Image is not displayed from Oracle table using servlet

问题

After a long trial ,I finally successfully able to upload an image to an oracle database. At least my code says so. However to check whether the image has been successfully I wrote a servlet. After running the servlet I get a black screen in my browser and nothing else. The servlet code is:

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DisplayImage extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException  {
    // TODO Auto-generated method stub
     try {
         Class.forName("oracle.jdbc.driver.OracleDriver");  
         String url = "jdbc:oracle:thin:@localhost:1521:XE";
         Connection con = DriverManager.getConnection(url,"system","root");
            PreparedStatement ps = con.prepareStatement("select image from insertimage");
            ResultSet rs = ps.executeQuery();
            rs.next();
            Blob  b = rs.getBlob("image");
            response.setContentType("image/jpeg");
            response.setContentLength( (int) b.length());
            InputStream is = b.getBinaryStream();
            OutputStream os = response.getOutputStream();
            byte buf[] = new byte[(int) b.length()];
            is.read(buf);
            os.write(buf);
            os.close();
        }
        catch(Exception ex) {
             System.out.println(ex.getMessage());
        }
    } 

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    } 
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
}

  }

By the way, as I am totally new to this, I took extensive help from this File upload and display demo. EDIT : I get the black screen if only viewed from FF , but if viewed from internal web browser of Eclipse it shows me a single word upload . Very strange behaviour!!

回答1:

Use a debugger, or traces in the code, to see what it executes.

Use Firebug to see what the response contains.

And fix the reading and writing from the blob to the output stream: InputStream.read() doesn't necessarily read all the bytes at once. It returns the number of bytes that were actually read. You should loop until this method returns -1 to indicate that everything has been read. Read the Java IO tutorial.

来源：https://stackoverflow.com/questions/11724624/image-is-not-displayed-from-oracle-table-using-servlet