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### 1. 使用 **@ControllerAdvice**和**@ExceptionHandler** 处理全局异常
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这是目前很常用的一种方式，非常推荐。测试代码中用到了 Junit 5，如果你新建项目验证下面的代码的话，记得添加上相关依赖。
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**1. 新建异常信息实体类**
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非必要的类，主要用于包装将异常信息。
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`src/main/java/com/twuc/webApp/exception/ErrorResponse.java`
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```java
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/**
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* @author shuang.kou
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*/
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public class ErrorResponse {
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private String message;
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private String errorTypeName;
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public ErrorResponse(Exception e) {
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this(e.getClass().getName(), e.getMessage());
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}
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public ErrorResponse(String errorTypeName, String message) {
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this.errorTypeName = errorTypeName;
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this.message = message;
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}
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......省略getter/setter方法
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}
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```
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**2. 自定义异常类型**
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`src/main/java/com/twuc/webApp/exception/ResourceNotFoundException.java`
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一般我们处理的都是 `RuntimeException` ，所以如果你需要自定义异常类型的话直接集成这个类就可以了。
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```java
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/**
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* @author shuang.kou
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* 自定义异常类型
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*/
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public class ResourceNotFoundException extends RuntimeException {
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private String message;
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public ResourceNotFoundException() {
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super();
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}
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public ResourceNotFoundException(String message) {
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super(message);
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this.message = message;
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}
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@Override
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public String getMessage() {
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return message;
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}
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public void setMessage(String message) {
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this.message = message;
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}
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}
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```
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**3. 新建异常处理类**
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我们只需要在类上加上`@ControllerAdvice`注解这个类就成为了全局异常处理类，当然你也可以通过 `assignableTypes `指定特定的类，让异常处理类只处理特定类抛出的异常。
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`src/main/java/com/twuc/webApp/exception/GlobalExceptionHandler.java`
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```java
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/**
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* @author shuang.kou
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*/
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@ControllerAdvice(assignableTypes = {ExceptionController.class})
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@ResponseBody
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public class GlobalExceptionHandler {
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ErrorResponse illegalArgumentResponse = new ErrorResponse(new IllegalArgumentException("参数错误!"));
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ErrorResponse resourseNotFoundResponse = new ErrorResponse(new ResourceNotFoundException("Sorry, the resourse not found!"));
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@ExceptionHandler(value = Exception.class)// 拦截所有异常, 这里只是为了演示，一般情况下一个方法特定处理一种异常
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public ResponseEntity<ErrorResponse> exceptionHandler(Exception e) {
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if (e instanceof IllegalArgumentException) {
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return ResponseEntity.status(400).body(illegalArgumentResponse);
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} else if (e instanceof ResourceNotFoundException) {
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return ResponseEntity.status(404).body(resourseNotFoundResponse);
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}
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return null;
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}
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}
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```
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**4. controller模拟抛出异常**
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`src/main/java/com/twuc/webApp/web/ExceptionController.java`
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```java
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/**
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* @author shuang.kou
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*/
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@RestController
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@RequestMapping("/api")
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public class ExceptionController {
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@GetMapping("/illegalArgumentException")
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public void throwException() {
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throw new IllegalArgumentException();
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}
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@GetMapping("/resourceNotFoundException")
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public void throwException2() {
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throw new ResourceNotFoundException();
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}
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}
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```
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使用 Get 请求 [localhost:8080/api/resourceNotFoundException](localhost:8333/api/resourceNotFoundException) （curl -i -s -X GET url），服务端返回的 JSON 数据如下：
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```json
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{
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"message": "Sorry, the resourse not found!",
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"errorTypeName": "com.twuc.webApp.exception.ResourceNotFoundException"
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}
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```
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**5. 编写测试类**
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MockMvc 由`org.springframework.boot.test`包提供，实现了对Http请求的模拟，一般用于我们测试 controller 层。
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```java
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/**
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* @author shuang.kou
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*/
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@AutoConfigureMockMvc
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@SpringBootTest
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public class ExceptionTest {
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@Autowired
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MockMvc mockMvc;
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@Test
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void should_return_400_if_param_not_valid() throws Exception {
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mockMvc.perform(get("/api/illegalArgumentException"))
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.andExpect(status().is(400))
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.andExpect(jsonPath("$.message").value("参数错误!"));
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}
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@Test
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void should_return_404_if_resourse_not_found() throws Exception {
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mockMvc.perform(get("/api/resourceNotFoundException"))
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.andExpect(status().is(404))
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.andExpect(jsonPath("$.message").value("Sorry, the resourse not found!"));
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}
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}
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```
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### 2. @ExceptionHandler 处理 Controller 级别的异常
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我们刚刚也说了使用`@ControllerAdvice`注解 可以通过 `assignableTypes `指定特定的类，让异常处理类只处理特定类抛出的异常。所以这种处理异常的方式，实际上现在使用的比较少了。
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我们把下面这段代码移到 `src/main/java/com/twuc/webApp/exception/GlobalExceptionHandler.java` 中就可以了。
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```java
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@ExceptionHandler(value = Exception.class)// 拦截所有异常
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public ResponseEntity<ErrorResponse> exceptionHandler(Exception e) {
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if (e instanceof IllegalArgumentException) {
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return ResponseEntity.status(400).body(illegalArgumentResponse);
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} else if (e instanceof ResourceNotFoundException) {
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return ResponseEntity.status(404).body(resourseNotFoundResponse);
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}
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return null;
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}
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```
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### 3. ResponseStatusException
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研究 ResponseStatusException 我们先来看看，通过 `ResponseStatus`注解简单处理异常的方法。
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`src/main/java/com/twuc/webApp/exception/ResourceNotFoundException.java`
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```java
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@ResponseStatus(code = HttpStatus.NOT_FOUND)
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public class ResourseNotFoundException2 extends RuntimeException {
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public ResourseNotFoundException2() {
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}
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public ResourseNotFoundException2(String message) {
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super(message);
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}
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}
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```
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`src/main/java/com/twuc/webApp/web/ResponseStatusExceptionController.java`
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```java
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@RestController
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@RequestMapping("/api")
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public class ResponseStatusExceptionController {
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@GetMapping("/resourceNotFoundException2")
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public void throwException3() {
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throw new ResourseNotFoundException2("Sorry, the resourse not found!");
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}
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}
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```
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使用 Get 请求 [localhost:8080/api/resourceNotFoundException2](localhost:8333/api/resourceNotFoundException2) ，服务端返回的 JSON 数据如下：
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```json
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{
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"timestamp": "2019-08-21T07:11:43.744+0000",
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"status": 404,
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"error": "Not Found",
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"message": "Sorry, the resourse not found!",
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"path": "/api/resourceNotFoundException2"
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}
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```
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这种通过 `ResponseStatus`注解简单处理异常的方法是的好处是比较简单，但是一般我们不会这样做，通过`ResponseStatusException`会更加方便,可以避免我们额外的异常类。
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```java
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@GetMapping("/resourceNotFoundException2")
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public void throwException3() {
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throw new ResponseStatusException(HttpStatus.NOT_FOUND, "Sorry, the resourse not found!", new ResourceNotFoundException());
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}
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```
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使用 Get 请求 [localhost:8080/api/resourceNotFoundException2](localhost:8333/api/resourceNotFoundException2) ，服务端返回的 JSON 数据如下,和使用 `ResponseStatus` 实现的效果一样：
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```json
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{
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"timestamp": "2019-08-21T07:28:12.017+0000",
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"status": 404,
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"error": "Not Found",
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"message": "Sorry, the resourse not found!",
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"path": "/api/resourceNotFoundException3"
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}
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```
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`ResponseStatusException` 提供了三个构造方法：
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```java
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public ResponseStatusException(HttpStatus status) {
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this(status, null, null);
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}
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public ResponseStatusException(HttpStatus status, @Nullable String reason) {
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this(status, reason, null);
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}
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public ResponseStatusException(HttpStatus status, @Nullable String reason, @Nullable Throwable cause) {
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super(null, cause);
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Assert.notNull(status, "HttpStatus is required");
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this.status = status;
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this.reason = reason;
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}
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```
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构造函数中的参数解释如下：
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- status ： http status
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- reason ：response 的消息内容
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- cause ： 抛出的异常

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