Spring boot异常处理机制

1、springboot默认错误处理机制

spring boot默认异常处理机制用浏览器请求时返回错误页面，其他应用请求时返回json数据。如下

编写控制器

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

/**
 * 测试
 *
 * @Author: Mr_li
 * @CreateDate: 2019-05-02 12:05
 * @Version: 1.0
 */
@Controller
public class TestController {

    @RequestMapping("/say")
    public String sayHi() {
        return "hi";
    }
}

浏览器请求

postman请求

页面能获取的信息：

timestamp：时间戳 
status：状态码 
error：错误提示 
exception：异常对象 
message：异常消息 
errors：JSR303数据校验的错误都在这里

2、springboot默认错误处理机制的实现

关键点在BasicErrorController这个类中

查看其实现

/*
 * Copyright 2012-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.boot.autoconfigure.web.servlet.error;

import java.util.Collections;
import java.util.List;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.boot.autoconfigure.web.ErrorProperties;
import org.springframework.boot.autoconfigure.web.ErrorProperties.IncludeStacktrace;
import org.springframework.boot.web.servlet.error.ErrorAttributes;
import org.springframework.boot.web.servlet.server.AbstractServletWebServerFactory;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.util.Assert;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;

/**
 * Basic global error {@link Controller}, rendering {@link ErrorAttributes}. More specific
 * errors can be handled either using Spring MVC abstractions (e.g.
 * {@code @ExceptionHandler}) or by adding servlet
 * {@link AbstractServletWebServerFactory#setErrorPages server error pages}.
 *
 * @author Dave Syer
 * @author Phillip Webb
 * @author Michael Stummvoll
 * @author Stephane Nicoll
 * @see ErrorAttributes
 * @see ErrorProperties
 */
@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {

	private final ErrorProperties errorProperties;

	/**
	 * Create a new {@link BasicErrorController} instance.
	 * @param errorAttributes the error attributes
	 * @param errorProperties configuration properties
	 */
	public BasicErrorController(ErrorAttributes errorAttributes,
			ErrorProperties errorProperties) {
		this(errorAttributes, errorProperties, Collections.emptyList());
	}

	/**
	 * Create a new {@link BasicErrorController} instance.
	 * @param errorAttributes the error attributes
	 * @param errorProperties configuration properties
	 * @param errorViewResolvers error view resolvers
	 */
	public BasicErrorController(ErrorAttributes errorAttributes,
			ErrorProperties errorProperties, List<ErrorViewResolver> errorViewResolvers) {
		super(errorAttributes, errorViewResolvers);
		Assert.notNull(errorProperties, "ErrorProperties must not be null");
		this.errorProperties = errorProperties;
	}

	@Override
	public String getErrorPath() {
		return this.errorProperties.getPath();
	}

        /**请求头为MediaType.TEXT_HTML_VALUE的执行这个返回页面*/
	@RequestMapping(produces = MediaType.TEXT_HTML_VALUE)
	public ModelAndView errorHtml(HttpServletRequest request,
			HttpServletResponse response) {
		HttpStatus status = getStatus(request);
		Map<String, Object> model = Collections.unmodifiableMap(getErrorAttributes(
				request, isIncludeStackTrace(request, MediaType.TEXT_HTML)));
		response.setStatus(status.value());
		ModelAndView modelAndView = resolveErrorView(request, response, status, model);
		return (modelAndView != null) ? modelAndView : new ModelAndView("error", model);
	}

        /**其他请求头返回obj*/
	@RequestMapping
	public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) {
		Map<String, Object> body = getErrorAttributes(request,
				isIncludeStackTrace(request, MediaType.ALL));
		HttpStatus status = getStatus(request);
		return new ResponseEntity<>(body, status);
	}

	/**
	 * Determine if the stacktrace attribute should be included.
	 * @param request the source request
	 * @param produces the media type produced (or {@code MediaType.ALL})
	 * @return if the stacktrace attribute should be included
	 */
	protected boolean isIncludeStackTrace(HttpServletRequest request,
			MediaType produces) {
		IncludeStacktrace include = getErrorProperties().getIncludeStacktrace();
		if (include == IncludeStacktrace.ALWAYS) {
			return true;
		}
		if (include == IncludeStacktrace.ON_TRACE_PARAM) {
			return getTraceParameter(request);
		}
		return false;
	}

	/**
	 * Provide access to the error properties.
	 * @return the error properties
	 */
	protected ErrorProperties getErrorProperties() {
		return this.errorProperties;
	}

}

发现它本身就是一个控制器，这个类是默认处理/error请求的。那么响应页面的时候是怎么找到页面的呢？

这里有一个关键类 DefaultErrorViewResolver

/*
 * Copyright 2012-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.boot.autoconfigure.web.servlet.error;

import java.util.Collections;
import java.util.EnumMap;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider;
import org.springframework.boot.autoconfigure.template.TemplateAvailabilityProviders;
import org.springframework.boot.autoconfigure.web.ResourceProperties;
import org.springframework.context.ApplicationContext;
import org.springframework.core.Ordered;
import org.springframework.core.io.Resource;
import org.springframework.http.HttpStatus;
import org.springframework.http.HttpStatus.Series;
import org.springframework.http.MediaType;
import org.springframework.util.Assert;
import org.springframework.util.FileCopyUtils;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.View;

/**
 * Default {@link ErrorViewResolver} implementation that attempts to resolve error views
 * using well known conventions. Will search for templates and static assets under
 * {@code '/error'} using the {@link HttpStatus status code} and the
 * {@link HttpStatus#series() status series}.
 * <p>
 * For example, an {@code HTTP 404} will search (in the specific order):
 * <ul>
 * <li>{@code '/<templates>/error/404.<ext>'}</li>
 * <li>{@code '/<static>/error/404.html'}</li>
 * <li>{@code '/<templates>/error/4xx.<ext>'}</li>
 * <li>{@code '/<static>/error/4xx.html'}</li>
 * </ul>
 *
 * @author Phillip Webb
 * @author Andy Wilkinson
 * @since 1.4.0
 */
public class DefaultErrorViewResolver implements ErrorViewResolver, Ordered {

	private static final Map<Series, String> SERIES_VIEWS;

	static {
		Map<Series, String> views = new EnumMap<>(Series.class);
		views.put(Series.CLIENT_ERROR, "4xx");
		views.put(Series.SERVER_ERROR, "5xx");
		SERIES_VIEWS = Collections.unmodifiableMap(views);
	}

	private ApplicationContext applicationContext;

	private final ResourceProperties resourceProperties;

	private final TemplateAvailabilityProviders templateAvailabilityProviders;

	private int order = Ordered.LOWEST_PRECEDENCE;

	/**
	 * Create a new {@link DefaultErrorViewResolver} instance.
	 * @param applicationContext the source application context
	 * @param resourceProperties resource properties
	 */
	public DefaultErrorViewResolver(ApplicationContext applicationContext,
			ResourceProperties resourceProperties) {
		Assert.notNull(applicationContext, "ApplicationContext must not be null");
		Assert.notNull(resourceProperties, "ResourceProperties must not be null");
		this.applicationContext = applicationContext;
		this.resourceProperties = resourceProperties;
		this.templateAvailabilityProviders = new TemplateAvailabilityProviders(
				applicationContext);
	}

	DefaultErrorViewResolver(ApplicationContext applicationContext,
			ResourceProperties resourceProperties,
			TemplateAvailabilityProviders templateAvailabilityProviders) {
		Assert.notNull(applicationContext, "ApplicationContext must not be null");
		Assert.notNull(resourceProperties, "ResourceProperties must not be null");
		this.applicationContext = applicationContext;
		this.resourceProperties = resourceProperties;
		this.templateAvailabilityProviders = templateAvailabilityProviders;
	}

	@Override
	public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status,
			Map<String, Object> model) {
		ModelAndView modelAndView = resolve(String.valueOf(status.value()), model);
		if (modelAndView == null && SERIES_VIEWS.containsKey(status.series())) {
			modelAndView = resolve(SERIES_VIEWS.get(status.series()), model);
		}
		return modelAndView;
	}

	private ModelAndView resolve(String viewName, Map<String, Object> model) {
                //默认去error下找且viewName作为视图名
		String errorViewName = "error/" + viewName;
		TemplateAvailabilityProvider provider = this.templateAvailabilityProviders
				.getProvider(errorViewName, this.applicationContext);
		if (provider != null) {
                        //模板引擎可用的时候返回配置的,默认为error/状态码.html。
			return new ModelAndView(errorViewName, model);
		}
                //返回默认的errorViewName下的
		return resolveResource(errorViewName, model);
	}

	private ModelAndView resolveResource(String viewName, Map<String, Object> model) {
		for (String location : this.resourceProperties.getStaticLocations()) {
			try {
				Resource resource = this.applicationContext.getResource(location);
				resource = resource.createRelative(viewName + ".html");
				if (resource.exists()) {
					return new ModelAndView(new HtmlResourceView(resource), model);
				}
			}
			catch (Exception ex) {
			}
		}
		return null;
	}

	@Override
	public int getOrder() {
		return this.order;
	}

	public void setOrder(int order) {
		this.order = order;
	}

	/**
	 * {@link View} backed by an HTML resource.
	 */
	private static class HtmlResourceView implements View {

		private Resource resource;

		HtmlResourceView(Resource resource) {
			this.resource = resource;
		}

		@Override
		public String getContentType() {
			return MediaType.TEXT_HTML_VALUE;
		}

		@Override
		public void render(Map<String, ?> model, HttpServletRequest request,
				HttpServletResponse response) throws Exception {
			response.setContentType(getContentType());
			FileCopyUtils.copy(this.resource.getInputStream(),
					response.getOutputStream());
		}

	}

}

一但系统出现4xx或者5xx之类的错误；

ErrorPageCustomizer就会生效（定制错误的响应规则）；

就会来到/error请求；

就会被BasicErrorController处理。

3、异常页面查找

创建一下目录

页面定义以及查找规则（默认）

如上图定义一个404的异常界面。访问一个不存在的页面（触发404）。查找顺序如下

1）有模板引擎的情况下；templates/error/状态码

将错误页面命名为 错误状态码.html 放在模板引擎文件夹里面的error文件夹下，发生此状态码的错误就会来到 对应的页面。

2）没有模板引擎（模板引擎找不到这个错误页面），静态资源文件夹下找(也就是static文件夹)； static/error/状态码

3）以上都没有错误页面，就是默认来到SpringBoot默认的错误提示页面

4、全局自定义异常处理

import com.example.demo.common.UserNotExistException;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.ResponseStatus;

import java.util.HashMap;
import java.util.Map;

/**
 * 全局异常捕获
 *
 * @Author: Mr_li
 * @CreateDate: 2019-05-02 15:07
 * @Version: 1.0
 */
@ControllerAdvice
public class MyExceptionHandler {

    @ResponseBody
    @ExceptionHandler(UserNotExistException.class)
    public Map<String, Object> handleException(Exception e) {
        Map<String, Object> map = new HashMap<>();
        map.put("code", "not_exist");
        map.put("message", e.getMessage());
        return map;
    }
}

@ControllerAdvice是controller的一个辅助类，最常用的就是作为全局异常处理的切面类
@ControllerAdvice可以指定扫描范围
@ControllerAdvice约定了几种可行的返回值，如果是直接返回model类的话，需要使用@ResponseBody进行json转换

返回String，表示跳到某个view
返回modelAndView
返回model + @ResponseBody （不加@ResponseBody）会抛出异常（would dispatch back to the current handler URL [/test1] again. Check your ViewResolver setup! (Hint: This may be the result of an unspecified view, due to default view name generation.)

创建自定义异常

import lombok.Data;

/**
 * 自定义异常
 *
 * @Author: Mr_li
 * @CreateDate: 2019-05-02 13:33
 * @Version: 1.0
 */
@Data
public class UserNotExistException extends RuntimeException {

    private String message;

    public UserNotExistException(String message) {
        super(message);
        this.message = message;
    }
}

创建控制器

import com.example.demo.common.UserNotExistException;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

import java.util.HashMap;
import java.util.Map;

/**
 * 测试
 *
 * @Author: Mr_li
 * @CreateDate: 2019-05-02 12:05
 * @Version: 1.0
 */
@Controller
public class TestController {

    @RequestMapping(value = "/test1")
    public void testException() {
        throw new UserNotExistException("用户不存在");
    }
}

执行结果