1. Overview

1.概述

A FailureAnalyzer in Spring Boot offers a way to intercept exceptions that occur during the startup of an application causing an application startup failure.

Spring Boot中的FailureAnalyzer提供了一种方法，可以拦截应用程序启动过程中发生的异常，导致应用程序启动失败。

The FailureAnalyzer replaces the stack trace of the exception with a more readable message represented by a FailureAnalysis object that contains a description of the error and a suggested course of action.

FailureAnalyzer用一个FailureAnalysis对象代表的更易读的消息取代了异常的堆栈跟踪，该对象包含错误的描述和建议的行动方案。

Boot contains a series of analyzers for common startup exceptions such as PortInUseException, NoUniqueBeanDefinitionException, and UnsatisfiedDependencyException. These can be found in the org.springframework.boot.diagnostics package.

Boot包含一系列针对常见启动异常的分析器，如PortInUseException、NoUniqueBeanDefinitionException和UnsatisfiedDependencyException。这些可以在org.springframework.boot.diagnostics包中找到。

In this quick tutorial, we’re going to take a look at how we can add our own custom FailureAnalyzer to the existing ones.

在这个快速教程中，我们将看看如何在现有的FailureAnalyzer中添加我们自己的自定义FailureAnalyzer。

2. Creating a Custom FailureAnalyzer

2.创建一个自定义的FailureAnalyzer

To create a custom FailureAnalyzer, we’ll simply extend the abstract class AbstractFailureAnalyzer – which intercepts a specified exception type and implement analyze() API.

为了创建一个自定义的FailureAnalyzer，我们将简单地扩展抽象类AbstractFailureAnalyzer–它拦截一个指定的异常类型并实现analyze() API。

The framework provides a BeanNotOfRequiredTypeFailureAnalyzer implementation that deals with the exception BeanNotOfRequiredTypeException only if the bean being injected is of a dynamic proxy class.

该框架提供了一个BeanNotOfRequiredTypeFailureAnalyzer实现，该实现只在被注入的Bean是动态代理类时处理异常BeanNotOfRequiredTypeException。

Let’s create a custom FailureAnalyzer that deals with all exceptions of type BeanNotOfRequiredTypeException. Our class intercepts the exception and creates a FailureAnalysis object with helpful description and action messages:

让我们创建一个自定义的FailureAnalyzer，处理所有BeanNotOfRequiredTypeException类型的异常。我们的类拦截异常，并创建一个FailureAnalysis对象，其中包含有用的描述和操作信息。

public class MyBeanNotOfRequiredTypeFailureAnalyzer 
  extends AbstractFailureAnalyzer<BeanNotOfRequiredTypeException> {

    @Override
    protected FailureAnalysis analyze(Throwable rootFailure, 
      BeanNotOfRequiredTypeException cause) {
        return new FailureAnalysis(getDescription(cause), getAction(cause), cause);
    }

    private String getDescription(BeanNotOfRequiredTypeException ex) {
        return String.format("The bean %s could not be injected as %s "
          + "because it is of type %s",
          ex.getBeanName(),
          ex.getRequiredType().getName(),
          ex.getActualType().getName());
    }

    private String getAction(BeanNotOfRequiredTypeException ex) {
        return String.format("Consider creating a bean with name %s of type %s",
          ex.getBeanName(),
          ex.getRequiredType().getName());
    }
}

3. Registering the Custom FailureAnalyzer

3.注册自定义FailureAnalyzer

For the custom FailureAnalyzer to be considered by Spring Boot, it is mandatory to register it in a standard resources/META-INF/spring.factories file that contains the org.springframework.boot.diagnostics.FailureAnalyzer key with a value of the full name of our class:

为了使自定义的FailureAnalyzer被Spring Boot考虑，必须在标准的resources/META-INF/spring.plants文件中注册，该文件包含org.springframework.boot.diagnostics.FailureAnalyzer键，其值为我们类的全名。

org.springframework.boot.diagnostics.FailureAnalyzer=\
  com.baeldung.failureanalyzer.MyBeanNotOfRequiredTypeFailureAnalyzer

**4. Custom FailureAnalyzer in Action**

**4.自定义FailureAnalyzer的操作**

Let’s create a very simple example in which we attempt to inject a bean of an incorrect type to see how our custom FailureAnalyzer behaves.

让我们创建一个非常简单的例子，我们试图注入一个不正确类型的Bean，看看我们的自定义FailureAnalyzer是如何表现的。

Let’s create two classes MyDAO and MySecondDAO and annotate the second class as a bean called myDAO:

让我们创建两个类MyDAO和MySecondDAO，并将第二个类注释为名为myDAO的bean。

public class MyDAO { }

@Repository("myDAO")
public class MySecondDAO { }

Next, in a MyService class, we will attempt to inject the myDAO bean, which is of type MySecondDAO, into a variable of type MyDAO:

接下来，在MyService类中，我们将尝试把myDAObean（其类型为MySecondDAO）注入到MyDAO类型的变量。

@Service
public class MyService {

    @Resource(name = "myDAO")
    private MyDAO myDAO;
}

Upon running the Spring Boot application, the startup will fail with the following console output:

运行Spring Boot应用程序时，启动将失败，控制台输出如下。

***************************
APPLICATION FAILED TO START
***************************

Description:

The bean myDAO could not be injected as com.baeldung.failureanalyzer.MyDAO 
  because it is of type com.baeldung.failureanalyzer.MySecondDAO$$EnhancerBySpringCGLIB$$d902559e

Action:

Consider creating a bean with name myDAO of type com.baeldung.failureanalyzer.MyDAO

5. Conclusion

5.结论

In this quick tutorial, we’ve focused on how implementing a custom Spring Boot FailureAnalyzer.

在这个快速教程中，我们重点介绍了如何实现一个自定义的Spring Boot FailureAnalyzer。

As always, the full source code of the example can be found over on GitHub.

一如既往，该示例的完整源代码可以在GitHub上找到over。