从数据库中读取并生成图片的Servlet

王朝other·作者佚名  2008-05-31
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从数据库中读取并生成图片的Servlet

大体思路

1)创建ServletOutputStream对象out,用于以字节流的方式输出图像

2)查询数据库,用getBinaryStream方法返回InputStream对象in

3)创建byte数组用作缓冲,将in读入buf[],再由out输出

注:下面的例程中数据库连接用了ConnectionPool,以及参数的获得进行了预处理

package net.seasky.music;

import Javax.servlet.*;

import javax.servlet.http.*;

import java.io.*;

import java.util.*;

import java.sql.*;

import net.seasky.util.*;

import net.seasky.database.DbConnectionManager;

public class CoverServlet extends HttpServlet {

private static final String CONTENT_TYPE = "image/gif";

public void init(ServletConfig config) throws ServletException {

super.init(config);

}

public void doGet(HttpServletRequest request, HttpServletResponse response

) throws ServletException, IOException {

response.setContentType(CONTENT_TYPE);

int albumID;

ServletOutputStream out = response.getOutputStream();

try {

albumID = ParamManager.getIntParameter(request,"albumID",0);

}

catch (Exception e) {

response.sendRedirect("../ErroePage.jsp");

return;

}

try {

InputStream in=this.getCover(albumID);

int len;

byte buf[]=new byte[1024];

while ((len=in.read(buf,0,1024))!=-1) {

out.write(buf,0,len);

}

}

catch (IOException ioe) {

ioe.printStackTrace() ;

}

}

private InputStream getCover(int albumID) {

InputStream in=null;

Connection cn = null;

PreparedStatement pst = null;

try {

cn=DbConnectionManager.getConnection();

cn.setCatalog("music");

pst=cn.prepareStatement("SELECT img FROM cover where ID =?");

pst.setInt(1,albumID);

ResultSet rs=pst.executeQuery();

rs.next() ;

in=rs.getBinaryStream("img");

}

catch (SQLException sqle) {

System.err.println("Error in CoverServlet : getCover()-" + sqle);

sqle.printStackTrace() ;

}

finally {

try {

pst.close() ;

cn.close() ;

}

catch (Exception e) {

e.printStackTrace();

}

}

return in;

}

public void destroy() {

}

}

 
 
 
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