servlet如何实现从数据库blob字段读取文件并显示

原创|其它|编辑:郝浩|2009-06-30 10:43:00.000|阅读 850 次

概述:本文介绍用servlet实现从数据库blob字段读文件并显示的方法。

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 /*
  * ReadFile.Java
  */
  package jgwl.app;
  import java.io.*;
  import java.net.*;
  import javax.Servlet.*;
  import javax.servlet.http.*;
  import java.sql.*;
  import jgwl.base.DataBaseConnection;
  import java.io.*;
  import Oracle.sql.*;

  public class ReadFile extends HttpServlet {
  /** Initializes the servlet.
  */
  public void init(ServletConfig config) throws ServletException {
  super.init(config);
  }
  /** Destroys the servlet.
  */
  public void destroy() {
  }
  /** Processes requests for both HTTP GET and POST methods.
  * @param request servlet request
  * @param response servlet response
  */
  protected void processRequest(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
  byte[] buf=new byte[4096];
  try{
  Statement stmt=new DataBaseConnection().getStatement();
  ResultSet rs=stmt.executeQuery("select * from demo where id=23");
  response.reset();
  //response.setHeader("Content-Disposition", "attachement;filename=ss.doc;");
  //**如要浏览器直接另存为就不屏蔽上行,filename 为文件名
  response.setContentType("application/msword;charset=GBK");
  //**此处为文件的mime类型,可以在网上搜到,本例为word
  //application/vnd.ms-Excel;charset=GBK 表示excel文件类型
  //application/vnd.pdf;charset=GBK      表示pdf文件类型
  ServletOutputStream out=response.getOutputStream();
  InputStream in;
  if(rs.next())
  in = blob.getBinaryStream();
  while(in.read(buf)!=-1){
  out.write(buf);
  }
  out.flush();
  out.close();
  //**以下为网上看到的写如文件的样例
  //==================
  // while(rs.next()) {
  //ServletOutputStream sout = response.getOutputStream();
  //InputStream in = rs.getBinaryStream(1);
  //byte b[] = new byte[0x7a120];
  //for(int i = in.read(b); i != -1;){
  // sout.write(b);
  // in.read(b);
  // }
  // sout.flush();
  // sout.close();
  //}
  //====================
  //FileOutputStream file_out=new FileOutputStream("f:filename");
  //InputStream blob_in=blob.getBinaryStream();
  //int temp;
  // while((temp=blob_in.read())!=-1){
  // file_out.write(temp);}
  // blob_in.close();
  // file_out.close();
  //out.write(blob.getBinaryStream().);
  //out.flush();
  stmt.close();
  }catch (SQLException e){
  e.printStackTrace();
  }
  //PrintWriter out = response.getWriter();
  /* TODO output your page here
  out.println("");
  out.println("");
  out.println("");
  out.println("");
  out.println("");
  out.println("");
  out.println("");
  */
  //out.close();
  }
  /** Handles the HTTP GET method.
  * @param request servlet request
  * @param response servlet response
  */
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
  processRequest(request, response);
  }
  /** Handles the HTTP POST method.
  * @param request servlet request
  * @param response servlet response
  */
  protected void doPost(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
  processRequest(request, response);
  }
  /** Returns a short description of the servlet.
  */
  public String getServletInfo() {
  return "Short description";
  }
  }


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