java struts2入门学习---拦截器学习

一、拦截器，拦截器栈

1、拦截器的作用

拦截器本质上和servlet的过滤器是一样的。在struts2中，拦截器能够对Action前后进行拦截，拦截器是一个可插拨的，你可以选择使用拦截器，也可以卸载拦截器。

2、拦截器执行顺序

在struts.xml文件中,<intercepto-ref/>中先引用的先执行，后引用的后执行。如果某个拦截器出错或不允许通过，那么下一个拦截器是不允许执行的。

需要拦截哪个Action,就在哪个Action对应的<action>标签中配置即可。

在部署web应用时，拦截器的空参构造方法和init()方法各执行一次，每次请求时intercept()方法都会执行一次。

3、自定义拦截器

1) 声明一个拦截器

<pacakge >

<interceptors>

            <interceptor name="LoginInterceptor" class="interceptor.LoginInterceptor">

            </interceptor>

</interceptors>

<action ></action>

</package>

注意：这里interceptors与action标签同级。其中class对应拦截器的全路径。name对应拦截器的名称，这个可以自己随便定义，建议与类名相同，此名称要唯一。

2)引用一个拦截器：

<action>

<!-- 引用自定义的拦截器 -->

<interceptor-ref name="LoginInterceptor"></interceptor-ref>

<action>

注意：如何引用一个拦截器？即在Action中<action>标签下配置即可。这里name名称与自定义的名称要一致。

4、自定义拦截器栈

1）声明一个拦截器栈

interceptor-stack标签中进行配置需要引用的拦截器，如下:

<interceptors>

            <interceptor name="LoginInterceptor" class="interceptor.LoginInterceptor"></interceptor>

            <interceptor-stack name="amosStack">

                <interceptor-ref name="LoginInterceptor"></interceptor-ref>

                <interceptor-ref name="defaultStack"></interceptor-ref>

            </interceptor-stack>

        </interceptors>

2）引用一个拦截器栈：

<!-- 引用自定义的拦截器栈 -->

<interceptor-ref name="amosStack"></interceptor-ref>

二、需求分析

java struts2入门学习---拦截器学习

如图所示，访问upload.jsp进行上传文件－－》LoginInterceptor拦截器进行拦截－－－》

1、未登录，那么跳转页面到登录页面－－－》进行登录页面－－》登录成功－－－》可以点击返回到上传文件页面；

2、已登录，登录直接开始上传文件。

三、代码分析：

upload.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8"%>

<%@ taglib uri="/struts-tags" prefix="s"  %>

<!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>

    <s:form action="UploadAction" enctype="multipart/form-data" method="POST">

        <s:textfield label="上传用户" name="username"/>

        <s:file label="上传文件" name="upload" />

        <s:file label="上传文件" name="upload" />

        <%-- <s:file label="上传文件" name="upload" /> --%>

        <s:submit value="提交"/>

    </s:form>

</body>

</html>

upload_success.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8"%>

<%@ taglib uri="/struts-tags" prefix="s"  %>

<!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>

    <s:form action="UploadAction" enctype="multipart/form-data" method="POST">

        <s:textfield label="上传用户" name="username"/>

        <s:file label="上传文件" name="upload" />

        <s:file label="上传文件" name="upload" />

        <%-- <s:file label="上传文件" name="upload" /> --%>

        <s:submit value="提交"/>

    </s:form>

</body>

</html>

login.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8"%>

<%@ taglib uri="/struts-tags"  prefix="s"%>

<!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</title>

</head>

<body>

    <s:form action="LoginAction" method="POST">

        <s:textfield label="上传用户" name="username"/>

        <s:submit value="登录"/>

    </s:form>

</body>

</html>

login_success.jsp

<%@ 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>

登录成功<br>

<%-- ${pageContext.request.contextPath } --%>

    <a href="upload.jsp" >返回上传页面</a>

</body>

</html>

sturts.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>

<!--     <include file="config/upload.xml"></include>

 -->

    <!-- 加载其他配置文件 -->

    <include file="config/upload-interceptor.xml"></include>

</struts>

upload-sturts.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="login" extends="struts-default">

        <action name="LoginAction" class="interceptor.LoginAction"

            method="loginMethod">

            <result>

                /login_success.jsp

            </result>

        </action>

    </package>

    <package name="upload" extends="struts-default">

        <interceptors>

            <interceptor name="LoginInterceptor" class="interceptor.LoginInterceptor"></interceptor>

            <interceptor-stack name="amosStack">

                <interceptor-ref name="LoginInterceptor"></interceptor-ref>

                <interceptor-ref name="defaultStack"></interceptor-ref>

            </interceptor-stack>

        </interceptors>

        <action name="UploadAction" class="action.UploadAction" method="uploadMethod">

            <param name="uploadPath">/home/amosli/develop/struts2_learn/</param>

            <result name="success" type="dispatcher">

                /WEB-INF/upload_success.jsp

            </result>

            <result name="input" type="dispatcher">

                upload.jsp

            </result>

            <result name="toLoginJsp" type="dispatcher">

                login.jsp

            </result>

            <!-- 对系统的拦截器进行设置 -->

            <interceptor-ref name="fileUpload">

                <!-- 对单个上传文件的大小进行设置,5M -->

                <param name="maximumSize">5242880</param>

                <!-- 对允许的文件扩展名进行设置,这里以英文逗号隔开 -->

                <param name="allowedExtensions">.txt,.xml</param>

                <!-- 对允许的文件类型进行设置，这里以英文逗号进行隔开 -->

                <param name="allowedTypes">text/plain,text/xml</param>

            </interceptor-ref>

            <!-- 引用自定义的拦截器 -->

            <!-- <interceptor-ref name="LoginInterceptor"></interceptor-ref> -->            <!-- 显示引用默认的拦截器 -->

            <!-- <interceptor-ref name="defaultStack"></interceptor-ref> -->

            <!-- 引用自定义的拦截器栈 -->

            <interceptor-ref name="amosStack"></interceptor-ref>

        </action>

    </package>

</struts>

LoginAction.java

package interceptor;

import java.util.Map;

import com.opensymphony.xwork2.ActionContext;

import com.opensymphony.xwork2.ActionSupport;

/**

 * @ClassName: LoginAction

 * @Description: 用户登录

 * @author: amosli

 * @email:amosli@infomorrow.com

 * @date Jan 17, 2014 12:11:35 AM

 */

public class LoginAction extends ActionSupport {

    private static final long serialVersionUID = 3514444221760688282L;

    private String username;

    public void setUsername(String username) {

        this.username = username;

    }

    public String loginMethod() {

        // 取得HTPPSession

        Map<String, Object> session = ActionContext.getContext().getSession();

        session.put("username", username);

        return SUCCESS;

    }

}

LoginInterceptor.java

package interceptor;

import java.util.Map;

import action.UploadAction;

import com.opensymphony.xwork2.ActionContext;

import com.opensymphony.xwork2.ActionInvocation;

import com.opensymphony.xwork2.interceptor.Interceptor;

/**

 * @ClassName: LoginInterceptor

 * @Description: 登录拦截器

 * @author: amosli

 * @email:amosli@infomorrow.com

 * @date Jan 17, 2014 11:42:54 PM

 */

public class LoginInterceptor implements Interceptor {

    private static final long serialVersionUID = 8314579656513662711L;

    public LoginInterceptor() {

        System.out.println("LoginInterceptor():" + this.hashCode());

    }

    public void destroy() {

        System.out.println("destroy()");

    }

    public void init() {

        System.out.println("init()");

    }

    public String intercept(ActionInvocation invocation) throws Exception {

        System.out.println("LoginInterceptor");

        // //获取此拦截器将要拦截的action

        // Object action = invocation.getAction();

        // System.out.println("action:"+action);//action:action.UploadAction@6522cf92

        // //获取action的返回值

        // String resultValue = invocation.invoke();

        // System.out.println("resultValue:"+resultValue);// resultValue:success

        // 如果拦截器将要拦截的action为UploadAction，那么判断用户是否已经登录

        if (invocation.getAction() instanceof UploadAction) {

            Map<String, Object> session = ActionContext.getContext().getSession();

            if (session.get("username") != null) {// 判断用户是否已经登录

                // 如果返回值为"success"那么将会匹配到配置文件中为result属性为"success"的内容。

                // 如果返回值为invocation.invoke(),那么将会执行uploadaction方法

                return invocation.invoke();

            } else {

                return "toLoginJsp";

            }

        }

        return null;

    }

}

UploadAction.java

package action;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.InputStream;

import java.io.OutputStream;

import com.opensymphony.xwork2.ActionSupport;

/**

 * @ClassName: UploadAction

 * @Description: 文件上传

 * @author: amosli

 * @email:amosli@infomorrow.com

 * @date Jan 14, 2014 1:50:28 AM

 */

public class UploadAction extends ActionSupport {

    private static final long serialVersionUID = -8920466592471253212L;

    private String username;// 用户名

    private String[] uploadContentType;// 上传文件的类型,(Fileupload拦截器传入的参数)

    private File[] upload;// 上传的文件,(Fileupload拦截器传入的参数)

    private String[] uploadFileName;// 上传文件的真实文件名，(Fileupload拦截器传入的参数)

    private String uploadPath;

    public void setUploadPath(String uploadPath) {

        this.uploadPath = uploadPath;

    }

    public void setUsername(String username) {

        this.username = username;

    }

    public String[] getUploadContentType() {

        return uploadContentType;

    }

    public void setUploadContentType(String[] uploadContentType) {

        this.uploadContentType = uploadContentType;

    }

    public File[] getUpload() {

        return upload;

    }

    public void setUpload(File[] upload) {

        this.upload = upload;

    }

    public String[] getUploadFileName() {

        return uploadFileName;

    }

    public void setUploadFileName(String[] uploadFileName) {

        this.uploadFileName = uploadFileName;

    }

    public String getUsername() {

        return username;

    }

    public String uploadMethod() throws Exception {

//        ServletContext context = ServletActionContext.getServletContext();

//        String real_path = context.getRealPath("/WEB-INF/upload/");

        for (int i = 0; i < upload.length; i++) {

            InputStream inputStream = new FileInputStream(upload[i]);

            OutputStream outputStream = new FileOutputStream(uploadPath + "/" + uploadFileName[i]);

            byte[] b = new byte[1024];

            int len = 0;

            while ((len = inputStream.read(b)) > 0) {

                outputStream.write(b, 0, len);

            }

            // 关闭流

            inputStream.close();

            outputStream.close();

            // 删除tmp文件,最好是用tyrcatch finally进行删除

            // upload[i].delete();

        }

        return SUCCESS;

    }

}

其中文件上传的代码主要引用上一篇文章中的，所以这里主要讲LoginInterceptor.java拦截器的代码分析：

实现Interceptor接口，重写其方法，这里主要注意intercept()方法。这里通过ActionInvocation类型的参数获取session值判断用户是否已经登录。

1）如果没有登录返回值为"toLoginJsp",这里对应upload-interceptor.xml中的result name，将其转发到login.jsp页面；

2）如果已经登录，那么执行上传，但这里需要注意的是，如果返回值为"success"那么将会匹配到配置文件中为result属性为"success"的内容，如果返回值为invocation.invoke(),那么将会执行UploadAction方法，所以这里切记要return invocation.invoke();否则文件上传失败。

其中upload-sturts.xml的配置也是细节问题，主要可以参考文章开头的内容。