Spring MVC入门（九）：拦截器

拦截器

• 简介

SpringMVC中的拦截器用于拦截控制器方法的执行
SpringMVC中的拦截器需要实现HandlerInterceptor

• 拦截器中的3个抽象方法

# 浏览器  ->  filter  ->  DispatcherServlet  ->  controller
# preHandle方法则是在controller执行前执行

preHandle：控制器方法执行之前执行preHandle()，其boolean类型的返回值表示是否拦截或放行，返回true为放行，即调用控制器方法；返回false表示拦截，即不调用控制器方法
postHandle：控制器方法执行之后执行postHandle()
afterComplation：处理完视图和模型数据，渲染视图完毕之后执行afterComplation()

• 查看源码

# 双击shift，搜索DispatcherServlet，点击右上角的下载源码，查看DispatcherServlet.java
# 查看1061行

// 调用所有的拦截器preHandle方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
    return;
}

// 调用控制器的方法
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

if (asyncManager.isConcurrentHandlingStarted()) {
    return;
}

// 调用所有所有拦截器的postHandle方法
applyDefaultViewName(processedRequest, mv);
    mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
    dispatchException = ex;
}
catch (Throwable err) {
    // As of 4.3, we're processing Errors thrown from handler methods as well,
    // making them available for @ExceptionHandler methods and other scenarios.
    dispatchException = new NestedServletException("Handler dispatch failed", err);      // 这个方法中有渲染视图的方法，ctrl查看
}

# 查看processDispatchResult方法，在方法的最下面，也即是视图渲染完后会执行afterComplation方法
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);

	private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {

		boolean errorView = false;

		if (exception != null) {
			if (exception instanceof ModelAndViewDefiningException) {
				logger.debug("ModelAndViewDefiningException encountered", exception);
				mv = ((ModelAndViewDefiningException) exception).getModelAndView();
			}
			else {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				mv = processHandlerException(request, response, handler, exception);
				errorView = (mv != null);
			}
		}

		// Did the handler return a view to render?
		if (mv != null && !mv.wasCleared()) {
			render(mv, request, response);
			if (errorView) {
				WebUtils.clearErrorRequestAttributes(request);
			}
		}
		else {
			if (logger.isTraceEnabled()) {
				logger.trace("No view rendering, null ModelAndView returned.");
			}
		}

		if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
			// Concurrent handling started during a forward
			return;
		}

		if (mappedHandler != null) {
			// Exception (if any) is already handled..
			mappedHandler.triggerAfterCompletion(request, response, null);
		}
	}

• 代码案例1

# springmvc配置文件中配置视图控制器，用于跳转到index.html
<mvc:view-controller path="/" view-name="index"></mvc:view-controller>

# springmvc配置文件中配置拦截器
<mvc:interceptors>
    <bean class="com.atguigu.mvc.interceptors.FirstInterceptor"></bean>
</mvc:interceptors>

# 编写1个控制器，用于测试
@Controller
public class TestController {

    @RequestMapping("/**/testInterceptor")
    public String testInterceptor(){
        return "success";
    }

}

# 编写1个拦截器
@Component
public class FirstInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("FirstInterceptor-->preHandle");
        // 为true表示放行
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("FirstInterceptor-->postHandle");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("FirstInterceptor-->afterCompletion");
    }
}

# 测试
http://localhost:8080/上下文路径/testInterceptor
# 控制台打印
FirstInterceptor-->preHandle
FirstInterceptor-->postHandle
FirstInterceptor-->afterCompletion

# 如果将拦截器中的preHandle方法改为不放行
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("FirstInterceptor-->preHandle");
        // 为false表示不放行
        return false;
    }
# 再次测试，控制台打印如下
FirstInterceptor-->preHandle
# 这是因为访问testInterceptor接口时，被拦截了，后面的postHandle方法和afterCompletion方法就不会执行了

• 代码案例2

# springmvc配置文件中配置拦截器，如下方式，会拦截所有请求
<mvc:interceptors>
    <bean class="com.atguigu.mvc.interceptors.FirstInterceptor"></bean>
</mvc:interceptors>

# 编写1个控制器，用于测试
@Controller
public class TestController {

    @RequestMapping("/**/testInterceptor")
    public String testInterceptor(){
        return "success";
    }

}

# 编写1个拦截器
@Component
public class FirstInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("FirstInterceptor-->preHandle");
        // 为true表示放行
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("FirstInterceptor-->postHandle");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("FirstInterceptor-->afterCompletion");
    }
}

# 测试
http://localhost:8080/上下文路径/testInterceptor
# 控制台打印
FirstInterceptor-->preHandle
FirstInterceptor-->postHandle
FirstInterceptor-->afterCompletion

• 代码案例3

# 拦截器FirstInterceptor添加注解@Component，将其注册为1个bean

# springmvc配置文件中开启组件扫描，确保拦截器能够被扫描到
<context:component-scan base-package="com.atguigu.mvc"></context:component-scan>

# springmvc配置文件中配置拦截器，如下方式，会拦截所有请求
<mvc:interceptors>
    <ref bean="firstInterceptor"></ref>
</mvc:interceptors>

# 编写1个控制器，用于测试
@Controller
public class TestController {

    @RequestMapping("/**/testInterceptor")
    public String testInterceptor(){
        return "success";
    }

}

# 编写1个拦截器
@Component
public class FirstInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("FirstInterceptor-->preHandle");
        // 为true表示放行
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("FirstInterceptor-->postHandle");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("FirstInterceptor-->afterCompletion");
    }
}

# 测试
http://localhost:8080/上下文路径/testInterceptor
# 控制台打印
FirstInterceptor-->preHandle
FirstInterceptor-->postHandle
FirstInterceptor-->afterCompletion

• 代码案例4

# 拦截器FirstInterceptor添加注解@Component，将其注册为1个bean

# springmvc配置文件中开启组件扫描，确保拦截器能够被扫描到
<context:component-scan base-package="com.atguigu.mvc"></context:component-scan>

# springmvc配置文件中配置拦截器，如下方式，会拦截指定请求
<mvc:interceptors>
        <mvc:interceptor>
            <!-- 表示拦截一级目录的所有请求 -->
            <mvc:mapping path="/*"/>
            <!-- 表示放行该请求 -->
            <mvc:exclude-mapping path="/"/>
            <ref bean="firstInterceptor"></ref>
        </mvc:interceptor>
</mvc:interceptors>

# 编写1个控制器，用于测试
@Controller
public class TestController {

    @RequestMapping("/**/testInterceptor")
    public String testInterceptor(){
        return "success";
    }

}

# 编写1个拦截器
@Component
public class FirstInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("FirstInterceptor-->preHandle");
        // 为true表示放行
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("FirstInterceptor-->postHandle");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("FirstInterceptor-->afterCompletion");
    }
}

# 测试
http://localhost:8080/上下文路径/
# 控制台打印没有打印，说明指定的根路径被放行了

# 测试
http://localhost:8080/上下文路径/testInterceptor
# 控制台打印
FirstInterceptor-->preHandle
FirstInterceptor-->postHandle
FirstInterceptor-->afterCompletion

# 测试二级目录
http://localhost:8080/上下文路径/test/testInterceptor
# 控制台打印没有打印说明没有拦截

• 代码案例5

# 拦截器FirstInterceptor添加注解@Component，将其注册为1个bean

# springmvc配置文件中开启组件扫描，确保拦截器能够被扫描到
<context:component-scan base-package="com.atguigu.mvc"></context:component-scan>

# springmvc配置文件中配置拦截器，如下方式，会拦截指定请求
<mvc:interceptors>
        <mvc:interceptor>
            <!-- 表示拦截所有请求 -->
            <mvc:mapping path="/**"/>
            <!-- 表示放行该请求 -->
            <mvc:exclude-mapping path="/"/>
            <ref bean="firstInterceptor"></ref>
        </mvc:interceptor>
</mvc:interceptors>

# 编写1个控制器，用于测试
@Controller
public class TestController {

    @RequestMapping("/**/testInterceptor")
    public String testInterceptor(){
        return "success";
    }

}

# 编写1个拦截器
@Component
public class FirstInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("FirstInterceptor-->preHandle");
        // 为true表示放行
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("FirstInterceptor-->postHandle");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("FirstInterceptor-->afterCompletion");
    }
}

# 测试
http://localhost:8080/上下文路径/
# 控制台打印没有打印，说明指定的根路径被放行了

# 测试
http://localhost:8080/上下文路径/testInterceptor
# 控制台打印
FirstInterceptor-->preHandle
FirstInterceptor-->postHandle
FirstInterceptor-->afterCompletion

# 测试二级目录
http://localhost:8080/上下文路径/test/testInterceptor
# 控制台打印
FirstInterceptor-->preHandle
FirstInterceptor-->postHandle
FirstInterceptor-->afterCompletion

• 多个拦截器的执行顺序

# 在拦截器上添加注解@Component，将其注册为bean

# springmvc配置文件中开启组件扫描，确保拦截器能够被扫描到
<context:component-scan base-package="com.atguigu.mvc"></context:component-scan>

# springmvc配置文件中配置拦截器，如下方式，会拦截指定请求
<mvc:interceptors>
    <ref bean="firstInterceptor"></ref>
    <ref bean="secondInterceptor"></ref>
</mvc:interceptors>

# 编写1个控制器，用于测试
@Controller
public class TestController {

    @RequestMapping("/**/testInterceptor")
    public String testInterceptor(){
        return "success";
    }

}

# 编写1个拦截器
@Component
public class FirstInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("FirstInterceptor-->preHandle");
        // 为true表示放行
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("FirstInterceptor-->postHandle");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("FirstInterceptor-->afterCompletion");
    }
}

# 编写第2个拦截器
@Component
public class SecondInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("SecondInterceptor-->preHandle");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("SecondInterceptor-->postHandle");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("SecondInterceptor-->afterCompletion");
    }
}

# 测试1：将2个拦截器改为true
http://localhost:8080/上下文路径/testInterceptor
# 控制台打印
FirstInterceptor-->preHandle
SecondInterceptor-->preHandle
SecondInterceptor-->postHandle
FirstInterceptor-->postHandle
SecondInterceptor-->afterCompletion
FirstInterceptor-->afterCompletion

# 测试2：将2个拦截器改为false
13:43:49.883 [http-nio-8081-exec-1] DEBUG org.springframework.web.servlet.DispatcherServlet - GET "/mvc/", parameters={}
13:43:49.890 [http-nio-8081-exec-1] DEBUG org.springframework.web.servlet.handler.SimpleUrlHandlerMapping - Mapped to ParameterizableViewController [view="index"]
FirstInterceptor-->preHandle
13:43:49.893 [http-nio-8081-exec-1] DEBUG org.springframework.web.servlet.DispatcherServlet - Completed 200 OK
13:43:50.150 [http-nio-8081-exec-3] DEBUG org.springframework.web.servlet.DispatcherServlet - GET "/mvc/", parameters={}
13:43:50.150 [http-nio-8081-exec-3] DEBUG org.springframework.web.servlet.handler.SimpleUrlHandlerMapping - Mapped to ParameterizableViewController [view="index"]
FirstInterceptor-->preHandle

# 结论：
a>若每个拦截器的preHandle()都返回true
此时多个拦截器的执行顺序和拦截器在SpringMVC的配置文件的配置顺序有关：
preHandle()会按照配置的顺序执行，而postHandle()和afterComplation()会按照配置的反序执行
b>若某个拦截器的preHandle()返回了false
preHandle()返回false和它之前的拦截器的preHandle()都会执行，postHandle()都不执行，返回false的拦截器之前的拦截器的afterComplation()会执行

• 查看源码

# 打开DispatcherServlet.java 1061行

# 首先进入如下代码，该执行链中放的是3个拦截器（1个是springmvc自己创建的，2个是我们自己创建的），执行链包括2个部分（控制器方法、处理控制器方法的拦截器）
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
    return;
}

# 当以上的方法，返回false时执行

# 进入applyPreHandle方法，遍历执行链中的拦截器，所以preHandle方法是按顺序执行
	boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
		for (int i = 0; i < this.interceptorList.size(); i++) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
			if (!interceptor.preHandle(request, response, this.handler)) {
				triggerAfterCompletion(request, response, null);
				return false;
			}
			this.interceptorIndex = i;
		}
		return true;
	}

# 之后执行postHandle方法
applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);

# 进入postHandle方法，所以postHandle是反序执行
	void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
			throws Exception {

		for (int i = this.interceptorList.size() - 1; i >= 0; i--) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
			interceptor.postHandle(request, response, this.handler, mv);
		}
	}

# 最后执行afterComplation方法
		finally {
			if (asyncManager.isConcurrentHandlingStarted()) {
				// Instead of postHandle and afterCompletion
				if (mappedHandler != null) {
					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
				}
			}
			else {
				// Clean up any resources used by a multipart request.
				if (multipartRequestParsed) {
					cleanupMultipart(processedRequest);
				}
			}
		}

# 进入applyAfterConcurrentHandlingStarted，所以afterComplation是反序执行的
	void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
		for (int i = this.interceptorList.size() - 1; i >= 0; i--) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
			if (interceptor instanceof AsyncHandlerInterceptor) {
				try {
					AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor) interceptor;
					asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
				}
				catch (Throwable ex) {
					if (logger.isErrorEnabled()) {
						logger.error("Interceptor [" + interceptor + "] failed in afterConcurrentHandlingStarted", ex);
					}
				}
			}
		}
	}