前言

大家在开发中有没有遇到过因循环依赖导致项目启动失败？在排查循环依赖的过程中有没困难？如何避免写出循环依赖的代码？

我没写过循环依赖的代码，作为稳定性负责人，我排查过多次。

有些逻辑简单的代码，循环依赖很容易排查。但是，我们的业务超级复杂，绝大多数循环依赖，一整天都查不出来。

起初我们遇到一个循环依赖处理一个，作为稳定性负责人，技术能干的事，不会让人做第二次，为此，我写了一段循环依赖巡检代码，把循环依赖扼杀在测试环境。

下面介绍下场景及处理思路，未必最优，欢迎交流。

背景

SpringCloud服务在上线时出现BeanCurrentlyInCreationException异常（服务本地启动无异常，测试环境启动也无异常，上线就偶尔异常）。

1，本地模拟如下：

Caused by: org.springframework.beans.factory.BeanCurrentlyInCreationException:

Error creating bean with name 'studentA': Bean with name 'studentA'

has been injected into other beans [studentC] in its raw version as part of a circular reference, but has eventually been wrapped.

This means that said other beans do not use the final version of the bean.

This is often the result of over-eager type matching - consider using 'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.

2，生产场景如下图：

SpringCloud BeanCurrentlyInCreationException 异常解决方案-LMLPHP

异常排查&模拟

经过生产排查和本地测试，产生此异常的场景如下：

1，如果类方法有@Async注解，则可能出现如上异常

2，如果存在循环依赖，并且类方法上有@Async注解，则必然会出现如上异常。

1，场景演示：

在spring中，基于field属性的循环依赖是可以的:

SpringCloud BeanCurrentlyInCreationException 异常解决方案-LMLPHP

示例代码：

@Service
@Slf4j
public class StudentA {

    @Autowired
    private StudentB studentB;
    public String test(){
        return studentB.test();
    }
    public String test1(){
        return "Studenta1";
    }
}

@Slf4j
@Service
public class StudentB {

    @Autowired
    private StudentC studentC;

    public String test() {
        return "Studentb";
    }

    public String test1() {
        return studentC.test1();
    }
}

@Slf4j
@Service
public class StudentC {

    @Autowired
    private StudentA studentA;

    public String test() {
        return studentA.test();
    }

    public String test1() {
        return "Studentc1";
    }
}

@Autowired
private StudentA studentA ;
@Test
public void testA(){
    String v= studentA.test();
    log.info("testa={}",v);
}

以上代码输出正常

2，异常演示

如果我们的方法加上了@Async 注解。则抛出异常：

@Service
@Slf4j
public class StudentA {

    @Autowired
    private StudentB studentB;
    @Async
    public String test(){
        return studentB.test();
    }
    @Async
    public String test1(){
        return "Studenta1";
    }
}

@Slf4j
@Service
public class StudentB {

    @Autowired
    private StudentC studentC;
    @Async
    public String test() {
        return "Studentb";
    }
    @Async
    public String test1() {
        return studentC.test1();
    }
}

@Slf4j
@Service
public class StudentC {

    @Autowired
    private StudentA studentA;
    @Async
    public String test() {
        return studentA.test();
    }
    @Async
    public String test1() {
        return "Studentc1";
    }
}

@Autowired
private StudentA studentA ;
@Test
public void testA(){
    String v= studentA.test();
    log.info("testa={}",v);
}
Caused by: org.springframework.beans.factory.BeanCurrentlyInCreationException:
Error creating bean with name 'studentA': Bean with name 'studentA' has been injected into other beans [studentC] in its raw version as part of a circular reference, but has eventually been wrapped.
This means that said other beans do not use the final version of the bean.
This is often the result of over-eager type matching - consider using 'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.

3，解决异常

A,B,C三个类中，至少一个类的field 必须加@Lazy

@Service
@Slf4j
public class StudentA {

    @Autowired
    @Lazy
    private StudentB studentB;
    @Async
    public String test(){
        return studentB.test();
    }
    @Async
    public String test1(){
        return "Studenta1";
    }
}

@Slf4j
@Service
public class StudentB {

    @Autowired
    @Lazy
    private StudentC studentC;
    @Async
    public String test() {
        return "Studentb";
    }
    @Async
    public String test1() {
        return studentC.test1();
    }
}

@Slf4j
@Service
public class StudentC {

    @Autowired
    @Lazy
    private StudentA studentA;
    @Async
    public String test() {
        return studentA.test();
    }
    @Async
    public String test1() {
        return "Studentc1";
    }
}

参考：https://my.oschina.net/tridays/blog/805111

杜绝循环依赖的解决方案

这里根据我司的服务架构介绍一下如何避免循环依赖，我司用的spring cloud 全家桶，注册中心用的consul，配置中心有config 和apollo。

1，查看bean的依赖

spring-cloud 提供了bean信息查看功能,通过ip:端口+/actuator/beans可查看(如何配置actuator这里不详细讨论)，如下图，我们可以看到每个bean依赖的bean

2，解析bean及其依赖beans

如上，我们可以查看某个bean的依赖项，由此，我们可以递归查找bean是否存在循环引用。

SpringCloud BeanCurrentlyInCreationException 异常解决方案-LMLPHP

bean 信息模型

@Data
public class ApplicationBeans {

    private Map<String, ContextBeans> contexts;
}



@Data
public class ContextBeans {

    private Map<String, BeanDescriptor> beans;
    private String parentId;
}

3，代码实现

这里检测项目起名alarm-center，检测类为CheckCyclicDependenceService

@Slf4j
@RefreshScope
@Service
public class CheckCyclicDependenceService {

    // 服务发现
    @Autowired
    private DiscoveryClient discoveryClient;

    //默认检测 api,admin两个项目，如果想检测其它项目，可在config配置
    @Value("${check-serviceids-value:api,admin}")
    private String checkServiceIds;

 
    //入口
    public void checkCyclicDependence() {
        if (Strings.isNullOrEmpty(checkServiceIds)) {
            return;
        }
        List<String> serviceIds = Arrays.asList(checkServiceIds.split(","));
        for (String serviceId : serviceIds) {
            long start = System.currentTimeMillis();
            RestTemplate restTemplate = new RestTemplate();
            //根据服务名去consul找一个服务实例
            ServiceInstance instance = discoveryClient.getInstances(serviceId).get(0);
            String url = instance.getUri() + "/actuator/beans";
            //所有的beans信息
            String applicationBeansStr = restTemplate.getForObject(url, String.class);
            ApplicationBeans applicationBeans = JSONObject.parseObject(applicationBeansStr, ApplicationBeans.class);
            long end = System.currentTimeMillis();
            log.info("checkCyclicDependence get applicationBeans end,serviceid={},coust={}", serviceId, (end - start));
            Map<String, ContextBeans> contexts = applicationBeans.getContexts();
            Map<String, BeanDescriptor> qualifiedBeans = new HashMap<>();
            for (Map.Entry<String, ContextBeans> conEntry : contexts.entrySet()) {
                if (!conEntry.getKey().startsWith(serviceId)) {
                    continue;
                }
                ContextBeans contextBeans = conEntry.getValue();
                Map<String, BeanDescriptor> beans = contextBeans.getBeans();

                for (Map.Entry<String, BeanDescriptor> entry1 : beans.entrySet()) {
                    String beanName = entry1.getKey().toLowerCase();
                    BeanDescriptor beanDescriptor = entry1.getValue();
                    if (!beanDescriptor.getType().startsWith("com.shuidihuzhu") || beanName.endsWith("aspect") || beanName.endsWith("controller")
                            || beanName.endsWith("dao") || beanName.endsWith("datasource")
                            || beanName.endsWith("fallback") || beanDescriptor.getDependencies().length == 0) {
                        continue;
                    }
                    qualifiedBeans.put(entry1.getKey(), beanDescriptor);
                }
            }
            StringBuilder sb = new StringBuilder();
            cyclicDependence(qualifiedBeans, sb);
            if (sb.length() > 0) {
                sb.append(System.getProperty("line.separator"));
                sb.append("重注代码质量,尽量做到无循环依赖");
                sb.append(System.getProperty("line.separator"));
                sb.append("所属服务:" + serviceId);
                //alarmClient.sendByUser(Lists.newArrayList("zhangzhi"), sb.toString());
                alarmClient.sendByGroup("cf-server-alarm", sb.toString());
                end = System.currentTimeMillis();
            }
            log.info("checkCyclicDependence end,serviceid={},coust={}", serviceId, (end - start));
        }

    }

    public void cyclicDependence(Map<String, BeanDescriptor> beans, StringBuilder sb) {

        for (Map.Entry<String, BeanDescriptor> bean : beans.entrySet()) {
            String beanName = bean.getKey();
            check(beans, beanName, beanName, 0, sb);
        }
    }


    public void check(Map<String, BeanDescriptor> beans, String beanName, String dependenceName, int depth, StringBuilder sb) {
        if (depth == 4) {//这里可以指定深度，层级过多，容易栈溢出
            return;
        }
        depth++;
        BeanDescriptor bean = beans.get(dependenceName);//依赖项的依赖项
        if (bean != null) {
            String[] deps = bean.getDependencies();//依赖项
            for (String dep : deps) {
                if (dep.equals(beanName)) {
                    sb.append(System.getProperty("line.separator"));
                    String str = String.format("%s和%s存在循环依赖;", beanName, dependenceName);
                    sb.append(str);
                    log.info(str);
                } else {
                    check(beans, beanName, dep, depth, sb);
                }
            }
        }

    }
}

效果

我们在测试环境有个job 每隔几分钟巡检，有循环依赖就企业微信报警，这里截取一段日志，如下：

SpringCloud BeanCurrentlyInCreationException 异常解决方案-LMLPHP

最后

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要求：
1、具备较强的编程基本功，熟练掌握JAVA编程语言，熟悉常用数据结构与算法。
2、了解常用的开源框架和开源服务(Spring，Netty，MySQL，Redis，Tomcat，Nginx 等)。
3、熟悉网络编程、多线程编程、分布式等优先。
4、阅读过spring家族源码优先，有技术博客优先，熟悉spring-cloud技术栈优先。
5、做事积极主动，有较强的执行能力和和较好的沟通能力。

对水滴感兴趣的同学可找我内推，java 后端和QA 都可以，我找负责人评估合适的话，推给HR联系您。

zzhi.wang

SpringCloud BeanCurrentlyInCreationException 异常解决方案

前言

背景

1，本地模拟如下：

2，生产场景如下图：

异常排查&模拟

1，场景演示：

2，异常演示

3，解决异常

杜绝循环依赖的解决方案

1，查看bean的依赖

2，解析bean及其依赖beans

3，代码实现

效果

最后