无法使用struts2注释_带有注释且没有struts.xml文件的Struts 2 Hello World示例

无法使用struts2注释

This is the second article in the series of Struts 2 Tutorials. If you have directly come here, I would recommend to check out earlier post too.

这是《 Struts 2教程》系列的第二篇文章。如果您直接来过这里，我也建议您查看之前的帖子。

Struts 2 Beginners Tutorial

Struts 2初学者教程

In last tutorial, we looked into the Struts 2 architecture, it’s components and build a simple Struts 2 web application with XML based configuration (struts.xml). In this tutorial we will see how we can avoid struts configuration file completely using annotations or naming conventions.

在上一教程中，我们研究了Struts 2体系结构及其组件，并使用基于XML的配置（struts.xml）构建了一个简单的Struts 2 Web应用程序。在本教程中，我们将看到如何使用注释或命名约定完全避免struts配置文件。

Struts 2公约概念 (Struts 2 Convention Concept)

Struts 2 uses two methodologies to find out the action classes and result classes. We need to use struts2-convention-plugin API to use any of these methodologies. If you have a normal web application, you can download it’s jar file and put it in the web application lib directory. For maven projects, you can simply add it’s dependency like below.

Struts 2使用两种方法来找出动作类和结果类。我们需要使用struts2-convention-plugin API来使用任何这些方法。如果您有普通的Web应用程序，则可以下载它的jar文件并将其放在Web应用程序的lib目录中。对于Maven项目，您可以像下面这样简单地添加它的依赖项。

<dependency><groupId>org.apache.struts</groupId><artifactId>struts2-convention-plugin</artifactId><version>2.3.15.1</version>
</dependency>

Scanning: In this method, we specify package which needs to be scanned for action classes. The configuration needs to be done in web.xml for Struts 2 filter, like below.
```
<filter><filter-name>struts2</filter-name><filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class><init-param><param-name>actionPackages</param-name><param-value>com.journaldev.struts2.actions</param-value></init-param>
</filter>
```
Struts 2 will find action classes by following methods.
- Any class annotated with @Action or @Actions annotations.
- Any class implementing Action interface or extending ActionSupport class.
- Any class whose name ends with Action and contains execute() method. For these classes, naming convention is used to determine action and results.
扫描：在此方法中，我们指定需要扫描以获取操作类的程序包。需要在web.xml中为Struts 2过滤器完成配置，如下所示。

Struts 2将通过以下方法找到动作类。
- 任何带有@Action或@Actions批注的类。
- 任何实现Action接口或扩展ActionSupport类的类。
- 名称以Action结尾且包含execute（）方法的任何类。对于这些类，使用命名约定来确定操作和结果。
Naming Convention: Struts 2 will automatically create action for classes name ending with Action. The action name is determined by removing the Action suffix and converting first letter to lowercase. So if class name is HomeAction, then action will be “home”.
If these classes are not annotated with @Result to provide the result, then result pages are looked into WEB-INF/content directory and name should be {action}-{return_string}.jsp. So if HomeAction action class is returning “success”, the request will be forwarded to WEB-INF/content/home-success.jsp page.

Using naming convention alone can be very confusing and we can’t use same JSP page for other action classes. So we should try to avoid this and use annotation based configuration.

命名约定 ：Struts 2将自动为以Action结尾的类名称创建action。通过删除动作后缀并将首字母转换为小写来确定动作名称。因此，如果类名称为HomeAction，则操作将为“ home”。

如果未使用@Result注释这些类以提供结果，则将结果页查找到WEB-INF / content目录中，名称应为{action}-{return_string} .jsp。因此，如果HomeAction操作类返回“成功”，则该请求将转发到WEB-INF / content / home-success.jsp页面。

单独使用命名约定可能会造成很大的混乱，我们不能将相同的JSP页面用于其他操作类。因此，我们应该尝试避免这种情况，并使用基于注释的配置。

Now we are ready to create our Hello World struts 2 application using annotations and we won’t have struts 2 configuration file.

现在，我们准备使用批注创建Hello World struts 2应用程序，并且没有struts 2配置文件。

Create a dynamic web project in Eclipse Struts2AnnotationHelloWorld and convert it to maven project. The final project looks like below image.

在Eclipse Struts2AnnotationHelloWorld中创建一个动态Web项目，并将其转换为Maven项目。最终项目如下图所示。

Maven配置 (Maven Configuration)

We have added struts2-core and struts2-convention-plugin dependencies in the pom.xml, final pom.xml code is:

我们在pom.xml中添加了struts2-core和struts2-convention-plugin依赖项，最终的pom.xml代码为：

<project xmlns="https://maven.apache.org/POM/4.0.0" xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="https://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>Struts2AnnotationHelloWorld</groupId><artifactId>Struts2AnnotationHelloWorld</artifactId><version>0.0.1-SNAPSHOT</version><packaging>war</packaging><dependencies><dependency><groupId>org.apache.struts</groupId><artifactId>struts2-core</artifactId><version>2.3.15.1</version></dependency><dependency><groupId>org.apache.struts</groupId><artifactId>struts2-convention-plugin</artifactId><version>2.3.15.1</version></dependency></dependencies><build><plugins><plugin><artifactId>maven-compiler-plugin</artifactId><version>3.1</version><configuration><source>1.6</source><target>1.6</target></configuration></plugin><plugin><artifactId>maven-war-plugin</artifactId><version>2.3</version><configuration><warSourceDirectory>WebContent</warSourceDirectory><failOnMissingWebXml>false</failOnMissingWebXml></configuration></plugin></plugins><finalName>${project.artifactId}</finalName></build>
</project>

部署描述符配置 (Deployment Descriptor Configuration)

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"xmlns="https://java.sun.com/xml/ns/javaee"xsi:schemaLocation="https://java.sun.com/xml/ns/javaee https://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"id="WebApp_ID" version="3.0"><display-name>Struts2AnnotationHelloWorld</display-name><filter><filter-name>struts2</filter-name><filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class><init-param><param-name>actionPackages</param-name><param-value>com.journaldev.struts2.actions</param-value></init-param></filter><filter-mapping><filter-name>struts2</filter-name><url-pattern>/*</url-pattern></filter-mapping></web-app>

Notice the init-param element where we are providing action classes package that will be scanned by struts 2.

请注意init-param元素，我们在其中提供将由struts 2扫描的动作类包。

结果页 (Result Pages)

We have three result pages in our application.

我们的应用程序中有三个结果页面。

login.jsp

<%@ page language="java" contentType="text/html; charset=US-ASCII"pageEncoding="US-ASCII"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "https://www.w3.org/TR/html4/loose.dtd">
<%-- Using Struts2 Tags in JSP --%>
<%@ taglib uri="/struts-tags" prefix="s"%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Login Page</title>
</head>
<body>
<h3>Welcome User, please login below</h3>
<s:form action="login"><s:textfield name="name" label="User Name"></s:textfield><s:textfield name="pwd" label="Password" type="password"></s:textfield><s:submit value="Login"></s:submit>
</s:form>
</body>
</html>

error.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>Error Page</title>
</head>
<body>
<h4>User Name or Password is wrong</h4>
<s:include value="login.jsp"></s:include>
</body>
</html>

welcome.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>Welcome Page</title>
</head>
<body>
<h3>Welcome <s:property value="name"></s:property></h3>
</body>
</html>

Now let’s create our Action classes that we will annotate to configure action and result pages.

现在，让我们创建Action类，我们将对其进行注释以配置操作和结果页面。

带注释的动作类 (Action Classes with Annotations)

package com.journaldev.struts2.actions;import org.apache.struts2.convention.annotation.Action;
import org.apache.struts2.convention.annotation.Actions;
import org.apache.struts2.convention.annotation.Namespace;
import org.apache.struts2.convention.annotation.Namespaces;
import org.apache.struts2.convention.annotation.Result;import com.opensymphony.xwork2.ActionSupport;/*** An empty class for default Action implementation for:* *  <action name="home">*       <result>/login.jsp</result>*    </action>* HomeAction class will be automatically mapped for home.action* Default page is login.jsp which will be served to client* @author pankaj**/@Namespaces(value={@Namespace("/User"),@Namespace("/")})
@Result(location="/login.jsp")
@Actions(value={@Action(""),@Action("home")})
public class HomeAction extends ActionSupport {
}

Notice that HomeAction is an empty class with only purpose to forward the request to login.jsp page.

注意，HomeAction是一个空类，仅用于将请求转发到login.jsp页面。

package com.journaldev.struts2.actions;import org.apache.struts2.convention.annotation.Action;
import org.apache.struts2.convention.annotation.Namespace;
import org.apache.struts2.convention.annotation.Namespaces;
import org.apache.struts2.convention.annotation.Result;/*** Notice the @Action annotation where action and result pages are declared* Also notice that we don't need to implement Action interface or extend ActionSupport* class, only we need is an execute() method with same signature* @author pankaj**/
@Action(value = "login", results = {@Result(name = "SUCCESS", location = "/welcome.jsp"),@Result(name = "ERROR", location = "/error.jsp") })
@Namespaces(value={@Namespace("/User"),@Namespace("/")})
public class LoginAction {public String execute() throws Exception {if("pankaj".equals(getName()) && "admin".equals(getPwd()))return "SUCCESS";else return "ERROR";}//Java Bean to hold the form parametersprivate String name;private String pwd;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPwd() {return pwd;}public void setPwd(String pwd) {this.pwd = pwd;}
}

Notice the use of @Action, @Actions, @Result, @Namespace and @Namespaces annotations, the usage is self explanatory.

注意使用@ Action，@ Actions，@ Result，@ Namespace和@Namespaces批注，其用法不言自明。

Now when we run our application, we get following response pages.

现在，当我们运行应用程序时，我们将获得以下响应页面。

If you have read the last post where we have developed the same application with struts.xml configuration, you will notice that it’s almost same. The only change is the way we wire our application action classes and result pages.

如果您阅读了上一篇文章，其中我们使用struts.xml配置开发了相同的应用程序，那么您会发现它几乎是相同的。唯一的变化是我们连接应用程序操作类和结果页面的方式。

Download Struts2 Annotations Example Project下载Struts2注释示例项目

翻译自: https://www.journaldev.com/2146/struts-2-hello-world-example-with-annotations-and-without-struts-xml-file

无法使用struts2注释