Springboot错误处理机制实现原理解析

{
  "timestamp": "2020-03-24T02:49:56.572+0000",
  "status": 404,
  "error": "Not Found",
  "message": "No message available",
  "path": "/"
}

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;
}

@RequestMapping(
    produces = {"text/html"}
  )
  public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {
    HttpStatus status = this.getStatus(request);
    //处理页面的请求返回给前台数据 model 的获取 ，调用
    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);
  }
 
 
 
//调用 AbstractErrorController#getErrorAttributes
  protected Map<String, Object> getErrorAttributes(HttpServletRequest request, boolean includeStackTrace) {
    WebRequest webRequest = new ServletWebRequest(request);
    return this.errorAttributes.getErrorAttributes(webRequest, includeStackTrace);
  }
 
 
 
最终调用DefaultErrorAttributes#getErrorAttributes
  public Map<String, Object> getErrorAttributes(WebRequest webRequest, boolean includeStackTrace) {

@Controller
@RequestMapping({"${server.error.path:${error.path:/error}}"}) 
public class BasicErrorController extends AbstractErrorController {
  private final ErrorProperties errorProperties;
public String getErrorPath() {
  return this.errorProperties.getPath();
}

@RequestMapping(
  produces = {"text/html"}  //产生html类型的数据，浏览器发送的请求来到这个方法处理
)
public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {
　　//获取状态码
  HttpStatus status = this.getStatus(request);
　　//获取模型数据
  Map<String, Object> model = Collections.unmodifiableMap(this.getErrorAttributes(request, this.isIncludeStackTrace(request, MediaType.TEXT_HTML)));
  response.setStatus(status.value());
　　//去哪个页面作为错误页面，包括页面地址和内容
  ModelAndView modelAndView = this.resolveErrorView(request, response, status, model);
  return modelAndView != null ? modelAndView : new ModelAndView("error", model);
}

@RequestMapping //产生json类型的数据， 其他客户端发送的请求来到这个方法处理
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);
  }
}

public class ErrorProperties {
  @Value("${error.path:/error}")
  private String path = "/error";  //系统出现错误请求之后来到 /error 请求进行处理 ，（类似于以前 web.xml 中注册的错误页面规则）

public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map<String, Object> model) {
    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;
  }
 
  private ModelAndView resolve(String viewName, Map<String, Object> model) {　　　　//默认 springboot 可以找到这个页面 error/404
    String errorViewName = "error/" + viewName;　　　　//模板引擎可以解析这个页面地址就用模板引擎解析
    TemplateAvailabilityProvider provider = this.templateAvailabilityProviders.getProvider(errorViewName, this.applicationContext);　　　　//模板引擎可用的情况下就返回到 errorViewName 指定的视图地址
    return provider != null ? new ModelAndView(errorViewName, model) : this.resolveResource(errorViewName, model);
  }
　  //模板引擎不可用就在静态资源文件夹里面找 errorViewName 对应的页面  error/404.html
  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");　　　　　　　　　　//如果静态资源文件中由 这个资源就直接使用，否则返回为空
        if (resource.exists()) {
          return new ModelAndView(new DefaultErrorViewResolver.HtmlResourceView(resource), model);
        }
      } catch (Exception var8) {
      }
    }
　　　　　
    return null;
  }

protected ModelAndView resolveErrorView(HttpServletRequest request, HttpServletResponse response, HttpStatus status, Map<String, Object> model) {
  Iterator var5 = this.errorViewResolvers.iterator();　　　　　//解析所有的 ErrorViewResolver 得到 modelAndView
  ModelAndView modelAndView;
  do {
    if (!var5.hasNext()) {
      return null;
    }
    ErrorViewResolver resolver = (ErrorViewResolver)var5.next();
    modelAndView = resolver.resolveErrorView(request, status, model);
  } while(modelAndView == null);
  return modelAndView;
}

@ControllerAdvice
public class MyExceptionHandler {
 
  @ResponseBody
  @ExceptionHandler(UserNotExistException.class)
  public Map<String,Object> handleException(Exception e){
    Map<String,Object> map = new HashMap<>();
    map.put("code","user.notexist");
    map.put("message",e.getMessage());
    return map;
  }
}
//通过异常处理器，但没有自适应效果（浏览器返回页面，客户端访问返回json数据）

@RequestMapping(
  produces = {"text/html"}
)
public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {　　　　　//获取错误的状态码，在分析的过程中，要注意参数从哪儿来？  =======》前领导的一句话，哈哈……
  HttpStatus status = this.getStatus(request);
  Map<String, Object> model = Collections.unmodifiableMap(this.getErrorAttributes(request, this.isIncludeStackTrace(request, MediaType.TEXT_HTML)));
  response.setStatus(status.value());　　　　//依据错误状态码解析错误试图，如果直接转发，不指定错误状态码则试图解析出错（直接转发状态码为 200 ，到不了定制的 4xx 5xx 的页面）
  ModelAndView modelAndView = this.resolveErrorView(request, response, status, model);
  return modelAndView != null ? modelAndView : new ModelAndView("error", model);
}

@ExceptionHandler(UserNotExistException.class)
  public String handleException(Exception e, HttpServletRequest request){
    Map<String,Object> map = new HashMap<>();
    <strong>//传入我们自己的错误状态码 4xx 5xx，否则就不会进入定制错误页面的解析流程</strong>
    /**
     * Integer statusCode = (Integer) request
     .getAttribute("javax.servlet.error.status_code");
     */
    request.setAttribute("javax.servlet.error.status_code",500);
    map.put("code","user.notexist");
    map.put("message",e.getMessage());
    //转发到/error
    return "forward:/error";
  }

//给容器中加入我们自己定义的ErrorAttributes
@Component
public class MyErrorAttributes extends DefaultErrorAttributes {
 
  @Override
  public Map<String, Object> getErrorAttributes(RequestAttributes requestAttributes, boolean includeStackTrace) {
    Map<String, Object> map = super.getErrorAttributes(requestAttributes, includeStackTrace);
    map.put("company","atguigu");
    return map;
  }
}