Struts 2.0的Action讲解

http://www.35java.com/zhibo/forum.php?mod=viewthread&tid=374&extra=page%3D3
有Struts 1.x经验的朋友都知道Action是Struts的核心内容，当然Struts 2.0也不例外。不过，Struts 1.x与Struts 2.0的Action模型很大的区别。
                                                 Struts 1.x Stuts 2.0
接口 必须继承org.apache.struts.action.Action或者其子类 无须继承任何类型或实现任何接口
表单数据 表单数据封装在FormBean中 表单数据包含在Action中，通过Getter和Setter获取
                                虽然，理论上Struts 2.0的Action无须实现任何接口或继承任何类型，但是，我们为了方便实现Action，大多数情况下都会继承com.opensymphony.xwork2.ActionSupport类，并重载（Override）此类里的String execute()方法。具体的实现，如例1所示：
                                                <%                                @ page contentType                                =                                "                                text/html; charset=UTF-8                                "                               
                                %>                               
                                <%                                @ taglib prefix                                =                                "                                s                                "                                uri                                =                                "                                /struts-tags                                "                               
                                %>                               
                                <                                html                                >                               
                                <                                head                                >                               
                                <                                title                                >                                Hello World!                                </                                title                                >                               
                                </                                head                                >                               
                                <                                body                                >                               
                                <                                h2                                ><                                s:property                                 value                                ="message"                                /></                                h2                                >                               
                                </                                body                                >                               
                                </                                html                                >               
                例1 HelloWorld.jsp               
               
                                                                                package                                tutorial;

                                import                                java.text.DateFormat;
                                import                                java.util.Date;

                                import                                com.opensymphony.xwork2.ActionSupport;

                                public                               
                                class                                HelloWorld                                 extends                                ActionSupport                                                                                                                                                                                                 {
                                                    private                                                String message;
   
                                                    public                                                String getMessage()                                                                                                                                                                                                                                                                                 {
                                                                        return                                                                message;
    }                                                                                                                                                               
                                                                   
    @Override
                                                    public                                                String execute()                                                                                                                                                                                                                                                                                 {
        message                                                                 =                                                               
                                                                "                                                                Hello World, Now is                                                                 "                                                               
                                                                +                                                                DateFormat.getInstance().format(                                                                new                                                                Date());
                                                                        return                                                                SUCCESS;
    }                                                                                                                                                               
                                                                }                                               
                例1 classes/tutorial/HelloWorld.java               
               
                                                <                                package                                 name                                ="ActionDemo"                                extends                                ="struts-default"                                >                               
                                <                                action                                 name                                ="HelloWorld"                                class                                ="tutorial.HelloWorld"                                >                               
                                <                                result                                >                                /HelloWorld.jsp                                </                                result                                >                               
                                </                                action                                >                               
                                </                                package                                >               
                例1 classes/struts.xml中HelloWorld Action的配置               
               
                在浏览器地址栏中键入http://localhost:8080/Struts2_Action/HelloWorld.action，可以看到如图1所示页面。
                               
                图1 HelloWorld输出页面               
               
参考JavaDoc，可知ActionSupport类实现了接口：
com.opensymphony.xwork2.Action
com.opensymphony.xwork2.LoaleProvider
com.opensymphony.xwork2.TextProvider
com.opensymphony.xwork2.Validateable
com.opensymphony.xwork2.ValidationAware
com.uwyn.rife.continuations.ContinuableObject
java.io.Searializable
java.lang.Cloneable

默认情况下，当请求HelloWorld.action发生时，Struts运行时（Runtime）根据struts.xml里的Action映射集(Mapping)，实例化tutoiral.HelloWorld类，并调用其execute方法。当然，我们可以通过以下两种方法改变这种默认调用。这个功能（Feature）有点类似Struts 1.x中的LookupDispathAction。

在classes/sturts.xml中新建Action，并指明其调用的方法；
访问Action时，在Action名后加上“!xxx”（xxx为方法名）。

实现方法请参考例2：
在classes/tutorial/HelloWorld.java中加入以下方法：
public String aliasAction() {
    message =
"自定义Action调用方法";
    return SUCCESS;
}
例2 classes/tutorial/HelloWorld.java代码片段

实现方法一，在classes/sturts.xml中加入下面代码：
<action name="AliasHelloWorld" class="tutorial.HelloWorld" method="aliasAction">
<result>/HelloWorld.jsp</result>
</action>
例2 classes/struts.xml中AlaisHelloWorld Action的配置

实现方法二，使用http://localhost:8080/Struts2_Action/HelloWorld!aliasAction.action地址来访问HelloWorld Action。 在浏览器地址栏中键入http://localhost:8080/Struts2_Action/AliasHelloWorld.action或 http://localhost:8080/Struts2_Action/HelloWorld!aliasAction.action，可以看到如图2所示页面。

图2 自定义Action调用方法页面通过上面的两个例子，细心的朋友应该可能会发现classes/tutorial/HelloWorld.java中Action方法（execute和aliasAction）返回都是SUCCESS。这个属性变量我并没有定义，所以大家应该会猜到它在ActionSupport或其父类中定义。没错，SUCCESS在接口com.opensymphony.xwork2.Action中定义，另外同时定义的还有ERROR, INPUT, LOGIN, NONE。
此外，我在配置Action时都没有为result定义名字（name），所以它们默认都为success。值得一提的是Struts 2.0中的result不仅仅是Struts 1.x中forward的别名，它可以实现除forward外的很激动人心的功能，如将Action输出到FreeMaker模板、Velocity模板、JasperReports和使用XSL转换等。这些都过result里的type（类型）属性（Attribute）定义的。另外，您还可以自定义result类型。
下面让我们来做一个Velocity模板输出的例子，首先在classes/struts.xml中新建一个Action映射（Mapping），将其result类型设为velocity，如以下代码所示：
<action name="VMHelloWorld" class="tutorial.HelloWorld">
<result type="velocity">/HelloWorld.vm</result>
</action>
例3 classes/struts.xml中VMHelloWorld Action的配置

新建HelloWorld.vm，内容如下所示：
<html>
<head>
<title>Velocity</title>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
</head>
<body>
<h2>Message rendered in Velocity: $message</h2>
</body>
</html>
例3 HelloWorld.vm
在浏览器地址栏中键入http://localhost:8080/Struts2_Action/VMHelloWorld.action，页面输出如下图3所示。

图3 HelloWorld.vm的输出页面 要运行例3需要在WEB-INF/lib中添加以下几个包：
commons-collections-3.2.jar
velocity-1.4.jar
velocity-tools-view-1.2.jar
avalon-logkit-2.1.jar


前面，我花了不少的时间讨论Action的输出。我老板有句名言——程序无非就是输入、操作和输出。因此，现在我们要讨论一下输入——表单输入。
使用Struts 2.0，表单数据的输入将变得非常方便，和普通的POJO一样在Action编写Getter和Setter，然后在JSP的UI标志的name与其对应，在提交表单到Action时，我们就可以取得其值。
让我们看一个例子，新建Login Action，它通过Login.jsp的表单获得用户名和密码，验查用户名是否为“max”，密码是否则为“secret”。如果，两者都符合，就在HelloWorld中显示“Welcome, max”，否则显示“Invalid user or Password”。
package tutorial;

import com.opensymphony.xwork2.ActionSupport;

public
class Login extends ActionSupport {
    private String name;
    private String password;
    private String message;
   
    public String getName() {
        return name;
    }
   
    public
void setName(String name) {
        this.name = name;
    }
   
    public String getPassword() {
        return password;
    }
   
    public
void setPassword(String password) {
        this.password = password;
    }
   
    public String getMessage() {
        return message;
    }

    @Override
    public String execute() {
        if("max".equals(name) &&
"Secret".equals(password)) {
            message =
"Welcome, "
+ name;
        }
else
{
            message =
"Invalid user or password";
        }
        return SUCCESS;
    }
}
例4 classes/tutorial/Login.java

<%@ page contentType="text/html; charset=UTF-8"
%>
<%@ taglib prefix="s" uri="/struts-tags"
%>
<html>
<head>
<title>Login</title>
</head>
<body>
<s:form action="Login" method="POST">
<s:textfield name="name" label="User name"
/>
<s:password name="password" label="Password"
/>
<s:submit value="Submit"/>
</s:form>
</body>
</html>
例4 Login.jsp

<action name="Login" class="tutorial.Login">
<result>/HelloWorld.jsp</result>
</action>
例4 classes/struts.xml中Login Action的配置

运行Tomcat，在浏览器地址栏中键入http://localhost:8080/Struts2_Action/Login.jsp，出现如图4所示页面。


图4 Login.jsp输出页面

分别在User name中输入“max”和“secret”，点击“Submit”按钮，出现如图5所示页面。



图5 Login成功页面

在浏览器地址栏中键入http://localhost:8080/Struts2_Action/Login.jsp，分别在User name中输入“Scott”和“password”，点击“Submit”按钮，出现如图6所示页面。


图6 Login失败页面  Struts 2.0更厉害的是支持更高级的POJO访问，如user.getPassword()。我们可以用另一写法实现例4。首先，将name和password从Login类中分离出来，到新建类User中。这样对我们开发多层系统尤其有用。它可以使系统结构更清晰。
package tutorial;

import com.opensymphony.xwork2.ActionSupport;

public
class LoginX extends ActionSupport {
    private User user;
    private String message;
   
    public
void setUser(User user) {
        this.user = user;
    }
   
    public User getUser() {
        return user;
    }
   
    public String getMessage() {
        return message;
    }
   
    @Override
    public String execute() {       
        if("max".equals(user.getName()) &&
"secret".equals(user.getPassword())) {
            message =
"Welcome, "
+ user.getName();
        }
else
{
            message =
"Invalid user or password";
        }
        return SUCCESS;
    }
}
例5 classes/tutorial/LoginX.java

<%@ page contentType="text/html; charset=UTF-8"
%>
<%@ taglib prefix="s" uri="/struts-tags"
%>
<html>
<head>
<title>Login</title>
</head>
<body>
<s:form action="LoginX" method="POST">
<s:textfield name="user.name" label="User name"
/>
<s:password name="user.password" label="Password"
/>
<s:submit value="Submit"/>
</s:form>
</body>
</html>
例5 LoginX.jsp

<action name="LoginX" class="tutorial.LoginX">
<result>/HelloWorld.jsp</result>
</action>
例5 classes/struts.xml中的LoginX Action配置  很多时候我的同事会问我：“如果我要取得Servlet API中的一些对象，如request、response或session等，应该怎么做？这里的execute不像Struts 1.x的那样在参数中引入。”开发Web应用程序当然免不了跟这些对象打交道。在Strutx 2.0你可以有两种方式获得这些对象：非IoC（控制反转Inversion of Control）方式和IoC方式。

非IoC方式
要获得上述对象，关键Struts 2.0中com.opensymphony.xwork2.ActionContext类。我们可以通过它的静态方法getContext()获取当前Action的上下文对象。 另外，org.apache.struts2.ServletActionContext作为辅助类（Helper Class），可以帮助您快捷地获得这几个对象。


HttpServletRequest request = ServletActionContext.getRequest();
HttpServletResponse response = ServletActionContext.getResponse();
HttpSession session = request.getSession();

如果你只是想访问session的属性（Attribute），你也可以通过ActionContext.getContext().getSession()获取或添加session范围（Scoped）的对象。
IoC方式
要使用IoC方式，我们首先要告诉IoC容器（Container）想取得某个对象的意愿，通过实现相应的接口做到这点。具体实现，请参考例6 IocServlet.java。

package tutorial;

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

import org.apache.struts2.ServletActionContext;

import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionSupport;

public
class NonIoCServlet extends ActionSupport {
    private String message;
   
    public String getMessage() {
        return message;       
    }
   
    @Override
    public String execute() {   
        ActionContext.getContext().getSession().put("msg", "Hello World from Session!");
       
        HttpServletRequest request = ServletActionContext.getRequest();
        HttpServletResponse response = ServletActionContext.getResponse();       
        HttpSession session = request.getSession();
       
        StringBuffer sb =
new StringBuffer("Message from request: ");
        sb.append(request.getParameter("msg"));
        sb.append("<br>Response Buffer Size: ");
        sb.append(response.getBufferSize());
        sb.append("<br>Session ID: ");
        sb.append(session.getId());
       
        message = sb.toString();
        return SUCCESS;
    }
}
例6 classes/tutorial/NonIoCServlet.java

package tutorial;

import java.util.Map;

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

import org.apache.struts2.interceptor.ServletRequestAware;
import org.apache.struts2.interceptor.ServletResponseAware;
import org.apache.struts2.interceptor.SessionAware;

import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionSupport;

public
class IoCServlet extends ActionSupport implements SessionAware, ServletRequestAware, ServletResponseAware {
    private String message;
    private Map att;
    private HttpServletRequest request;
    private HttpServletResponse response;   
   
    public String getMessage() {
        return message;       
    }
   
    public
void setSession(Map att) {
        this.att = att;
    }
   
    public
void setServletRequest(HttpServletRequest request) {
        this.request = request;
    }
   
    public
void setServletResponse(HttpServletResponse response) {
        this.response = response;
    }
   
    @Override
    public String execute() {       
        att.put("msg", "Hello World from Session!");
       
        HttpSession session = request.getSession();
       
        StringBuffer sb =
new StringBuffer("Message from request: ");
        sb.append(request.getParameter("msg"));
        sb.append("<br>Response Buffer Size: ");
        sb.append(response.getBufferSize());
        sb.append("<br>Session ID: ");
        sb.append(session.getId());
       
        message = sb.toString();
        return SUCCESS;
    }
}
例6 classes/tutorial/IoCServlet.java

<%@ page contentType="text/html; charset=UTF-8"
%>
<%@ taglib prefix="s" uri="/struts-tags"
%>
<html>
<head>
<title>Hello World!</title>
</head>
<body>
<h2>
<s:property value="message" escape="false"/>
<br>Message from session: <s:property value="#session.msg"
/>
</h2>
</body>
</html>
例6 Servlet.jsp

<action name="NonIoCServlet" class="tutorial.NonIoCServlet">
<result>/Servlet.jsp</result>
</action>
<action name="IoCServlet" class="tutorial.IoCServlet">
<result>/Servlet.jsp</result>
</action>
例6 classes/struts.xml中NonIocServlet和IoCServlet Action的配置运行Tomcat，在浏览器地址栏中键入http://localhost:8080/Struts2_Action/NonIoCServlet.action?msg=Hello%20World! 或http://localhost:8080/Struts2_Action/IoCServlet.action?msg=Hello%20World!，出现如图7所示页面。


图7 Servlet.jsp的输出页面