java中struts2实现简单的文件上传与下载

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。

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。

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