自己做网站的准备工作成人再就业培训班

开启事务过程中，如果远程调用查询当前已经开启但没有提交的事务，就会查不到数据。

示例代码

import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;import java.util.Objects;@Slf4j
@RestController
@RequestMapping("simple")
@RequiredArgsConstructor
public class SimpleController {private final SimpleObjectMapper simpleObjectMapper;private final RestTemplate restTemplate;/*** 开启事务过程中，如果远程调用查询当前已经开启但没有提交的事务，就会查不到数据。*/@GetMapping("insert")@Transactional(rollbackFor = Exception.class)//1.开启事务public void insert() {SimpleObject simpleObject = new SimpleObject();simpleObject.setId(2);simpleObject.setName("name" + System.currentTimeMillis());simpleObjectMapper.insert(simpleObject);//2.因为开启了事务，所以这里的 insert 并没有 commit，导致下面远程调用查询数据是空的。SimpleObject simpleObject1 = restTemplate.getForEntity("http://localhost:8080/simple/2", SimpleObject.class, simpleObject.getId()).getBody();log.info("simpleObject1 （这里会输出null）：{}",simpleObject1);//3.这里会输出null，因为事务没有提交，数据库不会新增数据if (Objects.isNull(simpleObject1)) {throw new RuntimeException("simpleObject1 is null");}}/*** 被远程调用的查询方法*/@GetMapping("{id}")public SimpleObject selectById(@PathVariable Integer id) {return simpleObjectMapper.selectById(id);}}

抛出异常

2024-05-23 22:49:44.033  INFO 8668 --- [nio-8080-exec-1] MyBatisSqlParsingPlugin     : Execute SQL:
INSERT INTO simple_object  ( id,name )  VALUES  ( 2,'name1716475783993' )
2024-05-23 22:49:44.119  INFO 8668 --- [nio-8080-exec-2] MyBatisSqlParsingPlugin     : Execute SQL:
SELECT id,name FROM simple_object WHERE id=2 
2024-05-23 22:49:44.149  INFO 8668 --- [nio-8080-exec-1] SimpleController        : simpleObject1 （这里会输出null）：null
2024-05-23 22:49:44.161 ERROR 8668 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : 
java.lang.RuntimeException: simpleObject1 is null

解决办法

1、去掉@Transactional注解（显然不可能，除非不影响正常的业务）
2、手动控制事务，但是有些情况下可能不适用，不适用的情况可以使用分布式事务，如：seata等（推荐）

手动控制事务

示例代码

import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.TransactionDefinition;
import org.springframework.transaction.TransactionStatus;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;import java.util.Objects;@Slf4j
@RestController
@RequestMapping("simple")
@RequiredArgsConstructor
public class SimpleController {private final SimpleObjectMapper simpleObjectMapper;private final RestTemplate restTemplate;private final PlatformTransactionManager platformTransactionManager;//事务管理器private final TransactionDefinition transactionDefinition;// 事务的一些基础信息，如超时时间、隔离级别、传播属性等/*** 使用手动事务，远程调用可以查询到数据。*/@GetMapping("insert2")public void insert2() {//手动事务不能加@Transactional注解，否则优先使用@Transactional注解的事务TransactionStatus transaction = platformTransactionManager.getTransaction(transactionDefinition);//1、手动获取事务SimpleObject simpleObject = new SimpleObject();simpleObject.setId(2);simpleObject.setName("name" + System.currentTimeMillis());simpleObjectMapper.insert(simpleObject);platformTransactionManager.commit(transaction);//2.手动提交事务SimpleObject simpleObject1 = restTemplate.getForEntity("http://localhost:8080/simple/2", SimpleObject.class, simpleObject.getId()).getBody();log.info("simpleObject1 （这里会输出simpleObject1）：{}",simpleObject1);//3.这里会输出id = 2的 SimpleObject 对象，因为事务提交，数据库会新增数据if (Objects.isNull(simpleObject1)) {throw new RuntimeException("simpleObject1 is null");}}/*** 被远程调用的查询方法*/@GetMapping("{id}")public SimpleObject selectById(@PathVariable Integer id) {return simpleObjectMapper.selectById(id);}}

不抛出异常，可以正常获取数据

2024-05-23 23:02:00.506  INFO 10608 --- [nio-8080-exec-1] c.f.m.plugin.MyBatisSqlParsingPlugin     : Execute SQL:
INSERT INTO simple_object  ( id,
name )  VALUES  ( 2,
'name1716476520466' )
2024-05-23 23:02:00.592  INFO 10608 --- [nio-8080-exec-2] c.f.m.plugin.MyBatisSqlParsingPlugin     : Execute SQL:
SELECT id,name FROM simple_object WHERE id=2 
2024-05-23 23:02:00.641  INFO 10608 --- [nio-8080-exec-1] c.f.m.controller.SimpleController        : simpleObject1 （这里会输出simpleObject1）：SimpleObject(id=2, name=name1716476520466)

不使用事务（不推荐）

示例代码

import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.TransactionDefinition;
import org.springframework.transaction.TransactionStatus;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;import java.util.Objects;@Slf4j
@RestController
@RequestMapping("simple")
@RequiredArgsConstructor
public class SimpleController {private final SimpleObjectMapper simpleObjectMapper;private final RestTemplate restTemplate;/*** 不使用事务，远程调用可以查询到数据。（不推荐）*/@GetMapping("insert3")public void insert3() {SimpleObject simpleObject = new SimpleObject();simpleObject.setId(2);simpleObject.setName("name" + System.currentTimeMillis());simpleObjectMapper.insert(simpleObject);//1、因为没有事务，所以这里会新增数据到数据库SimpleObject simpleObject1 = restTemplate.getForEntity("http://localhost:8080/simple/2", SimpleObject.class, simpleObject.getId()).getBody();log.info("simpleObject1 （这里会输出simpleObject1）：{}",simpleObject1);//2.这里会输出id = 2的 SimpleObject 对象，因为事务提交，数据库会新增数据if (Objects.isNull(simpleObject1)) {throw new RuntimeException("simpleObject1 is null");}}/*** 被远程调用的查询方法*/@GetMapping("{id}")public SimpleObject selectById(@PathVariable Integer id) {return simpleObjectMapper.selectById(id);}}

不抛出异常，可以正常获取数据

2024-05-23 23:04:31.889  INFO 10608 --- [nio-8080-exec-6] c.f.m.plugin.MyBatisSqlParsingPlugin     : Execute SQL:
INSERT INTO simple_object  ( id,
name )  VALUES  ( 2,
'name1716476671888' )
2024-05-23 23:04:31.895  INFO 10608 --- [nio-8080-exec-7] c.f.m.plugin.MyBatisSqlParsingPlugin     : Execute SQL:
SELECT id,name FROM simple_object WHERE id=2 
2024-05-23 23:04:31.897  INFO 10608 --- [nio-8080-exec-6] c.f.m.controller.SimpleController        : simpleObject1 （这里会输出simpleObject1）：SimpleObject(id=2, name=name1716476671888)