SpingBoot错误信息处理及原理

2019/04/10 10:10
阅读数 4

SpringBoot错误信息处理机制

在一个web项目中,总需要对一些错误进行界面或者json数据返回,已实现更好的用户体验,SpringBoot中提供了对于错误处理的自动配置

ErrorMvcAutoConfiguration这个类存放了所有关于错误信息的自动配置。

1. SpringBoot处理错误请求的流程

访问步骤:

  • 首先客户端访问了错误界面。例:404或者500
  • SpringBoot注册错误请求/error。通过ErrorPageCustomizer组件实现
  • 通过BasicErrorController处理/error,对错误信息进行了自适应处理,浏览器会响应一个界面,其他端会响应一个json数据
  • 如果响应一个界面,通过DefaultErrorViewResolver类来进行具体的解析。可以通过模板引擎解析也可以解析静态资源文件,如果两者都不存在则直接返回默认的错误JSON或者错误View
  • 通过DefaultErrorAttributes来添加具体的错误信息

源代码

//错误信息的自动配置
public class ErrorMvcAutoConfiguration {
    //响应具体的错误信息
    @Bean
    public DefaultErrorAttributes errorAttributes() {
        return
    }
	//处理错误请求
    @Bean
    public BasicErrorController basicErrorController() {
        return 
    }
	//注册错误界面
    @Bean
    public ErrorMvcAutoConfiguration.ErrorPageCustomizer errorPageCustomizer() {
        return 
    }
//注册错误界面,错误界面的路径为/error
private static class ErrorPageCustomizer implements ErrorPageRegistrar, Ordered {
    //服务器基本配置
    private final ServerProperties properties;
    
	public void registerErrorPages(ErrorPageRegistry errorPageRegistry) {
        //获取服务器配置中的错误路径/error
            ErrorPage errorPage = new ErrorPage(this.dispatcherServletPath.getRelativePath(this.properties.getError().getPath()));
        //注册错误界面
            errorPageRegistry.addErrorPages(new ErrorPage[]{errorPage});
        }	
    
    //this.properties.getError()
public class ServerProperties{
    //错误信息的配置文件
    private final ErrorProperties error = new ErrorProperties();
}
   //getPath
public class ErrorProperties {
    @Value("${error.path:/error}")
    private String path = "/error";
//处理/error请求,从配置文件中取出请求的路径
@RequestMapping({"${server.error.path:${error.path:/error}}"})
public class BasicErrorController extends AbstractErrorController {
    
    //浏览器行为,通过请求头来判断,浏览器返回一个视图
    @RequestMapping(
        produces = {"text/html"}
 
    public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {
        HttpStatus status = this.getStatus(request);
        Map<String, Object> model = Collections.unmodifiableMap(this.getErrorAttributes(request, this.isIncludeStackTrace(request, MediaType.TEXT_HTML)));
        response.setStatus(status.value());
        ModelAndView modelAndView = this.resolveErrorView(request, response, status, model);
        return modelAndView != null ? modelAndView : new ModelAndView("error", model);
    }
	
    //其他客户端行为处理,返回一个JSON数据
    @RequestMapping
    public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) {
        HttpStatus status = this.getStatus(request);
        if (status == HttpStatus.NO_CONTENT) {
            return new ResponseEntity(status);
        } else {
            Map<String, Object> body = this.getErrorAttributes(request, this.isIncludeStackTrace(request, MediaType.ALL));
            return new ResponseEntity(body, status);
        }
    }
//添加错误信息
public class DefaultErrorAttributes implements ErrorAttributes, HandlerExceptionResolver, Ordered {
    public Map<String, Object> getErrorAttributes(WebRequest webRequest, boolean includeStackTrace) {
        Map<String, Object> errorAttributes = new LinkedHashMap();
        errorAttributes.put("timestamp", new Date());
        this.addStatus(errorAttributes, webRequest);
        this.addErrorDetails(errorAttributes, webRequest, includeStackTrace);
        this.addPath(errorAttributes, webRequest);
        return errorAttributes;
    }

2. 响应一个视图

步骤:

  • 客户端出现错误
  • SpringBoot创建错误请求/error
  • BasicErrorController处理请求
@RequestMapping(
        produces = {"text/html"}
    )
    public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {
        HttpStatus status = this.getStatus(request);
        Map<String, Object> model = Collections.unmodifiableMap(this.getErrorAttributes(request, this.isIncludeStackTrace(request, MediaType.TEXT_HTML)));
        response.setStatus(status.value());
        //解析错误界面,返回一个ModelAndView,调用父类AbstractErrorController的方法
        ModelAndView modelAndView = this.resolveErrorView(request, response, status, model);
        return modelAndView != null ? modelAndView : new ModelAndView("error", model);
    }
public abstract class AbstractErrorController{
     private final List<ErrorViewResolver> errorViewResolvers;
    
    protected ModelAndView resolveErrorView(HttpServletRequest request, HttpServletResponse response, HttpStatus status, Map<String, Object> model) {
        Iterator var5 = this.errorViewResolvers.iterator();
		//遍历所有的错误视图解析器
        ModelAndView modelAndView;
        do {
            if (!var5.hasNext()) {
                return null;
            }

            ErrorViewResolver resolver = (ErrorViewResolver)var5.next();
            //调用视图解析器的方法,
            modelAndView = resolver.resolveErrorView(request, status, model);
        } while(modelAndView == null);

        return modelAndView;
    }
}
public interface ErrorViewResolver {
    ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map<String, Object> model);
}
  • 处理具体的视图跳转
//处理视图跳转
public DefaultErrorViewResolver{
    public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map<String, Object> model) {
        //将状态码作为视图名称传入解析
        ModelAndView modelAndView = this.resolve(String.valueOf(status.value()), model);
        if (modelAndView == null && SERIES_VIEWS.containsKey(status.series())) {
            modelAndView = this.resolve((String)SERIES_VIEWS.get(status.series()), model);
        }

        return modelAndView;
    }
//视图名称为error文件夹下的400.html等状态码文件
  private ModelAndView resolve(String viewName, Map<String, Object> model) {
        String errorViewName = "error/" + viewName;
      //是否存在模板引擎进行解析
        TemplateAvailabilityProvider provider = this.templateAvailabilityProviders.getProvider(errorViewName, this.applicationContext);
      //存在则返回解析以后的数据,不存在调用resolveResource方法进行解析
        return provider != null ? new ModelAndView(errorViewName, model) : this.resolveResource(errorViewName, model);
    }  
    
    //如果静态资源文件中存在,返回静态文件下的,如果不存在返回SpringBoot默认的
    private ModelAndView resolveResource(String viewName, Map<String, Object> model) {
        String[] var3 = this.resourceProperties.getStaticLocations();
        int var4 = var3.length;

        for(int var5 = 0; var5 < var4; ++var5) {
            String location = var3[var5];

            try {
                Resource resource = this.applicationContext.getResource(location);
                resource = resource.createRelative(viewName + ".html");
                if (resource.exists()) {
                    return new ModelAndView(new DefaultErrorViewResolver.HtmlResourceView(resource), model);
                }
            } catch (Exception var8) {
            }
        }

        return null;
    }

应用:

  • 在模板引擎文件下创建error文件夹,里面放置各种状态码的视图文件,模板引擎会解析
  • 在静态资源下常见error文件夹,里面放置各种状态码的视图文件,模板引擎不会解析
  • 如果没有状态码文件,则返回springBoot默认界面视图

3.响应一个json数据

BasicErrorController处理/error请求的时候不适用浏览器默认请求

@RequestMapping
    public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) {
        HttpStatus status = this.getStatus(request);
        if (status == HttpStatus.NO_CONTENT) {
            return new ResponseEntity(status);
        } else {
            //调用父类的方法获取所有的错误属性
            Map<String, Object> body = this.getErrorAttributes(request, this.isIncludeStackTrace(request, MediaType.ALL));
            return new ResponseEntity(body, status);
        }
    }
父类方法:
protected Map<String, Object> getErrorAttributes(HttpServletRequest request, boolean includeStackTrace) {
        WebRequest webRequest = new ServletWebRequest(request);
        //调用ErrorAttributes接口的getErrorAttributes方法,
        return this.errorAttributes.getErrorAttributes(webRequest, includeStackTrace);
    }
添加错误信息
public class DefaultErrorAttributes{
    public Map<String, Object> getErrorAttributes(WebRequest webRequest, boolean includeStackTrace) {
        Map<String, Object> errorAttributes = new LinkedHashMap();
        errorAttributes.put("timestamp", new Date());
        this.addStatus(errorAttributes, webRequest);
        this.addErrorDetails(errorAttributes, webRequest, includeStackTrace);
        this.addPath(errorAttributes, webRequest);
        return errorAttributes;
    }

返回的json数据有:

  • status
  • error
  • exception
  • message
  • trace
  • path

可以通过模板引擎获取这些值

4.自定义异常返回自定义的异常数据

4.1@ControllerAdvice注解

SpringMVC提供的注解,可以用来定义全局异常,全局数据绑定,全局数据预处理

@ControllerAdivice定义全局的异常处理

  • 通过@ExceptionHandler(XXXException.class)执行该方法需要处理什么异常,然后返回什么数据或者视图
	//json数据返回	,处理自定义用户不存在异常
	@ResponseBody
    @ExceptionHandler(UserException.class)
    public Map<String,String> userExceptionMethod(UserException us){
        Map<String,String> map = new HashMap<>();
        map.put("message",us.getMessage());
        return map ;
    }

@ControllerAdvice定义全局数据

  • 通过@ModelAttribute(Name="key")定义全局数据的key
  • 默认方法的返回值的名称作为键
  • Controller中通过Model获取对应的key的值
@ControllerAdvice
public MyConfig{
	@ModelAttribute(name = "key")
    public Map<String,String> defineAttr(){
        Map<String,String> map = new HashMap<>();
        map.put("message","幻听");
        map.put("update","许嵩");
        return map ;
    }
    
@Controller
public UserController{
    @GetMapping("/hello")
    public Map<String, Object> hello(Model model){
        Map<String, Object> asMap = model.asMap();
        System.out.println(asMap);
        //{key={message='上山',update='左手一式太极拳'}}
        return asMap ;
    }
}

@ControllerAdvice处理预处理数据(当需要添加的实体,属性名字相同的时候)

  • Controller的参数中添加ModelAttribute作为属性赋值的前缀
  • ControllerAdvice修饰的类中,结合InitBinder来绑定对应的属性(该属性为ModelAttribite的value值
  • @InitBinder修饰的方法中通过WebDataBinder添加默认的前缀
@Getter@Setter
public class Book {
    private String name ;
    private int age ;
    
@Getter@Setter
public class Music {
    private String name ;
    private String author ;
    
    //这种方式的处理,spring无法判断Name属性给哪个bean赋值,所以需要通过别名的方式来进行赋值
@PostMapping("book")
    public String book(Book book , Music music){
        System.out.println(book);
        System.out.println(music);
        return "404" ;
    }
    //使用以下的方式
@PostMapping("/book")
    public String book(@ModelAttribute("b")Book book , @ModelAttribute("m")Music music){
        System.out.println(book);
        System.out.println(music);
        return "404" ;
    }
    
public MyCOnfiguration{
    @InitBinder("b")
    public void b(WebDataBinder webDataBinder){
        webDataBinder.setFieldDefaultPrefix("b.");
    }
    @InitBinder("m")
    public void m(WebDataBinder webDataBinder){
        webDataBinder.setFieldDefaultPrefix("m.");
    }
}
    

4.2自定义异常JSON

浏览器和其他客户端都只能获取json数据

@ControllerAdvice
public class MyExceptionHandler {

    //处理UserException异常
    @ResponseBody
    @ExceptionHandler(UserException.class)
    public Map<String,String> userExceptionMethod(UserException us){
        Map<String,String> map = new HashMap<>();
        map.put("message",us.getMessage());
        map.put("status","500");
        return map ;
    }

4.2自定义异常返回一个视图,拥有自适应效果

@ExceptionHandler(UserException.class)
    public String allException(UserException e,HttpServletRequest request){
        Map<String,String> map = new HashMap<>();
        map.put("message",e.getMessage());
        map.put("load","下山");
        request.setAttribute("myMessage",map);
        //设置状态码,SpringBoot通过java.servlet.error.status_code来设置状态码
        request.setAttribute("javax.servlet.error.status_code",400);
        return "forward:/error" ;
    }

当抛出UserException异常的时候,来到这个异常处理器,给这个请求中添加了数据,再转发到这个error请求中,交给ErrorPageCustomizer处理,由于设置了请求状态码400则返回的视图为400或4XX视图,或者直接返回一个JSON数据

{
    "timestamp": "2020-02-19T04:17:43.394+0000",
    "status": 400,
    "error": "Bad Request",
    "message": "用户名不存在异常",
    "path": "/crud/user/login"
}

  • 不足:JSON数据中没有显示我们自己定义的错误信息

4.3自定义错误信息

前面提到SpringBoot对错误信息的定义存在于DefaultErrorAttributes类的getErrorAttributes中,我们可以直接继承这个类,或者实现ErrorAttributes接口,然后将我们自己实现的错误处理器添加到容器中即可。

继承DefaultErrorAttributes和实现ErrorAttributes接口的区别是,继承以后仍然可以使用SpringBoot默认的错误信息,我们仅仅对该错误信息进行了增强;实现了ErrorAttributes接口,完全自定义错误信息

  • 实现ErrorAttributes接口
public class MyErrorHandler implements ErrorAttributes {
    
    public Map<String, Object> getErrorAttributes(WebRequest webRequest, boolean includeStackTrace) {
        Map<String, Object> errorAttributes = new LinkedHashMap();
        errorAttributes.put("timestamp", new Date());
        errorAttributes.put("status",500);
        errorAttributes.put("message","用户不存在异常");
        return errorAttributes;
    }

    @Override
    public Throwable getError(WebRequest webRequest) {
        return null;
    }
  • 继承DefaultErrorAttributes的方法
public class MyErrorHandler extends DefaultErrorAttributes {
    
    public Map<String, Object> getErrorAttributes(WebRequest webRequest, boolean includeStackTrace) {
        //调用父类方法,直接在默认错误信息的基础上添加
        Map<String, Object> errorAttributes = super.getErrorAttributes(webRequest,includeStackTrace);
        errorAttributes.put("timestamp", new Date());
        errorAttributes.put("message","用户不存在异常");
        return errorAttributes;
    }

}
  • 将定义的错误信息器添加到容器中
    • 通过@Component组件直接将MyErrorHandler组件添加到容器中
    • 通过@Bean在配置类中将组件添加到容器中
@Bean
    public DefaultErrorAttributes getErrorHandler(){
        return new MyErrorHandler();
    }
  • 下面解决上一节中没有出现我们自定义的异常信息
Map<String, Object> errorAttributes = super.getErrorAttributes(webRequest,includeStackTrace);
        errorAttributes.put("timestamp", new Date());
        errorAttributes.put("message","用户不存在异常");
        //指定从哪个作用域中取值
        webRequest.getAttribute("myMessage", RequestAttributes.SCOPE_REQUEST);
        return errorAttributes;

将在异常处理器中定义的错误信息取出,然后添加到错误信息中。

原文出处:https://www.cnblogs.com/onlyzuo/p/12330947.html

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