Java Servlet 编程及应用之八

核心提示：java Servlet 在网络上的编程应用，如利用Servlet 上传和下载文件、Servlet 的数据库编程、在Servlet 中发送和接受邮件以及Java Servlet 在RMI和xml等方面的应用，Java Servlet 编程及应用之八，由于篇幅有限，在这里就不在多介绍了，其主要功能为从InputStrea

　　java Servlet 在网络上的编程应用，如利用Servlet 上传和下载文件、Servlet 的数据库编程、在Servlet 中发送和接受邮件以及Java Servlet 在RMI和xml等方面的应用，由于篇幅有限，在这里就不在多介绍了，下面再举一个Servlet 上传的例子。

　　在Web 应用程序中，用户向服务器上传文件是非常普遍的操作。使用Servlet 实现文件的上传是比较简单的。

　　编程思路：下面的UploadServlet.java ，其主要功能为从InputStream 中读取文件内容，将上传文件保存在根目录下，且文件名与上传文件的文件名一致。

　　UploadServlet.java 的源代码如下：(代码节选)

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class UploadServlet extends HttpServlet
{
//default maximum allowable file size is 1000k
static final int MAX_SIZE = 1024000;
//instance variables to store root and sUCcess message
String rootPath, successMessage;
/**
* init method is called when servlet is initialized.
*/
public void init(ServletConfig config) throws ServletException
{
super.init(config);
//get path in which to save file
rootPath = config.getInitParameter("RootPath");
if (rootPath == null)
{
rootPath = "/";
}
/*Get message to show when upload is complete. Used only if
a success redirect page is not supplied.*/
successMessage = config.getInitParameter("SuccessMessage");
if (successMessage == null)
{
successMessage = "File upload complete!";
}
}
/**
* doPost reads the uploaded data from the request and writes
* it to a file.
*/
public void doPost(HttpServletRequest request,
HttpServletResponse response)
{
ServletOutputStream out=null;
DataInputStream in=null;
FileOutputStream fileOut=null;

try
{
/*set content type of response and get handle to output
stream in case we are unable to redirect client*/
response.setContentType("text/plain");
out = response.getOutputStream();

//get content type of client request
String contentType = request.getContentType();
out.PRintln("\ncontentType= " + contentType);

//make sure content type is multipart/form-data
if(contentType != null && contentType.indexOf(
"multipart/form-data") != -1)
{
//open input stream from client to capture upload file
in = new DataInputStream(request.getInputStream());
//get length of content data
int formDataLength = request.getContentLength();
out.println("\nContentLength= " + formDataLength);

//allocate a byte array to store content data
byte dataBytes[] = new byte[formDataLength];
//read file into byte array
int bytesRead = 0;
int totalBytesRead = 0;
int sizeCheck = 0;
while (totalBytesRead ＜ formDataLength)
{
//check for maximum file size violation
sizeCheck = totalBytesRead + in.available();
if (sizeCheck ＞ MAX_SIZE)
{
out.println("Sorry, file is too large to upload.");
return;
}

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