struts2基础——需要注意的几点

struts是流行和成熟的基于MVC设计模式的web应用程序框架，使用struts可以帮助我们减少运用MVC设计模型来开发web应用的时间。目录：一、struts2的工作原理及文件结构二、三种访问Servlet API的方式三、struts接收参数的三种方式四、自定义拦截器

一、struts2的工作原理及文件结构

注：FilterDispatcher被替成StrutsPrepareAndExecuteFilter（如果使用FilterDispatcher过滤器时，程序员自己写的Filter过滤器必须放在所有过滤器的前面。而StrutsPrepareAndExecuteFilter过滤器可以让程序员在执行action之前写自己的Filter）描述Struts流程：网页产生HttpServletRequest请求->经过多个过滤器->到达ActionMaaper，判断是否是action请求（如果是）->通过StrutsPrepareAndExecuteFilter过滤器到达Actionproxy，一方面通过configuration Manager（配置管理器）读取struts.xml文档，另一方面创建一个实例，经过一系列的拦截器->执行到Action->返回result(对应了视图)->经过一系列的拦截器（逆序）->通过HttpServletResponse返回到用户实例。

二、三种访问servlet API的方法

struts2中没有提供任何一个servlet对象，不存在HttpServletRequest，HttpServletResponse对象。但是Struts2提供了三种方式间接的去访问Servlet API

1、ActionContext

通过ActionContext的getContext()静态方法获取ActionContext对象，通过ActionContext对象的一些getSession(),getApplication(),put()等方法，但是千万要注意的是，get获取到的对象都为Map键值对类型。com.opensymphony.xwork2.ActionContext

1 public String execute() {
2         if ("ping".equals(username)) {
3             /*
4              * ActionContext可以获得Servlet对象 但是无法获得response响应对象获得
5              * 获得的request、session、Application 都是Map类型
6              */
7
8             ActionContext.getContext().put("用户名", username);
9             Map session=ActionContext.getContext().getSession();
10             Map application=ActionContext.getContext().getApplication();
11             Map request=(Map)ActionContext.getContext().get(StrutsStatics.HTTP_REQUEST);
12         } else {
13             ActionContext.getContext().put("info", "信息");
14         }
15         return SUCCESS;
16     }

2、ServletActionContext

通过调用ServletActionContext类的一些包括getResponse(),getRequest(),getServletContext()等在内的静态方法，这些静态方法的返回类型是和Servlet中的对象类型是一一对应的。其中getResponse()返回类型为HttpServletResponse，getRequest()返回类型为HttpServletRequest().

1 public String execute2() throws IOException {
2         if ("ping".equals(username)) {
3             HttpServletResponse response=ServletActionContext.getResponse();
4             HttpServletRequest request=ServletActionContext.getRequest();
5             HttpSession session=ServletActionContext.getRequest().getSession();
6             ServletContext application=ServletActionContext.getServletContext();
7         } else {
8
9         }
10         System.out.println(username);
11         return SUCCESS;
12     }

3、实现xxxAware接口

（1）实现ServletRequestAware，ServletResponseAware，ServletSessionAware  

1 public class LoginAction extends ActionSupport implements ServletRequestAware
2
3
4 private HttpServletRequest request;
5 //需实现方法 public void setServletRequest(HttpServletRequest request) { this.request=request; } //response示例
6 public String execute1() throws IOException {
7         if ("ping".equals(username)) {
8             response.setContentType("text/html;charset=utf-8");
9             PrintWriter out = response.getWriter();
10             out.print("<script type='text/javascript'>alert('验证码输入错误!')</script>");
11             out.print("<script type='text/javascript'>location.href='/index.jsp'</script>");
12             out.flush();
13             out.close();
14         } else {
15             response.setContentType("text/html;charset=utf-8");
16             PrintWriter out = response.getWriter();
17             out.print("<script type='text/javascript'>alert('验证码输入错误!')</script>");
18             out.flush();
19             out.close();
20         }
21         System.out.println(username);
22         return SUCCESS;
23     }

（2）实现RequestWare、SessionWare、ApplicationWare等接口

public class LoginAction2 extends ActionSupport implements RequestAware,SessionAware, ApplicationAware {private Map<String, Object> request;private Map<String, Object> session;private Map<String, Object> application;//DI dependency injection//IoC inverse of controlpublic String execute() {request.put("r1", "r1");session.put("s1", "s1");application.put("a1", "a1");return SUCCESS;}@Overridepublic void setRequest(Map<String, Object> request) {this.request = request;}@Overridepublic void setSession(Map<String, Object> session) {this.session = session;}@Overridepublic void setApplication(Map<String, Object> application) {this.application = application;}}

三、struts三种接收参数方式

Struts有三种方式接收参数，且这三种方式都是自动完成赋值的setter方法。

1、使用Action的属性接收参数

代码：struts.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE struts PUBLIC"-//Apache Software Foundation//DTD Struts Configuration 2.3//EN""http://struts.apache.org/dtds/struts-2.3.dtd"><struts><package name="default" namespace="/" extends="struts-default"><action name="LoginAction" method="login" class="com.third.LoginAction1"><result>/loginSuccess.jsp</result></action></package></struts>

login.jsp(登陆提示页面）

<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body><h1>login page</h1><form action="LoginAction.action" method="post"><table><tr><td>username:</td><td><input type="text" name="username"/></td></tr><tr><td>password:</td><td><input type="password" name="password"/></td></tr><tr><td><input type="submit" value="submit"></td><td><input type="reset" value="reset"></td></tr></table></form></body></html>

loginSuccess.jsp（登陆成功提示界面）

<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>login success!</title></head><body><h1>login success!</h1></body></html>

LoginAction.java

 1 package com.third;23 import com.opensymphony.xwork2.ActionSupport;45 public class LoginAction1 extends ActionSupport {67     private String username;8     private String password;910     public String login(){//这里能够打印出来传入的值，则说明能够自动调用setter方法完成赋值11         System.out.println("username:"+username+"  password:"+password);12         return SUCCESS;13     }1415     public String getUsername() {16         return username;17     }1819     public void setUsername(String username) {20         this.username = username;21     }2223     public String getPassword() {24         return password;25     }2627     public void setPassword(String password) {28         this.password = password;29     }3031 }

运行结果截图： 

2、使用DomainModel接收参数

注：这里在表单传值是，必须指明这个属性值，到底穿个action中的那个引用，例如user.username.代码：struts.xml

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd"><struts><package name="default" namespace="/" extends="struts-default"><action name="LoginAction" method="login" class="com.third.LoginAction"><result>/loginSuccess.jsp</result></action></package></struts>  

login.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><base href="<%=basePath%>"><title>My JSP 'login.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">--></head><body><h1>login page!</h1><form action="LoginAction.action" method="post"><table><tr><td>username:</td><td><input type="text" name="user.username"/></td></tr><tr><td>password:</td><td><input type="password" name="user.password"/></td></tr><tr><td><input type="submit" value="submit"></td><td><input type="reset" value="reset"></td></tr></table></form></body></html>

loginSuccess.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><base href="<%=basePath%>"><title>My JSP 'loginSuccess.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">--></head><body><h1>login success!</h1></body></html>

User.java

package com.third;public class User {private String username;private String password;public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}}

LoginAction.java

 1 package com.third;23 import org.apache.struts2.ServletActionContext;45 import com.opensymphony.xwork2.ActionContext;6 import com.opensymphony.xwork2.ActionSupport;7 import com.opensymphony.xwork2.inject.Context;89 public class LoginAction extends ActionSupport {1011     private User user;12     public User getUser() {13         return user;14     }1516     public void setUser(User user) {17         this.user = user;18     }19     public String login(){//这里可以打印出传入的值的话，Action完成了自动调用setter方法赋值20         System.out.println("username:"+user.getUsername()+" password:"+this.getUser().getPassword());21         return SUCCESS;22     }2324 }

运行结果截图：

3、使用ModelDriven接受参数

struts.xml

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd"><struts><package name="default" namespace="/" extends="struts-default"><action name="LoginAction" method="login" class="com.third.LoginAction"><result>/loginSuccess.jsp</result></action></package></struts>    

login.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><base href="<%=basePath%>"><title>My JSP 'login.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">--></head><body><h1>login page!</h1><form action="LoginAction.action" method="post"><table><tr><td>username:</td><td><input type="text" name="username"/></td></tr><tr><td>password:</td><td><input type="password" name="password"/></td></tr><tr><td><input type="submit" value="submit"></td><td><input type="reset" value="reset"></td></tr></table></form></body></html>

loginSuccess.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><base href="<%=basePath%>"><title>My JSP 'loginSuccess.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">--></head><body><h1>login success!</h1></body></html>

User.java

package com.third;public class User {private String username;private String password;public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}}

LoginAction.java

package com.third;import org.apache.struts2.ServletActionContext;import com.opensymphony.xwork2.ActionContext;import com.opensymphony.xwork2.ActionSupport;import com.opensymphony.xwork2.ModelDriven;import com.opensymphony.xwork2.inject.Context;public class LoginAction extends ActionSupport implements ModelDriven<User> {private User user=new User();public String login(){//这里打印出传入的参数值，说明自动调用setter方法赋值System.out.println("username:"+user.getUsername()+" password:"+user.getPassword());return SUCCESS;}@Overridepublic User getModel() {return user;}}

运行结果截图： 

四、自定义拦截器

注：特别要注意在使用拦截的器的时候，使用表单传值，会导致Action中获得的属性的值为null，或是其他的默认的初始化值。1、实现Interceptor接口-void init()方法：初始化拦截器所需要的资源-void destory()方法：释放init()中分配的资源-String intercept(ActionInvocation invocation)throws Exception:实现拦截器功能，利用ActionInvocation参数获取Action状态，返回result字符串作为逻辑视图。代码：struts.xml

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd"><struts><package name="default" namespace="/" extends="struts-default"><!--注册拦截器  --><interceptors><interceptor name="timefigureFilter" class="com.third.TimeInterceptor"></interceptor></interceptors><action name="LoginAction" method="login" class="com.third.LoginAction"><result>/loginSuccess.jsp</result><interceptor-ref name="timefigureFilter"></interceptor-ref></action></package></struts>    

login.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><base href="<%=basePath%>"><title>My JSP 'login.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">--></head><body><h1>login page!</h1><form action="LoginAction.action" method="post"><table><tr><td>username:</td><td><input type="text" name="username"/></td></tr><tr><td>password:</td><td><input type="password" name="password"/></td></tr><tr><td><input type="submit" value="submit"></td><td><input type="reset" value="reset"></td></tr></table></form></body></html>

loginSuccess.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><base href="<%=basePath%>"><title>My JSP 'loginSuccess.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">--></head><body><h1>login success!</h1></body></html>

User.java

package com.third;public class User {private String username;private String password;public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}}

TimeInterceptor.java

 1 package com.third;23 import javax.servlet.http.HttpServletRequest;45 import org.apache.struts2.ServletActionContext;67 import com.opensymphony.xwork2.ActionInvocation;8 import com.opensymphony.xwork2.interceptor.Interceptor;910 public class TimeInterceptor implements Interceptor {1112     @Override13     public void destroy() {14         // TODO Auto-generated method stub1516     }1718     @Override19     public void init() {20         // TODO Auto-generated method stub2122     }2324     @Override25     public String intercept(ActionInvocation invocation) throws Exception {26         HttpServletRequest request=ServletActionContext.getRequest();27         String username=request.getParameter("username");28         String password=request.getParameter("password");29         request.setAttribute("username", username);30         //1执行action之前31         long start=System.currentTimeMillis();32         //2执行下一个拦截器，直到最后一个拦截器，则执行目标Action33         String result=invocation.invoke();34         //3执行完action之后35         long end=System.currentTimeMillis();36         System.out.println("执行Action花费的时间为："+(end-start)+"ms");37         return result;38     }3940 }

  LoginAction.java

 1 package com.third;23 import org.apache.struts2.ServletActionContext;45 import com.opensymphony.xwork2.ActionContext;6 import com.opensymphony.xwork2.ActionSupport;7 import com.opensymphony.xwork2.ModelDriven;8 import com.opensymphony.xwork2.inject.Context;910 public class LoginAction extends ActionSupport implements ModelDriven<User> {1112     private User user=new User();13     public String login(){//着重看着两行代码运行打印的结果14         System.out.println("username:"+user.getUsername());//System.out.println("username:"+ServletContext.getRequest().getAttribute("username");//这里也可完成正常的获值15         System.out.println("username:"+ServletActionContext.getRequest().getAttribute("username"));16         return SUCCESS;17     }1819     @Override20     public User getModel() {2122         return user;23     }2425 }

运行结果截图：注：注意看结果，打印的第一个username的属性值为null，而第二个为表单填写的dasd。这里涉及到拦截器的使用导致的表单传值问题。

分析：拦截器的使用导致的表单传值问题

原因：登陆界面填写完成之后，表单需要实现页面跳转，而这些将会交给struts，struts在调用action的过程其实是调用action中的struts.xml配置action标签method属性指定的方法（默认是execute()）,而在调用这个方法前会对表单的属性信息将会别匹配赋值给action中同名属性。正常情况下没有自定义的拦截器，通过表单传递的属性值没有问题。要完成这个功能，有很大程度上， Struts 2 要依赖与 ValueStack 对象。这个对象贯穿整个 Action 的生命周期 (每个 Action 类的对象实例会拥有一个 ValueStack 对象 ) 。当 Struts 2 接收到一个 action 的请求后，会先建立Action 类的对象实例，但不会调用 Action 方法，而是先将 Action 类的相应属性放到 ValueStack 对象的顶层节点(ValueStack 对象相当于一个栈 ). 只是所有的属性值都是默认的值，如 String 类型的属性值为 null,int 类型的属性值为 0 等。   在处理完上述工作后， Struts 2 就会调用拦截器链中的拦截器，当调用完所有的拦截器后，最后会调用 Action 类的 Action 方法，在调用 Action 方法之前，会将 ValueStack 对象顶层节点中的属性值赋给 Action 类中相应的属性。大家要注意，在这里就给我们带来了很大的灵活性。也就是说，在 Struts 2 调用拦截器的过程中，可以改变ValueStack 对象中属性的值，当改变某个属性值后， Action 类的相应属性值就会变成在拦截器中最后改变该属性的这个值。好多废话~总结就是：在拥有自定义的过滤器时，表单传属性值会先赋值给Action中属性，当运行完过滤器时，才会调用Action中的方法，在调用之前会将 ValueStack 对象中的默认初始化值赋给action中的属性，然后调用action中的方法，这样action中的属性全是ValueStack 对象中的默认初始化值。解决的方法：间接访问Servlet的API，通过request对象去访问属性和属性值。如：HttpServletRequest request=ServletActionContext.getRequest();String username=request.getParameter("username");

2、方式二：继承AbstractInterceptor类

-提供了init()和destroy()方法的实现-只需要实现intercept()方法即可代码：struts.xml

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd"><struts><package name="default" namespace="/" extends="struts-default"><!--注册拦截器  --><interceptors><interceptor name="timefigureFilter1" class="com.third1.TimeInterceptor"></interceptor></interceptors><action name="TimeAction" class="com.third1.TimeAction"><result>/index.jsp</result><!--引用拦截器  --><interceptor-ref name="timefigureFilter1"></interceptor-ref></action></package></struts>    

TimeInterceptor.java

 1 package com.third1;23 import org.apache.struts2.ServletActionContext;45 import com.opensymphony.xwork2.ActionInvocation;6 import com.opensymphony.xwork2.interceptor.AbstractInterceptor;78 public class TimeInterceptor extends AbstractInterceptor {910     @Override11     public String intercept(ActionInvocation invocation) throws Exception {12         //1.执行action之前13         long start=System.currentTimeMillis();14         //2.执行下一个拦截器，如果已经是最后一个拦截器，则执行目标Action1516         ServletActionContext.getRequest().setAttribute("username", "小帅哥");17         ServletActionContext.getRequest().getSession().setAttribute("username","小美女");18         ServletActionContext.getServletContext().setAttribute("username", "少艾");19         String result=invocation.invoke();20         //3.执行Action之后21         long end=System.currentTimeMillis();22         System.out.println("执行Action花费的时间："+(end-start)+"ms");23         //获取request对象，调用其setAttribute函数，将时间作为属性保存到request对象中24         ServletActionContext.getRequest().setAttribute("time", (end-start));25         ServletActionContext.getRequest().getSession().setAttribute("time1",(end-start));26         ServletActionContext.getServletContext().setAttribute("time2", (end-start));27         return result;28     }2930 }

TimeAction.java

 1 package com.third1;23 import com.opensymphony.xwork2.ActionSupport;45 public class TimeAction extends ActionSupport {67     @Override8     public String execute() throws Exception{910         for(int i=0;i<3;i++){11             Thread.sleep(1000);12         }13         return SUCCESS;14     }15 }

index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><base href="<%=basePath%>"><title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">--></head><body><h1>执行Action用户名：<%=request.getAttribute("username") %>（通过request方式获取）</h1><h1>执行Action用户名：<%=session.getAttribute("username") %>（通过session方式获取）</h1><h1>执行Action用户名：<%=application.getAttribute("username") %>（通过application方式获取）</h1><h1>执行Action花费的时间：<%=request.getAttribute("time") %>（通过request方式获取）</h1><h1>执行Action花费的时间：<%=session.getAttribute("time1") %>（通过session方式获取）</h1><h1>执行Action花费的时间：<%=application.getAttribute("time2") %>（通过application方式获取）</h1></body></html>

运行结果截图：分析：对比两种颜色标记的代码区，对比一下他们，并且结合结果进行分析。我们不难发现过滤器的调用分为两个阶段，第一个阶段是在产生HttpServletRequest请求之后、action方法调用之前；第二阶段是产生与action之后，jsp页面（Template显示）跳转之后，HttpServletResponse之前。所以当你在String result=invocation.invoke();   这条语句之后通过request，application，session给它设置属性值，将会没有起到任何作用。可以结合struts2的工作原理及文件结构图进行参考。