这篇文章主要介绍了如何使用java实现百万级别数据导出excel的相关知识，内容详细易懂，操作简单快捷，具有一定借鉴价值，相信大家阅读完这篇如何使用java实现百万级别数据导出excel文章都会有所收获，下面我们一起来看看吧。
在业务系统中，导出报表的需求会很常见，而随着时间推移业务量不断增加，数据库的数据可能达到百万甚至千万级别。对于导出报表功能，最简单的做法就是从数据库里面把需要的数据一次性加载到内存，然后写入excel文件，再把excel文件返回给用户。这种做法在数据量不大的时候是可行的，但是一旦需要导出几十万甚至上百万的数据，很可能出现OOM导致服务崩溃的情况，而且导出所消耗的时间会大大增加。
这里提供一种支持百万级别数据导出的方法，并且消耗很少的内存，核心思想就是不要一次性把数据加载到内存中。
主要是从两个方面去解决：
1.从数据库加载数据不要一次性加载，可以分页的方式或者用游标的方式分批加载数据，加载一批数据处理一批并且释放内存，这样内存占用始终处于一个比较平稳的状态。分页的方式加载编码比较繁琐，我一般是采用游标方式逐行加载。目前常用的持久层框架有JPA，mybaits,hibernate，下面会分别列出JPA，hibernate及mybatis通过游标方式加载数据。
2.写入excel也是分批写入，推荐阿里的EasyExcel，占用内存极低。
EasyExcel的pom依赖：
<dependency> <groupId>com.alibaba</groupId> <artifactId>easyexcel</artifactId> <version>2.1.1</version> <optional>true</optional> </dependency>
jdk1.8，idea2019，堆内存：-Xms256M -Xms256M(导出100万数据毫无压力)，springboot,数据库是mysql
先来张效果图，这个是最大堆内存设置为256M，两张表联合查询的情况下导出100万数据的效果，可以看到堆内存变化比较平稳，导出100万数据耗时143秒，这个速度还有优化的空间，如果是单表导出的话速度会更快些：
pom.xml:
<!-- spring web依赖，搭建web项目需要这个依赖--> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <!-- jpa --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <optional>true</optional> </dependency>
repository:
@Repository
public interface UserRepository extends JpaRepository<UserEntity,Integer> {
//@QueryHint(name = HINT_FETCH_SIZE,value = Integer.MIN_VALUE+"") 值设置为Integer.MIN_VALUE告诉mysql需要逐条返回数据，并且返回值需要用stream来接收
@QueryHints(@QueryHint(name = HINT_FETCH_SIZE,value = Integer.MIN_VALUE+""))
@Query(value = "select * from user limit 500000",nativeQuery = true)
Stream<UserEntity> findAllList();
}service:
注意:
需要加事务注解，并且是只读事务
需要及时调用entityManager的detach方法释放内存，不然还是会出现OOM
@Autowired
private EntityManager entityManager;
@Autowired
private UserRepository userRepository;
Transactional(readOnly = true)
public void exportData3(ScrollResultsHandler<UserExportVO> scrollResultsHandler){
Stream<UserEntity> allList = userRepository.findAllList.forEach((o)->{
UserEntity userEntity = (UserEntity) o;
UserExportVO userExportVO = UserExportVO.builer()
.userName(userEntity.getUsername())
.mobile(userEntity.getMobile())
.build();
scrollResultsHandler.handle(userExportVO);
//对象被session持有，调用detach方法释放内存
entityManager.detach(userEntity);
});
}controller:
@RequestMapping("export4")
public void export4(HttpServletResponse response) throws IOException {
response.setContentType("application/vnd.ms-excel");
response.setCharacterEncoding("utf-8");
String filenames="bigdata4";
response.addHeader("Content-Disposition", "filename=" + filenames + ".xlsx");
ExcelWriter excelWriter = EasyExcel.write(response.getOutputStream(), UserExportVO.class).build();
WriteSheet[] writeSheet = new WriteSheet[] {
EasyExcel.writerSheet(0, "sheet").build()
};
userService.exportData(s->{
UserExportVO resultObject = s;
ArrayList arrayList = new ArrayList<UserExportVO>();
arrayList.add(resultObject);
excelWriter.write(arrayList, writeSheet[0]);
});
excelWriter.finish();
}使用到的相关的类：
/**
* @author 奔腾的野马
* @date 2022/04/25 09:12
*/
public interface ScrollResultsHandler<T> {
void handle(T t);
}import com.alibaba.excel.annotation.ExcelProperty;
import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;
import java.math.BigDecimal;
import java.time.LocalDateTime;
/**
* @Author: 奔腾的野马
* @Date: 2021/10/16 16:19
*/
@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class UserExportVO {
@ExcelProperty(value = "用户名")
private String userName;
@ExcelProperty(value = "手机号")
private String mobile;
}pom.xml:
<dependencies> <!-- spring web依赖，搭建web项目需要这个依赖--> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> </dependency> <!--QueryDSL支持--> <dependency> <groupId>com.querydsl</groupId> <artifactId>querydsl-apt</artifactId> <version>5.0.0</version> <scope>provided</scope> </dependency> <!--QueryDSL支持--> <dependency> <groupId>com.querydsl</groupId> <artifactId>querydsl-jpa</artifactId> <version>5.0.0</version> </dependency> <dependency> <groupId>com.querydsl</groupId> <artifactId>querydsl-core</artifactId> <version>5.0.0</version> </dependency> </dependencies> <build> <plugins> <!-- QueryDSL 插件 --> <plugin> <groupId>com.mysema.maven</groupId> <artifactId>apt-maven-plugin</artifactId> <version>1.1.3</version> <executions> <execution> <goals> <goal>process</goal> </goals> <configuration> <outputDirectory>target/generated-sources/java</outputDirectory> <processor>com.querydsl.apt.jpa.JPAAnnotationProcessor</processor> </configuration> </execution> </executions> </plugin> </plugins> </build>
service:
@Autowired
private JPAQueryFactory jpaQueryFactory;
private QUserEntity qUserEntity = QUserEntity.userEntity;
@Transactional(readOnly = true)
public void exportData2(ScrollResultsHandler<UserExportVO> scrollResultsHandler){
//需要用stream方式接收，这样才能逐条处理
Stream<UserExportVO> userExportVOStream = jpaQueryFactory.select(Projections.bean(UserExportVO.class
, qUserEntity.userName, qUserEntity.mobile))
.from(qUserEntity)
//.join(xxxEntity)
//.on(xxxx)
//setHint(HINT_FETCH_SIZE,Integer.MIN_VALUE+"") 告诉mysql需要逐条返回数据,注意值需要设置为Integer.MIN_VALUE才能生效
.setHint(HINT_FETCH_SIZE,Integer.MIN_VALUE+"")
.limit(1000000)
.stream();
userExportVOStream.forEach(dto->{
scrollResultsHandler.handle(dto);
});
}controller:
@RequestMapping("export4")
public void export4(HttpServletResponse response) throws IOException {
response.setContentType("application/vnd.ms-excel");
response.setCharacterEncoding("utf-8");
String filenames="bigdata4";
response.addHeader("Content-Disposition", "filename=" + filenames + ".xlsx");
ExcelWriter excelWriter = EasyExcel.write(response.getOutputStream(), UserExportVO.class).build();
WriteSheet[] writeSheet = new WriteSheet[] {
EasyExcel.writerSheet(0, "sheet").build()
};
userService.exportData(s->{
UserExportVO resultObject = s;
ArrayList arrayList = new ArrayList<UserExportVO>();
arrayList.add(resultObject);
excelWriter.write(arrayList, writeSheet[0]);
});
excelWriter.finish();
}pom.xml:
<dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.9</version> </dependency>
dao:
/**
* @author 奔腾的野马
* @date 2022/04/16 19:14
*/
@Mapper
public interface UserDao {
//ResultSetType.TYPE_FORWORD_ONLY 结果集的游标只能向下滚动,fetchSize需要设置为Integer.MIN_VALUE游标才能生效
@Options(resultSetType = ResultSetType.FORWARD_ONLY,fetchSize = Integer.MIN_VALUE)
@ResultType(UserExportVO.class)
@Select("select userName,mobile from user limit 500000")
void reportAll2(ResultHandler<UserExportVO> handler);
}service:
@Transactional(readOnly = true)
public void export2(ResultHandler<UserExportVO> handler){
userDao.reportAll2(handler);
}controller:
同上
service:
@Autowired
private EntityManager entityManager;
public void exportData(ScrollResultsHandler<UserExportVO> scrollResultsHandler){
//当不需要缓存时，最好使用StatelessSession
StatelessSession session = ((Session) entityManager.getDelegate()).getSessionFactory().openStatelessSession();
Query query = session.getNamedQuery("getAllList");
query.setCacheMode(CacheMode.IGNORE);
//setFetchSize(Integer.MIN_VALUE)告诉mysql逐条返回数据
query.setFetchSize(Integer.MIN_VALUE);
query.setFirstResult(0);
query.setMaxResults(1000000);
query.setReadOnly(true);
query.setLockMode("a", LockMode.NONE);
//ScrollMode.TYPE_FORWORD_ONLY 结果集的游标只能向下滚动
ScrollableResults results = query.scroll(ScrollMode.FORWARD_ONLY);
while (results.next()) {
UserEntity userEntity = (UserEntity) results.get(0);
UserExportVO userExportVO = UserExportVO.builer()
.userName(userEntity.getUsername())
.mobile(userEntity.getMobile())
.build();
scrollResultsHandler.handle(userExportVO);
}
results.close();
session.close();
}controller：
同上
1.1 项目中使用了log4jdbc-log4j2-jdbc4.1(版本是1.16),驱动为net.sf.log4jdbc.sql.jdbcapi.DriverSpy，改成mysql的原生驱动就好了。"log4jdbc-log4j2-jdbc4.1"本来是用来开发过程中方便打印sql的，结果却带来了OOM问题，看来使用第三方jar包一定要慎重啊。
1.2 项目的存在多个版本的querydsl，jar包冲突，解决jar包就正常了
1.3 二次查询时，hibernate的一级缓存没有及时释放，进一步分析，发现大量的对象都被缓存在（org.hibernate.engine.StatefulPersistenceContext）中，导致一级缓存泄漏
解决方法：
由于 Hibernate 的一级缓存是其内部使用的，无法关闭或停用（随着Session 销毁）。从Hibernate 的手册或文档中可知，Hibernate 的一级缓存的清除可通过以下方式：
1）对于单个对象的清除：
Session session=sessionFactory.getCurrentSession(); session.evict(entity);
2）对于实体集合的清除：
Session session=sessionFactory.getCurrentSession(); session.clear();建议在程序中加入对 Hibernate 一级缓存的清除工作，以便可以其内存数据可以及时释放。
导出过程中遍历stream需要二次查询数据库时提示"Streaming result set com.mysql.cj.protocol.a.result.ResultsetRowsStreaming@5800daf5 is still active. No statements may be issued when any streaming result sets are open and in use on a given connection. Ensure that you have called .close() on any active streaming result sets before attempting more queries"
错误详细内容:
java.sql.SQLException: Streaming result set com.mysql.cj.protocol.a.result.ResultsetRowsStreaming@3b8732ec is still active. No statements may be issued when any streaming result sets are open and in use on a given connection. Ensure that you have called .close() on any active streaming result sets before attempting more queries. at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129) at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97) at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122) at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:953) at com.mysql.cj.jdbc.ClientPreparedStatement.executeQuery(ClientPreparedStatement.java:1003) at net.sf.log4jdbc.sql.jdbcapi.PreparedStatementSpy.executeQuery(PreparedStatementSpy.java:780) at com.zaxxer.hikari.pool.ProxyPreparedStatement.executeQuery(ProxyPreparedStatement.java:52) at com.zaxxer.hikari.pool.HikariProxyPreparedStatement.executeQuery(HikariProxyPreparedStatement.java) at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:57) at org.hibernate.loader.Loader.getResultSet(Loader.java:2292) at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:2050) at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:2012) at org.hibernate.loader.Loader.doQuery(Loader.java:953) at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:354) at org.hibernate.loader.Loader.doList(Loader.java:2838) at org.hibernate.loader.Loader.doList(Loader.java:2820) at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2652) at org.hibernate.loader.Loader.list(Loader.java:2647) at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:506) at org.hibernate.hql.internal.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:396) at org.hibernate.engine.query.spi.HQLQueryPlan.performList(HQLQueryPlan.java:219) at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1404) at org.hibernate.query.internal.AbstractProducedQuery.doList(AbstractProducedQuery.java:1562) at org.hibernate.query.internal.AbstractProducedQuery.list(AbstractProducedQuery.java:1530) at org.hibernate.query.internal.AbstractProducedQuery.getSingleResult(AbstractProducedQuery.java:1578) at org.hibernate.query.criteria.internal.compile.CriteriaQueryTypeQueryAdapter.getSingleResult(CriteriaQueryTypeQueryAdapter.java:111) at org.springframework.data.jpa.repository.query.JpaQueryExecution$SingleEntityExecution.doExecute(JpaQueryExecution.java:196) at org.springframework.data.jpa.repository.query.JpaQueryExecution.execute(JpaQueryExecution.java:88) at org.springframework.data.jpa.repository.query.AbstractJpaQuery.doExecute(AbstractJpaQuery.java:154) at org.springframework.data.jpa.repository.query.AbstractJpaQuery.execute(AbstractJpaQuery.java:142) at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:618) at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:605) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:80) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:366) at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:99) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:139) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:149) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:95) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) at com.sun.proxy.$Proxy223.countAllByDeliveryNo(Unknown Source)
查阅资料后发现，是mysql不支持在流式查询过程中使用同一连接再次查询数据库
解决方法：
方法1.使用异步方法查询，这样就可以规避同一个连接二次查询的问题
方法2.需要二次查询时开启一个新的事务去查询就可以，spring中可以使用事务注解开启新的事务就搞定了，注解如下：
@Transactional(propagation = Propagation.REQUIRES_NEW,readOnly = true)
关于“如何使用java实现百万级别数据导出excel”这篇文章的内容就介绍到这里，感谢各位的阅读！相信大家对“如何使用java实现百万级别数据导出excel”知识都有一定的了解，大家如果还想学习更多知识，欢迎关注亿速云行业资讯频道。
免责声明：本站发布的内容（图片、视频和文字）以原创、转载和分享为主，文章观点不代表本网站立场，如果涉及侵权请联系站长邮箱：is@yisu.com进行举报，并提供相关证据，一经查实，将立刻删除涉嫌侵权内容。
