七、Struts2之文件上传与下载
一、Struts2文件上传
Struts2的文件上传实现非常简单，只需要简单几步就可完成；
注意：
(1)文件上传的struts2标签为：<s:file name="" label="上传"/>
(2)文件上传的前提是表单属性method="post" enctype="multipart/form-data";
(3)web应用中必须包含common-fileupload.jar和common-io.jar，因为struts2默认上传解析器使用的是jakarta；
(4)可以在struts.xml中配置最大允许上传的文件大小：<constant name="struts.multipart.maxSize" value="....."/>,默认为2M；
1.普通文件上传
实现规则：
(1)在JSP中设定表单控件<s:file name="upload" label="上传"/>
(2)在Action中定义属性：
private File upload; //包含文件内容
private String uploadFileName; //上传文件的名称；
private String uploadContentType; //上传文件的MIME类型；
这些属性都会随着文件的上传自动赋值；
(3)在execute()中完成写入磁盘功能；
代码示例：
Upload01Action.java
package org.upload.action;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionSupport;
public class Upload01Action extends ActionSupport {
private File upload;
private String uploadFileName;
private String uploadContentType;
private String name;
public String execute()throws Exception{
String path = ServletActionContext.getServletContext().getRealPath("/WEB-INF/upload");
String filename = path+File.separator+name;
FileInputStream in = new FileInputStream(upload);
FileOutputStream out = new FileOutputStream(filename);
byte[]b = new byte[1024];
int len = 0;
while((len=in.read(b))>0){
out.write(b,0,len);
}
out.close();
return SUCCESS;
}
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 getUploadContentType() {
return uploadContentType;
}
public void setUploadContentType(String uploadContentType) {
this.uploadContentType = uploadContentType;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
struts.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<constant name="struts.devMode" value="true" />
<constant name="struts.custom.i18n.resources" value="message"></constant>
<package name="default" namespace="/" extends="struts-default">
<action name="upload0*" class="org.upload.action.Upload0{1}Action">
<param name="name">1.jpg</param>
<result>/{1}.jsp</result>
</action>
</package>
</struts>
1.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP '1.jsp' starting page</title>
</head>
<body>
<s:form action="upload01" method="post" enctype="multipart/form-data">
<s:file name="upload" label="上传"></s:file>
<s:submit value="上传"></s:submit>
</s:form>
</body>
</html>
2.利用拦截器进行过滤
手动实现过滤的方式非常简单，就是利用输入校验的方式进行过滤，即在validate()中进行过滤；
而这里要讲的拦截器方式是很好的方式，只需要在配置文件中配置，灵活性很好，能够限制文件的类型、文件的大小；如果上传的文件不符合要求，则返回input逻辑视图；
配置拦截器步骤：
(1)文件上传的拦截器为fileUpload；
(2)需要给定参数allowedTypes、maximumSize;
(3)在fileUpload拦截器后，需要添加<interceptor-ref name="defaultStack"/>
代码示例：
由于通过拦截器进行过滤只需要配置struts.xml，因此这里只给出struts.xml的配置
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<constant name="struts.devMode" value="true" />
<constant name="struts.custom.i18n.resources" value="message"></constant>
<package name="default" namespace="/" extends="struts-default">
<action name="upload0*" class="org.upload.action.Upload0{1}Action">
<interceptor-ref name="fileUpload">
<param name="allowedTypes">image/jpeg,image/gif</param>
<param name="maximumSize">1024*1024</param>
</interceptor-ref>
<interceptor-ref name="defaultStack"></interceptor-ref>
<param name="name">1.jpg</param>
<result>/{1}.jsp</result>
<result name="input">/{1}.jsp</result>
</action>
</package>
</struts>
我们还需要配置文件上传失败后的错误提示信息，我们需要在全局国际化资源文件中配置：
struts.messages.error.content.type.not.allowed=文件类型不匹配 struts.messages.error.file.too.large=文件太大
二、Struts2文件下载
我们在学习Servlet和HTTP协议时已经可以实现文件下载，即写content-disposition头即可，struts2的实现原理也是这个，但是提供了更好的封装性；
struts2的stream结果类型专门用于实现文件下载；
(1)struts.xml中配置stream结果类型，并配置contentType、contentDisposition、bufferSize参数即可，模板：
<action name="download" class=""> <result type="stream" name="success"> <param name="contentType"></param> <param name="contentDisposition">attachment;filename=""</param> <param name="bufferSize">4096</param> </result> </action>
(2)在Action中创建public InputStream getInputStream()throws Exception;方法，此方法用于获得下载文件的输入流；
DownloadAction.java
package org.download.action;
import java.io.InputStream;
import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionSupport;
public class DownloadAction extends ActionSupport {
public InputStream getInputStream()throws Exception{
return ServletActionContext.getServletContext().getResourceAsStream("/WEB-INF/upload/1.jpg");
}
public String execute()throws Exception{
return SUCCESS;
}
}
struts.xml
<action name="download" class="org.download.action.DownloadAction"> <result type="stream" name="success"> <param name="contentType">image/jpeg</param> <param name="contentDisposition">attachment;filename="1.jpg"</param> <param name="bufferSize">4096</param> </result> </action>
就可以完成下载；