从数据库中读取并生成图片的Servlet

发布: 2007-7-01 18:47 | 作者: admin | 来源: | 查看: 18次 | 进入软件测试论坛讨论

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() {
  }
}