<!-- Struts核心拦截器 -->
    <filter>
        <filter-name>Struts2</filter-name>
        <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>Struts2</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

import java.io.File;
import org.apache.commons.io.FileUtils;
import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionSupport;

public class FileUpload extends ActionSupport {

    // 对应表单：<input type="file" name="file1">
    private File file1;
    // 文件名
    private String file1FileName;
    // 文件的类型(MIME)
    private String file1ContentType;

    public void setFile1(File file1) {
        this.file1 = file1;
    }

    public void setFile1FileName(String file1FileName) {
        this.file1FileName = file1FileName;
    }

    public void setFile1ContentType(String file1ContentType) {
        this.file1ContentType = file1ContentType;
    }

    @Override
    public String execute() throws Exception {
        /****** 拿到上传的文件，进行处理 ******/
        // 把文件上传到upload目录

        // 获取上传的目录路径
        String path = ServletActionContext.getServletContext().getRealPath(
                "/upload");
        // 创建目标文件对象
        File destFile = new File(path, file1FileName);
        // 把上传的文件，拷贝到目标文件中
        FileUtils.copyFile(file1, destFile);

        return SUCCESS;
    }
}

package com.yif.fileupload;

import java.io.File;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.Map;
import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionSupport;

public class DownAction extends ActionSupport {
    
    /*************1. 显示所有要下载文件的列表*********************/
    public String list() throws Exception {
        //得到upload目录路径
        String path = ServletActionContext.getServletContext().getRealPath("/upload");
        // 目录对象
        File file  = new File(path);
        // 得到所有要下载的文件的文件名
        String[] fileNames =  file.list();
        // 保存
        ActionContext ac = ActionContext.getContext();
        // 得到代表request的map (第二种方式)
        Map<String,Object> request= (Map<String, Object>) ac.get("request");
        request.put("fileNames", fileNames);
        return "list";
    }
    
    /*************2. 文件下载*********************/
    private String fileName;
    public void setFileName(String fileName) {
        // 处理传入的参数中问题(get提交)
        try {
            fileName = new String(fileName.getBytes("ISO8859-1"),"UTF-8");
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e);
        }
        // 把处理好的文件名，赋值
        this.fileName = fileName;
    }
    
    //2. 下载提交的业务方法 (在struts.xml中配置返回stream)
    public String down() throws Exception {
        return "download";
    }
    
    // 3. 返回文件流的方法
    public InputStream getAttrInputStream(){
        return ServletActionContext.getServletContext().getResourceAsStream("/upload/" + fileName);
    }
    
    // 4. 下载显示的文件名（浏览器显示的文件名）
    public String getDownFileName() {
        // 需要进行中文编码
        try {
            fileName = URLEncoder.encode(fileName, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e);
        }
        return fileName;
    }

    
}

<?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="upload_" extends="struts-default">
        <!-- 注意： action 的名称不能用关键字"fileUpload" -->
        <action name="fileUploadAction" class="com.yif.fileupload.FileUpload">
            <!-- 限制运行上传的文件的类型 -->
            <interceptor-ref name="defaultStack">
                <!-- 限制运行的文件的扩展名 -->
                <param name="fileUpload.allowedExtensions">txt,jpg,jar</param>
                <!-- 限制运行的类型 【与上面同时使用，取交集】 <param name="fileUpload.allowedTypes">text/plain</param> -->
            </interceptor-ref>
            <result name="success">/e/success.jsp</result>
            <!-- 配置错误视图 -->
            <result name="input">/e/error.jsp</result>
        </action>
        <action name="down_*" class="com.yif.fileupload.DownAction"
            method="{1}">
            <!-- 列表展示 -->
            <result name="list">/e/list.jsp</result>
            <!-- 下载操作 -->
            <result name="download" type="stream">
                <!-- 运行下载的文件的类型:指定为所有的二进制文件类型 -->
                <param name="contentType">application/octet-stream</param>
                <!-- 对应的是Action中属性： 返回流的属性【其实就是getAttrInputStream()】 -->
                <param name="inputName">attrInputStream</param>

                <!-- 下载头，包括：浏览器显示的文件名 -->
                <param name="contentDisposition">attachment;filename=${downFileName}</param>
                <!-- 缓冲区大小设置 -->
                <param name="bufferSize">1024</param>
            </result>
        </action>
    </package>
</struts>

<?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="com/yif/fileupload/upload.xml"></include>
</struts>