GWT 实现文件上传和下载

首先下载两个包 commons-fileupload-?.jar和commons-io-?.jar  将他们配置到你的项目中

上传代码:

client 端代码:

final FileUpload fileUpload = new FileUpload();
final FormPanel formpanel = new FormPanel();

fileUpload.setName("uploadFormElement");
		formpanel.setEncoding( FormPanel.ENCODING_MULTIPART );
		formpanel.setMethod( FormPanel.METHOD_POST );
		formpanel.setAction( GWT.getModuleBaseURL() + "fileupload" );
		formpanel.setWidget( fileUpload );
		
		uploadbutton.addClickHandler( new ClickHandler() {
			public void onClick( ClickEvent sender ) {
				formpanel.submit();
			}
		});
		formpanel.addSubmitHandler( new SubmitHandler() {
			public void onSubmit(SubmitEvent event) {
				if( fileUpload.getFilename().length() == 0 ) {
					Window.alert( "you must select a file" );
				}
				
			}
		});
		formpanel.addSubmitCompleteHandler( new SubmitCompleteHandler() {
			public void onSubmitComplete(SubmitCompleteEvent event) {
				//兼容linux文件分隔符?
				String selected = fileUpload.getFilename().replaceAll("/", "//");
				selected = selected.substring( selected.lastIndexOf("//")+1);
								Window.alert( "upload complete"+ event.getResults());
			}
		});

之后再server中添加服务 :FileUploadServlet.java

package sample.server;


import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;
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.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

public class FileUploadServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	
	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException {
	// TODO Auto-generated method stub
	
		response.setContentType("text/html");
		response.setCharacterEncoding("utf-8"); 
		FileItemFactory factory = new DiskFileItemFactory();
		ServletFileUpload upload = new ServletFileUpload(factory);     
    
		List items = null;     

		try {    
			items = upload.parseRequest(request);     
		}
		catch (FileUploadException ex) {     
			ex.printStackTrace();     
		}    
    
		Iterator iter = items.iterator();     
    
		while (iter.hasNext()) {     
			FileItem item = (FileItem) iter.next();     
     
			String savePath = getServletContext().getRealPath("/uploads");
    	                    
			String filename = item.getName();	
   
			String filename2 = filename.replaceAll("/", "//");
			int pos = filename.lastIndexOf( "//") + 1;
   
			File file = new File(savePath,filename.substring( pos ) ); 
    	 
			try {
				item.write(file);
			} 
			catch (Exception e) {	
				e.printStackTrace();
			}    
		}     
	}    
}

 打开web.xml 加入

<servlet>
    <servlet-name>uploadServlet</servlet-name>
    <servlet-class>xxx.xxx.FileUploadServlet</servlet-class>
  </servlet>
  
  <servlet-mapping>
    <servlet-name>uploadServlet</servlet-name>
    <url-pattern>fileupload</url-pattern>
  </servlet-mapping>

两个servlet-name 相同即可 而servlet-class对应之前添加的服务，url-pattern对应 client端中的

formpanel.setAction( GWT.getModuleBaseURL() + "fileupload" );

打开 xxx.gwt.xml 加入 ：<servlet class="sample.server.FileUploadServlet" path="/fileupload" />

class 和 path也是对应的，别搞错。

下载代码;

client中代码：

void download( String filename ) {
		if( RootPanel.get("downloadiframe") != null ) {
			Widget widgetFrame = (Widget)RootPanel.get("downloadiframe");
			widgetFrame.removeFromParent();
		} 
		Frame frame = new Frame( GWT.getModuleBaseURL() + "filedownload" + "?id=downloadiframe"+
				"&filename=" + filename );
		frame.setVisible( false );
		frame.setSize( "0px", "0px" );
		RootPanel.get().add( frame );
		
	}

服务器server:DownloadServlet.java

package sample.server;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

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

import com.google.gwt.core.client.GWT;
import com.google.gwt.user.client.ui.Frame;

public class DownloadServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	protected void doGet( HttpServletRequest req, HttpServletResponse resp )
		throws ServletException, IOException
	{
		//此函数对应之前的 Frame frame = 
		//new Frame( GWT.getModuleBaseURL() + "filedownload" + "?id=downloadiframe"+"&filename=" + filename );
		//传文件名那个简单啊
		String filename = req.getParameter("filename");
		
		//这边你要自己决定从哪下载的文件！！ 我是把上传路径直接给他了
		//这里说下。。我先前没自己创建 uploads 结果十分悲剧
		//记得在 war 路径下创建 ！！
		String filepath = req.getRealPath("/uploads");
		File file = new File( filepath+"/"+filename );

		//下面代码从网上拉的，直接抄就行了
		FileInputStream fis = new FileInputStream(file);
		resp.addHeader("Content-Disposition","attachment; filename=" + filename );

		ServletOutputStream out = resp.getOutputStream();
		resp.setBufferSize(32768);
		int bufSize = resp.getBufferSize();
		byte[] buffer = new byte[bufSize];
		BufferedInputStream bis = new BufferedInputStream(fis,bufSize);

		int bytes;
		while ((bytes = bis.read(buffer, 0, bufSize)) >= 0)
			out.write(buffer, 0, bytes);
		bis.close();
		fis.close();
		out.flush();
		out.close();
	}
}

配置两个xml和upload是一样的,在此不赘述。