"); //获取进行数据库操作时管理参数的Handler ParameterHandler parameterHandler = (ParameterHandler) metaObject.getValue("delegate.parameterHandler"); //获取请求时的参数 PageInfo info = (PageInfo) parameterHandler.getParameterObject(); //获取原始SQL语句 String originalSql = (String) metaObject.getValue("delegate.boundSql.sql"); //构建分页功能的SQL语句 String sql = originalSql.trim() + " limit " + info.getPageNo() + ", " + info.getPageSize(); metaObject.setValue("delegate.boundSql.sql", sql); } //调用原对象方法，进入责任链下一级 return invocation.proceed(); } @Override public Object plugin(Object target) { //生成Object对象的动态代理对象 return Plugin.wrap(target, this); } @Override public void setProperties(Properties properties) { //如果分页每页数量是统一的，可以在这里进行统一配置，也就无需再传入PageInfo信息了 }}

2.将Interceptor添加至MyBatisConfig中，这里采用JavaConfig的方式

@Bean public SqlSessionFactoryBean sqlSession() { SqlSessionFactoryBean sqlSession = new SqlSessionFactoryBean(); sqlSession.setDataSource(dataSource()); try { Resource[] resources = new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"); sqlSession.setMapperLocations(resources); //配置自定义的Interceptro作为MyBatis的Interceptor,完成分页操作 DefinedPageInterceptor definedPageInterceptor = new DefinedPageInterceptor(); sqlSession.setPlugins(new Interceptor[]{definedPageInterceptor}); return sqlSession; } catch (IOException e) { e.printStackTrace(); } return null; }

3.DAO层接口方法名需要和代码中自定义的".+ByInterceptor$"正则表达式相匹配,mapper的书写依然是查询所有数据

<select id="selectByInterceptor" resultMap="BaseResult"> select * from tb_user</select>

4.业务层直接调用

5.控制层直接调用

五、开源项目PageHelper实现：本质还是自己封装了个Interceptor

1.引入PageHelper的jar包

<dependency> <groupId>com.github.pagehelper</groupId> <artifactId>pagehelper</artifactId> <version>5.1.10</version></dependency>

2.配置PageInterceptor

public PageInterceptor initPageInterceptor(){ PageInterceptor pageInterceptor = new PageInterceptor(); Properties properties = new Properties(); //设置数据库类型 properties.setProperty("helperDialect", "mysql"); //该参数默认为false //设置为true时，会将RowBounds第一个参数offset当成pageNum页码使用 //和startPage中的pageNum效果一样 properties.setProperty("offsetAsPageNum", "true"); //该参数默认为false //设置为true时，使用RowBounds分页会进行count查询 properties.setProperty("rowBoundsWithCount", "true"); pageInterceptor.setProperties(properties); return pageInterceptor; } @Bean public SqlSessionFactoryBean sqlSession() { SqlSessionFactoryBean sqlSession = new SqlSessionFactoryBean(); sqlSession.setDataSource(dataSource()); try { Resource[] resources = new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"); sqlSession.setMapperLocations(resources); //配置PageHelper作为MyBatis的Interceptor，完成分页操作 PageInterceptor pageInterceptor = this.initPageInterceptor(); //配置自定义的Interceptro作为MyBatis的Interceptor,完成分页操作 DefinedPageInterceptor definedPageInterceptor = new DefinedPageInterceptor(); sqlSession.setPlugins(new Interceptor[]{pageInterceptor, definedPageInterceptor}); return sqlSession; } catch (IOException e) { e.printStackTrace(); } return null; }

3.mapper依然是查询所有数据

4.为DAO层再封装一次方法

@Repositorypublic class PageHelperHandler { @Autowired private SqlSessionFactory sqlSessionFactory; public List<User> findByPageHelper(PageInfo info) { SqlSession session = sqlSessionFactory.openSession(); PageHelper.startPage(info.getPageNo(), info.getPageSize()); //写到要使用到的类名和方法名 List<User> users = session.selectList("cn.edu.yau.mapper.UserMapper.selectAll"); return users; }}

6.业务层直接调用Handler

7.控制层直接调用

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