commons-fileupload

对于实现文件上传功能来说，Commons-fileupload组件是一个不错的选择

    
        <!-- enctype属性为表单定义了MIME编码方式，上传文件的表单enctype属性必须如此设置 -->
            <form method="post" action="UploadFile" enctype="multipart/form-data" >
            <p><input type="text" name="fileIntro" value="" />文件介绍</p>
            <p><input type="file" name="myfile1" value="浏览文件" /></p>
            <p><input type="submit" value="上传"/></p>
            </form>

Servlet代码

import java.io.File;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

import com.sitinspring.util.UploadUtil;

/**
 * 用于文件上传处理的Servlet
 * @author sitinspring
 *
 * @date 2008-2-12
 */
public class UploadFileServlet extends HttpServlet {
    private static final long serialVersionUID = 56890894234786L;

    @SuppressWarnings("unchecked")
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, java.io.IOException {
        request.setCharacterEncoding("UTF-8");

        // 文件上傳部分
        boolean isMultipart = ServletFileUpload.isMultipartContent(request);
        
        if (isMultipart == true) {
            try {
                FileItemFactory factory = new DiskFileItemFactory();
                ServletFileUpload upload = new ServletFileUpload(factory);
                
                // 得到所有的表单域，它们目前都被当作FileItem
                List<FileItem> fileItems = upload.parseRequest(request);
                Iterator<FileItem> iter = fileItems.iterator();
                
                // 依次处理每个表单域
                while (iter.hasNext()) {
                    FileItem item = (FileItem) iter.next();
                    
                    if(item.isFormField()){
                        // 如果item是正常的表单域
                        String name = item.getFieldName();
                        String value = item.getString();
                        System.out.print("表单域名为:"+name+"表单域值为:"+value);
                    }
                    else{
                        // 如果item是文件上传表单域
                        
                        // 获得文件名及路径
                        String fileName = item.getName();
                        if (fileName != null) {
                            File fullFile = new File(item.getName());                            
                                                        
                            // 如果文件存在则上传
                            if(fullFile.exists()){
                                File fileOnServer = new File(UploadUtil.getUploadPath(),
                                        fullFile.getName());
                                item.write(fileOnServer);
                                
                                System.out.println("文件"+fileOnServer.getName()+"上传成功");
                            }
                        }
                    }
                }                
            } catch (Exception e) {
                e.printStackTrace();
            }
        } else {
            System.out.println("the enctype must be multipart/form-data");
        }
        
        // 取得服务器中已有文件的下載列表
        List<String> fileListInServer=new ArrayList<String>(); 
        
        File dir = new File(UploadUtil.getUploadPath());        
        String[] children = dir.list();
        if (children != null) {
            for (int i=0; i<children.length; i++) {
                fileListInServer.add(children[i]);                
            }
        }
        
        request.setAttribute("downloadList", fileListInServer);

        // 跳回原頁面
        RequestDispatcher dispatcher = request
                .getRequestDispatcher("/web/page/uploadtoserver.jsp");
        dispatcher.forward(request, response);
        return;
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, java.io.IOException {
        doPost(request, response);
    }
}

从上面的代码可以看出，无论是否文件上传表单域都被当成了FileItem来处理，要区别开来使用isFormField()方法即可，返回真是常规表单域，返回假则是文件上传表单域。

2.多个文件上传到服务器端。

这里采用JS动态生成几个文件上传表单域即可，Servlet无需改变。
多文件上传页面代码如下:

<%@pagecontentType="text/html;charset=UTF-8"%>
<%@pagelanguage="java"import="java.util.List"%>

<!DOCTYPEHTMLPUBLIC"-//W3C//DTDHTML4.0Transitional//EN">
<html>
<head>
<title>上传多個文件到服务器</title>
<metahttp-equiv="Content-Type"content="text/html;charset=UTF-8">
<linkrel="stylesheet"rev="stylesheet"href="web/css/style.css"
type="text/css"/>
</head>

<body>
<divid="bodyDiv">
<divid="header">
<jsp:includepage="/web/page/branch/header.jsp"/>
</div>
<divid="sidebar">
<jsp:includepage="/web/page/branch/sidebar.jsp"/>
</div>
<divid="content">
<fieldset><legend>下載列表</legend>
<ul>
<%
List<String>downloadList=(List<String>)request.getAttribute("downloadList");

if(downloadList!=null){
for(Stringstr:downloadList){
out.print("<li><ahref='DownloadFile?file="+str+"'>"+str+"</a></li>");
}
}
%>
</ul>
</fieldset>

<!--enctype属性为表单定义了MIME编码方式，上传文件的表单enctype属性必须如此设置-->
<formname="uploadForm"method="post"action="UploadFile"enctype="multipart/form-data">
<p><inputtype="button"value="增加上传按钮"onclick="addUploadButton()"/></p>
<p><inputtype="file"name="myfile1"value="浏览文件"/></p>
<p><inputtype="submit"value="上传"/></p>
</form>
</div>
<divid="footer">
<jsp:includepage="/web/page/branch/footer.jsp"/>
</div>
</div>
</body>

JS代码：

<scriptLANGUAGE="JavaScript">
<!--
varcount=1;

functionaddUploadButton(){
//按ID找到FOrm
varuploadForm=document.getElementById("uploadForm");

//创建P元素
varpNode=document.createElement("p");

//累加Count以观察次数
count=count+1;

pNode.innerHTML="<inputtype='file'name='myfile"+count+"'value='浏览文件'/>";

//将P元素添加到body中
uploadForm.appendChild(pNode);
}

//-->
</script>
</html>