1. Introduction

1.绪论

Happy-path REST is pretty well-understood, and Spring makes this easy to do in Java.

Happy-path REST是很好理解的，Spring使其在Java中很容易做到。

But what about when things go wrong?

但当事情出错时怎么办？

In this tutorial, we’ll go over passing a Java exception as part of a JSON response using Spring.

在本教程中，我们将讨论使用Spring将Java异常作为JSON响应的一部分进行传递。

For a broader look, check out our posts on error handling for REST with Spring and creating a Java global exception handler.

如需更广泛的了解，请查看我们关于使用Spring的REST的错误处理和创建Java全局异常处理器的帖子。

2. An Annotated Solution

2.附加说明的解决方案

We’re going to use three basic Spring MVC annotations to solve this:

我们将使用三个基本的Spring MVC注解来解决这个问题。

@RestControllerAdvice which contains @ControllerAdvice to register the surrounding class as something each @Controller should be aware of, and @ResponseBody to tell Spring to render that method’s response as JSON
@ExceptionHandler to tell Spring which of our methods should be invoked for a given exception

Together, these create a Spring bean that handles any exceptions we configure it for. Here are more details about using @ControllerAdvice and @ExceptionHandler in conjunction.

这些一起创建了一个Spring Bean，可以处理我们配置的任何异常。这里有关于结合使用@ControllerAdvice和@ExceptionHandler的更多细节。

3. Example

3.例子

Firstly, let’s create an arbitrary custom exception to return to the client:

首先，让我们创建一个任意的自定义异常来返回给客户端。

public class CustomException extends RuntimeException {
    // constructors
}

Secondly, let’s define a class to handle the exception and pass it to the client as JSON:

其次，让我们定义一个类来处理异常，并将其作为JSON传递给客户端。

@RestControllerAdvice
public class ErrorHandler {

    @ExceptionHandler(CustomException.class)
    @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
    public CustomException handleCustomException(CustomException ce) {
        return ce;
    }

}

Note that we added the @ResponseStatus annotation. This will specify the status code to send to the client, in our case an Internal Server Error. Also, the @ResponseBody will ensure that the object is sent back to the client serialized in JSON. Finally, below is a dummy controller that shows an example of how the exception can be thrown:

注意，我们添加了@ResponseStatus 注释。这将指定发送至客户端的状态代码，在我们的例子中是内部服务器错误。此外，@ResponseBody将确保对象以JSON格式被发送回客户端。最后，下面是一个假的控制器，展示了一个如何抛出异常的例子。

@Controller
public class MainController {

    @GetMapping("/")
    public void index() throws CustomException {
        throw new CustomException();
    }

}

4. Conclusion

4.总结

In this post, we showed how to handle exceptions in Spring. Moreover, we showed how to send them back to the client serialized in JSON.

在这篇文章中，我们展示了如何在Spring中处理异常。此外，我们还展示了如何将它们以JSON的形式序列化地送回客户端。

The full implementation of this article can be found over on Github. This is a Maven-based project so it should be easy to import and run as it is.

本文的完整实现可以在Github上找到over。这是一个基于Maven的项目，所以应该很容易导入并按原样运行。