Spring - 解析统一数据格式返回以及统一异常处理

news2025/1/20 22:44:21

接上篇文章的统一数据格式返回…

文章目录

- 1. 统一异常处理
- - 1.1 使用
- 2. 统一数据返回和统一异处理是怎么实现的
- - 2.1 `initHandleAdapters`
  - 2.2 `initHandleExceptionResolvers`

1. 统一异常处理

1.1 使用

统一异常处理的两个关键的注解是@ControllerAdvice + @ExceptionHandler

@ControllerAdvice 表示控制器通知类
@ExceptionHandler:是异常处理器

两者结合就表示:出现异常的时候执行某个通知,也就是执行某个方法具体的代码如下:

@ControllerAdvice
@ResponseBody
public class ErrorAdvice {
    @ExceptionHandler
    public Object handleException(Exception e) {
        //表示代码如果出现Exception(及其之类)异常,就返回Result的对象
        return Result.fail(e.getMessage());
    }
}

其中Result是自定义的放回结果类:

同时,我们可以针对不同的异常,返回不同的结果

@ControllerAdvice
@ResponseBody
public class ErrorAdvice {
    @ExceptionHandler
    public Object handleException(Exception e) {
        //表示代码如果出现Exception(及其之类)异常,就返回Result的对象
        return Result.fail(e.getMessage());
    }

    @ExceptionHandler
    public Object handleException(ArithmeticException e) {
        return Result.fail("算术异常" + e.getMessage());
    }


    @ExceptionHandler
    public Object handleException(NullPointerException e) {
        return Result.fail("空指针异常" + e.getMessage());
    }
}

测试:

@RequestMapping("/test")
@RestController
public class TestController {
    @RequestMapping("/Test1")
    public String Test1() {
        int a = 10 / 0;
        return "t1";
    }


    @RequestMapping("Test2")
    public String Test2() {
        int[] arr = new int[4];
        int b = arr[4];
        return "t2";
    }
}

2. 统一数据返回和统一异处理是怎么实现的

统一数据返回和统一异处理是怎么实现的?
我们从DispatcherServlet的代码开始分析
当Tomcat启动的时候,有一个核心的类DispatcherServlet,用来控制程序的执行顺序
这个对象在创建的时候,会初始化一系列的对象:

其中与统一数据返回和统一异常处理相关的就是initHandleAdapters和initHandleExceptionResolvers

2.1 `initHandleAdapters`

这个⽅法在执时会查找使用所有的 @ControllerAdvice 类，把 ResponseBodyAdvice 类
放在容器中，当发⽣某个事件时，调⽤相应的Advice⽅法，⽐如返回数据前调⽤统⼀数据封装

private void initControllerAdviceCache() {
		if (getApplicationContext() == null) {
			return;
		}

    //查找所有被@ControllerAdvice注解的Bean
		List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());

		List<Object> requestResponseBodyAdviceBeans = new ArrayList<>();

		for (ControllerAdviceBean adviceBean : adviceBeans) {
			Class<?> beanType = adviceBean.getBeanType();
			if (beanType == null) {
				throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
			}
			Set<Method> attrMethods = MethodIntrospector.selectMethods(beanType, MODEL_ATTRIBUTE_METHODS);
			if (!attrMethods.isEmpty()) {
				this.modelAttributeAdviceCache.put(adviceBean, attrMethods);
			}
			Set<Method> binderMethods = MethodIntrospector.selectMethods(beanType, INIT_BINDER_METHODS);
			if (!binderMethods.isEmpty()) {
				this.initBinderAdviceCache.put(adviceBean, binderMethods);
			}

            //遍历adviceBeans列表，检查每个ControllerAdviceBean对应的bean类型是否实现了RequestBodyAdvice或ResponseBodyAdvice接口
			if (RequestBodyAdvice.class.isAssignableFrom(beanType) || ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
				requestResponseBodyAdviceBeans.add(adviceBean);
			}
		}

		if (!requestResponseBodyAdviceBeans.isEmpty()) {
			this.requestResponseBodyAdvice.addAll(0, requestResponseBodyAdviceBeans);
		}

		if (logger.isDebugEnabled()) {
			int modelSize = this.modelAttributeAdviceCache.size();
			int binderSize = this.initBinderAdviceCache.size();
			int reqCount = getBodyAdviceCount(RequestBodyAdvice.class);
			int resCount = getBodyAdviceCount(ResponseBodyAdvice.class);
			if (modelSize == 0 && binderSize == 0 && reqCount == 0 && resCount == 0) {
				logger.debug("ControllerAdvice beans: none");
			}
			else {
				logger.debug("ControllerAdvice beans: " + modelSize + " @ModelAttribute, " + binderSize +
						" @InitBinder, " + reqCount + " RequestBodyAdvice, " + resCount + " ResponseBodyAdvice");
			}
		}
	}

2.2 `initHandleExceptionResolvers`

initHandleExceptionResolvers方法会取得所有实现了HandleExceeptionResolver接口的Bean,其中就有一个ExceptionHandlerExceptionResolver 的bean,这个Bean在应用启动的时候或获取到所有被注解@ControllerAdvice标注的bean对象,做进一步处理

当Controller抛出异常的时候,DispatcherServlet使用ExceptionHandlerExceptionResolver 来解析异常,而ExceptionHandlerExceptionResolver 通过ExceptionHandlerMethodResolver 来解析异常

@Nullable
private Method getMappedMethod(Class<? extends Throwable> exceptionType) {
    List<Class<? extends Throwable>> matches = new ArrayList<>();
    for (Class<? extends Throwable> mappedException : this.mappedMethods.keySet()) {
        if (mappedException.isAssignableFrom(exceptionType)) {
            matches.add(mappedException);
        }
    }
    if (!matches.isEmpty()) {
        if (matches.size() > 1) {
            matches.sort(new ExceptionDepthComparator(exceptionType));
        }
        return this.mappedMethods.get(matches.get(0));
    }
    else {
        return NO_MATCHING_EXCEPTION_HANDLER_METHOD;
    }
}