java中struts2实现简单的文件上传与下载

时间:2022-08-30 16:33:27

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

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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

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<?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

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<%@ 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

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<?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:

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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:

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<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

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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

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<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。

java中struts2文件上传下载的实现就为大家介绍到这里,谢谢大家的阅读。