Spring Boot 自定义FailureAnalyzer

今天在学习Spring Boot 源码的过程中，在spring.factories 文件中无意中发现了FailureAnalyzer 这个接口。由于之前没有接触过，今天来学习一下 FailureAnalyzer 接口的作用。

在学习FailureAnalyzer之前, 我们先看以下截图

相信Spring的开发者，或多或少的遇到过以上的错误。由于端口占用阻止了应用程序启动，这跟今天的主角有关系。Spring Boot 应用程序启动时，FailureAnalyzer接口拦截启动过程中发生的异常，并终止启动。

FailureAnalyzer

核心接口定义

package org.springframework.boot.diagnostics;
/*** 该接口用户分析异常堆栈信息，将其转换为用户可读的对象信息，通常情况下，对象包含错误描述和建议.* @author Andy Wilkinson* @since 1.4.0*/
@FunctionalInterface
public interface FailureAnalyzer {/*** 返回异常错误的分析对象，或null* @param failure the failure* @return the analysis or {@code null}*/FailureAnalysis analyze(Throwable failure);
}

FailureAnalyzer 定义为函数式接口，因此可以使用Lambda表达式实现接口，简化代码开发。从定义上可以看出接收 Throwable 类型的参数，返回失败分析对象 - FailureAnalysis

FailureAnalysis 对象

package org.springframework.boot.diagnostics;/*** The result of analyzing a failure.** @author Andy Wilkinson* @since 1.4.0*/
public class FailureAnalysis {// 问题描述private final String description;// 动作(解决问题的方法)private final String action;// 问题原因private final Throwable cause;public FailureAnalysis(String description, String action, Throwable cause) {this.description = description;this.action = action;this.cause = cause;}// get 方法...
}

PortInUseFailureAnalyzer

以文章开头的报错信息为例，PortInUseFailureAnalyzer 继承AbstractFailureAnalyzer抽象类，最终实现了端口占用报错信息的分析。

package org.springframework.boot.diagnostics.analyzer;import org.springframework.boot.diagnostics.AbstractFailureAnalyzer;
import org.springframework.boot.diagnostics.FailureAnalysis;
import org.springframework.boot.web.server.PortInUseException;class PortInUseFailureAnalyzer extends AbstractFailureAnalyzer {@Overrideprotected FailureAnalysis analyze(Throwable rootFailure, PortInUseException cause) {return new FailureAnalysis("Web server failed to start. Port " + cause.getPort() + " was already in use.","Identify and stop the process that's listening on port " + cause.getPort() + " or configure this "+ "application to listen on another port.",cause);}
}

AbstractFailureAnalyzer

public abstract class AbstractFailureAnalyzer implements FailureAnalyzer {@Overridepublic FailureAnalysis analyze(Throwable failure) {T cause = findCause(failure, getCauseType());return (cause != null) ? analyze(failure, cause) : null;}/*** 重新定义钩子方法，将参数与泛型对象关联，具象化了每一个子类需要实现的功能*/protected abstract FailureAnalysis analyze(Throwable rootFailure, T cause);@SuppressWarnings("unchecked")protected Class getCauseType() {return (Class) ResolvableType.forClass(AbstractFailureAnalyzer.class, getClass()).resolveGeneric();}@SuppressWarnings("unchecked")protected final  E findCause(Throwable failure, Class type) {while (failure != null) {if (type.isInstance(failure)) {return (E) failure;}failure = failure.getCause();}return null;}
}

FailureAnalyzer接口的核心抽象类，并重新扩展了FailureAnalyzer接口定义的功能。该抽象类实现了Exception对象与失败分析实现类一一对应的功能。如

//PortInUseFailureAnalyzer 负责解析 PortInUseException 异常
class PortInUseFailureAnalyzer extends AbstractFailureAnalyzer{...
}

FailureAnalyzer-自定义

上面提到过具体的失败分析类，是跟每一种Exception类对应的，那么我们从定义异常类开始

定义异常类

package com.andy.spring.boot.docker.exception;public class CustomApplicationException extends RuntimeException {public CustomApplicationException(String msg){super(msg);}
}

异常类定义完毕后，需要定义解析该异常的失败分析类

实现FailureAnalyzer

package com.andy.spring.boot.docker.analyzer;import com.andy.spring.boot.docker.exception.CustomApplicationException;
import org.springframework.boot.diagnostics.AbstractFailureAnalyzer;
import org.springframework.boot.diagnostics.FailureAnalysis;public class CustomApplicationFailureAnalyzer extends AbstractFailureAnalyzer {@Overrideprotected FailureAnalysis analyze(Throwable rootFailure, CustomApplicationException cause) {return new FailureAnalysis("Yeah, 自定义失败分析器出现了...!","Ummm... 啥都不做，删库跑路",cause);}
}

接下来，需要Spring

添加spring.factories

接下来，需要Spring Boot 框架识别失败分析。SPI机制出场，在resources/META-INF目录下创建spring.factories文件，内容如下

org.springframework.boot.diagnostics.FailureAnalyzer=com.andy.spring.boot.docker.analyzer.CustomApplicationFailureAnalyzer

验证测试

测试代码

到目前为止，万事具备，只欠东风。我们需要在应用启动时，抛出自定义异常即可

package com.andy.spring.boot.docker.service;import com.andy.spring.boot.docker.exception.CustomApplicationException;
import org.springframework.stereotype.Component;@Component
public class CacheService {public CacheService() {throw new CustomApplicationException("bean 初始化异常");}}

验证结果

重新启动应用程序，出现以下错误