一个Servlet可以使用HTML表单标记，允许用户上传文件到服务器。上传的文件可能是一个文本文件或图像文件或任何文件。
以下HTM代码创建了一个上载的表单。记下以下重点：
该表格方法，属性应该设置为POST方法，不能使用GET方法。
应该设置表单enctype属性为multipart/form-data。
该表格的action属性应该设置为一个servlet处理文件上传的文件，该文件将在后端服务器。下面的例子是使用UploadServlet的servlet上传文件。
上传单个文件，你应该用一个<input.../>属性type =“file”标签。为了允许多个文件上传，包括一个以上的输入标签具有不同的名称属性的值。
浏览器联关联到他们每个人的“浏览”按钮。
<html>
<head>
<title>File Uploading Form</title>
</head>
<body>
<h3>File Upload:</h3>
Select a file to upload: <br />
<form action="UploadServlet" method="post"
enctype="multipart/form-data">
<input type="file" name="file" size="50" />
<br />
<input type="submit" value="Upload File" />
</form>
</body>
</html>
这将显示下面的结果，这将允许选择一个文件，当用户点击“Upload File”，表单会从本地PC提交选定的文件：
File Upload: Select a file to upload:NOTE: This is just dummy form and would not work.
以下是servlet UploadServlet，会接受上传的文件，并把它储存在目录
<Tomcat-installation-directory>/webapps/data。
这个目录名也可以添加使用外部配置，如context-param元素在web.xml中定义如下：
<web-app>
....
<context-param>
<description>Location to store uploaded file</description>
<param-name>file-upload</param-name>
<param-value>
c:\apache-tomcat-5.5.29\webapps\data\
</param-value>
</context-param>
....
</web-app>
以下是源代码，可以处理多个文件上传的UploadServlet一次。继续操作之前，请确认下列各项：
下面的例子依赖于文件上传，所以一定要确保你有最新版本的的commons-fileupload.x.x.jar文件在你的classpath中。
文件上传依赖于共享IO，所以一定要确保你有最新版本的ofcommons IO-xxjar的文件在你的classpath中。
可以从这里下载 http://commons.apache.org/io/
在测试下面的例子中，你要上传的文件，它有大小不能大于MAXFILESIZE，否则文件将不能上传
请确认已经创建目录c:\temp and c:\apache-tomcat-5.5.29\webapps\data
// Import required java libraries
import java.io.*;
import java.util.*;
import javax.servlet.ServletConfig;
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.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.output.*;
public class UploadServlet extends HttpServlet {
private boolean isMultipart;
private String filePath;
private int maxFileSize = 50 * 1024;
private int maxMemSize = 4 * 1024;
private File file ;
public void init( ){
// Get the file location where it would be stored.
filePath =
getServletContext().getInitParameter("file-upload");
}
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, java.io.IOException {
// Check that we have a file upload request
isMultipart = ServletFileUpload.isMultipartContent(request);
response.setContentType("text/html");
java.io.PrintWriter out = response.getWriter( );
if( !isMultipart ){
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet upload</title>");
out.println("</head>");
out.println("<body>");
out.println("<p>No file uploaded</p>");
out.println("</body>");
out.println("</html>");
return;
}
DiskFileItemFactory factory = new DiskFileItemFactory();
// maximum size that will be stored in memory
factory.setSizeThreshold(maxMemSize);
// Location to save data that is larger than maxMemSize.
factory.setRepository(new File("c:\\temp"));
// Create a new file upload handler
ServletFileUpload upload = new ServletFileUpload(factory);
// maximum file size to be uploaded.
upload.setSizeMax( maxFileSize );
try{
// Parse the request to get file items.
List fileItems = upload.parseRequest(request);
// Process the uploaded file items
Iterator i = fileItems.iterator();
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet upload</title>");
out.println("</head>");
out.println("<body>");
while ( i.hasNext () )
{
FileItem fi = (FileItem)i.next();
if ( !fi.isFormField () )
{
// Get the uploaded file parameters
String fieldName = fi.getFieldName();
String fileName = fi.getName();
String contentType = fi.getContentType();
boolean isInMemory = fi.isInMemory();
long sizeInBytes = fi.getSize();
// Write the file
if( fileName.lastIndexOf("\\") >= 0 ){
file = new File( filePath +
fileName.substring( fileName.lastIndexOf("\\"))) ;
}else{
file = new File( filePath +
fileName.substring(fileName.lastIndexOf("\\")+1)) ;
}
fi.write( file ) ;
out.println("Uploaded Filename: " + fileName + "<br>");
}
}
out.println("</body>");
out.println("</html>");
}catch(Exception ex) {
System.out.println(ex);
}
}
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, java.io.IOException {
throw new ServletException("GET method used with " +
getClass( ).getName( )+": POST method required.");
}
}
编译以上的servlet UploadServlet和在web.xml文件中配置如下创建所需的条目
<servlet> <servlet-name>UploadServlet</servlet-name> <servlet-class>UploadServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>UploadServlet</servlet-name> <url-pattern>/UploadServlet</url-pattern> </servlet-mapping>
现在尝试使用HTML表格，你在上面创建的文件上传。当在浏览器中访问：http://localhost:8080/UploadFile.htm时，它会显示下面的结果，这将有助于你从本地计算机上传任何文件。
File Upload: Select a file to upload:
如果servelt脚本能正常工作，可以上传文件应该在 c:\apache-tomcat-5.5.29\webapps\data\ 目录中.