struts2 拦截器

Sometimes we have long running actions where user will have to wait for final result. In this case, user can get annoyed with no response and may refresh the page causing issues in application.

有时，我们需要长时间运行，因此用户必须等待最终结果。 在这种情况下，用户可能会无响应而烦恼，并且可能会刷新导致应用程序出现问题的页面。

Struts2 provide execAndWait interceptor that we can use for long running action classes to return an intermediate result to user while the processing is happening at server side. Once the processing is finished, user will be presented with the final result page.

Struts2提供了execAndWait拦截器，我们可以将其用于长时间运行的动作类，以便在服务器端进行处理时向用户返回中间结果。 处理完成后，将向用户显示最终结果页面。

Struts2 execAndWait interceptor is already defined in the struts-default package and we just need to configure it for our action classes. The implementation is present in ExecuteAndWaitInterceptor class that returns “wait” result page until the processing of action class is finished.

在struts-default包中已经定义了Struts2 execAndWait拦截器，我们只需要为我们的操作类配置它即可。 该实现存在于ExecuteAndWaitInterceptor类中，该类返回“ wait ”结果页面，直到操作类的处理完成。

The interceptor provides two variables – delay to return the wait response for first time and delaySleepInterval to check if the action class processing is finished. Both of these variables can be overridden in struts configuration and measured in milliseconds.

拦截器提供了两个变量- 延迟第一次返回等待响应和延迟SleepInterval以检查动作类处理是否完成。 这两个变量都可以在struts配置中被覆盖，并以毫秒为单位进行测量。

We will look into this with a simple web application project whose project structure looks like below image. Create the dynamic web project in Eclipse with name as Struts2ExecAndWait and configure it as maven project.

我们将通过一个简单的Web应用程序项目对此进行研究，其项目结构如下图所示。 在Eclipse中创建名为Struts2ExecAndWait的动态Web项目，并将其配置为maven项目。

项目配置 (Project Configuration)

Add below filter in web.xml to configure web application to use Struts2 framework.

在web.xml中添加以下过滤器，以配置Web应用程序以使用Struts2框架。

<filter><filter-name>struts2</filter-name><filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class></filter><filter-mapping><filter-name>struts2</filter-name><url-pattern>/*</url-pattern></filter-mapping>

Add struts2-core dependency in pom.xml file like below.

在pom.xml文件中添加struts2-core依赖项，如下所示。

<dependencies><dependency><groupId>org.apache.struts</groupId><artifactId>struts2-core</artifactId><version>2.3.15.1</version></dependency></dependencies>

struts.xml配置 (struts.xml configuration)

struts.xml

struts.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE struts PUBLIC"-//Apache Software Foundation//DTD Struts Configuration 2.3//EN""https://struts.apache.org/dtds/struts-2.3.dtd">
<struts><!-- constant to define result path locations to project root directory --><constant name="struts.convention.result.path" value="/"></constant><package name="user" namespace="/" extends="struts-default"><action name="run"><result>/run.jsp</result></action><action name="ExecuteTask" class="com.journaldev.struts2.actions.ExecuteTaskAction"><interceptor-ref name="defaultStack"></interceptor-ref><interceptor-ref name="execAndWait"><!-- override delay and delaySleepInterval parameters of execAndWait to 500ms --><param name="delay">500</param><param name="delaySleepInterval">500</param></interceptor-ref><result name="wait">/running.jsp</result><result name="success">/success.jsp</result></action></package></struts>

The entry point of application is run.action through which user will provide time to execute the task in seconds. The task will be executed by ExecuteTaskAction. We have overridden the interceptors for ExecuteTask action to have defaultStack first and then execAndWait interceptor.

应用程序的入口点是run.action，通过它用户将以秒为单位提供执行任务的时间。 该任务将由ExecuteTaskAction执行。 我们已经重写了ExecuteTask操作的拦截器，使其首先具有defaultStack，然后具有execAndWait拦截器。

Note that execAndWait interceptor should be the last one in the interceptors stack. We are also overriding delay and delaySleepInterval values to 500ms. Default value for delay is 0 and delaySleepInterval is 100ms.

注意execAndWait拦截器应该是拦截器堆栈中的最后一个。 我们也将delay和delaySleepInterval值重写为500ms。 延迟的默认值为0，delaySleepInterval为100ms。

ExecuteAndWaitInterceptor returns wait result as intermediate response, so we need to configure this as result page for the action. Once the processing is finished success result is returned to the user.

ExecuteAndWaitInterceptor返回等待结果作为中间响应，因此我们需要将其配置为操作的结果页面。 处理完成后，成功结果将返回给用户。

动作班 (Action Class)

package com.journaldev.struts2.actions;import java.util.Date;import com.opensymphony.xwork2.ActionSupport;public class ExecuteTaskAction extends ActionSupport {@Overridepublic String execute() {//process task for given timeSystem.out.println("Starting execution. Current time: "+new Date());processTask();System.out.println("Ending execution. Current time: "+new Date());return SUCCESS;}private void processTask() {System.out.println("Time to process:"+processingTime);try {Thread.sleep(getProcessingTime()*1000);} catch (InterruptedException e) {e.printStackTrace();}}private int processingTime;public int getProcessingTime() {return processingTime;}public void setProcessingTime(int processingTime) {this.processingTime = processingTime;}}

Action class is very simple and just waits for input time to return the success response. In real life, there might be heavy processing involved causing the delay in response.

动作类非常简单，只需等待输入时间即可返回成功响应。 在现实生活中，可能涉及大量处理，导致响应延迟。

JSP页面 (JSP Pages)

run.jsp

run.jsp

<%@ page language="java" contentType="text/html; charset=US-ASCII"pageEncoding="US-ASCII"%>
<%@ taglib uri="/struts-tags" prefix="s" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "https://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Long Process Input Page</title>
</head>
<body>
<h3>ExecAndWait Interceptor Example</h3>
<s:form action="ExecuteTask">
<s:textfield name="processingTime" label="Enter seconds to execute task"></s:textfield>
<s:token />
<s:submit name="submit" label="Run" align="center"></s:submit>
</s:form>
</body>
</html>

This is the entry point of the application and use in run action. We are required to have token in the form so that execAndWait interceptor can identify the request.

这是应用程序的入口，并在运行操作中使用。 我们需要具有以下形式的令牌，以便execAndWait拦截器可以标识请求。

running.jsp

running.jsp

<%@ page language="java" contentType="text/html; charset=US-ASCII"pageEncoding="US-ASCII"%>
<%@ taglib uri="/struts-tags" prefix="s" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "https://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<meta http-equiv="refresh" content="2;url=<s:url includeParams="all" />"/>
<%--
<meta http-equiv="refresh" content="2"/>"/>
Above refresh meta will also work as long as browser supports cookie,
by including params above we are making sure that it will work even when cookies are disabled--%>
<title>Processing intermediate page</title>
</head>
<body>
<h3>Your request is getting processed</h3>
<img alt="processing" src="data:images/processing.gif" align="middle">
</body>
</html>

This is the intermediate response returned by the execAndWait interceptor. This page should have “refresh” meta where request will be sent to server to get the final response. If we won’t have this, then browser will not send the further requests and stuck on this page. We are refreshing the page every 2 seconds and passing all the input parameters to server. We are also showing processing.gif in the page to look like some processing is happening.

这是execAndWait拦截器返回的中间响应。 该页面应具有“ refresh ”元，将请求发送到服务器以获取最终响应。 如果我们没有这个选项，那么浏览器将不会发送进一步的请求并停留在此页面上。 我们每2秒刷新一次页面，并将所有输入参数传递给服务器。 我们还在页面中显示processing.gif，看起来正在处理中。

success.jsp

success.jsp

<%@ page language="java" contentType="text/html; charset=US-ASCII"pageEncoding="US-ASCII"%>
<%@ taglib uri="/struts-tags" prefix="s" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "https://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Long Process Success Page</title>
</head>
<body>
<h3>Task executed for <s:property value="processingTime"/> seconds successfully.</h3>
</body>
</html>

A simple response page that is the final result returned by the action class.

一个简单的响应页面，是操作类返回的最终结果。

When we run the application, we get following response pages.

当我们运行应用程序时，我们得到以下响应页面。

That’s all for execAndWait interceptor example, token is also used in Struts2 token interceptor to handle double form submission.

这就是execAndWait拦截器示例的全部内容，在Struts2令牌拦截器中还使用了令牌来处理双重表单提交 。

Read more about interceptors at Struts2 interceptors tutorial.

在Struts2拦截器教程中阅读有关拦截器的更多信息。

翻译自: https://www.journaldev.com/2296/struts2-execandwait-interceptor-example-for-long-running-actions

struts2 拦截器