Hi all!
I am using Struts from about half a year, and it works good. I have small
webapp using Interbase database by Interclient driver.
When I wanted to use only text data from queries all was fine and simply,
even when "single" jpegs from blob fields. But now I must display some
images on one page and I have some errors with doing that.
My action classes do their work in "normal" way - using database connection
they get data by ResultSets, transfer them to my java beans, and jsp page is
responsible for formatting and displaying this data. But, like I've told it
is related only to text data. All pages till now displayed no more than one
image from database. To achieve that, on required jsp pages is placed
<html:img> tag with proper properties (ie. image id) which is linked to
special action (ImageAction) descendant properly configured in "struts.xml"
file. His work is to:
- extract parameters from request (imageid=87)
- get one-row ResultSet (rs) with image (select image from images where
imageid=87)
- gets this image by rs.getBinaryStream(1)
- copy this stream to ServletOutputStream
- set response mime type and len
- send response by closing its output stream
(code of this class is attached below)
When I need one image on browser page then jsp page contains one tag
<html:img page="/smallImage.do?imageid=87" />. And all works FINE.
SmallImage action simply calls ImageAction. Requests from users goes to
server not often.
But now I need display html-table with five images and this technique not
work. Jsp page contains
<table>
<tr>
<td><html:img page="/smallImage.do?imageid=87" /></td>
<td><html:img page="/smallImage.do?imageid=88" /></td>
</tr>
<tr>
<td><html:img page="/smallImage.do?imageid=89" /></td>
<td><html:img page="/smallImage.do?imageid=90" /></td>
</tr>
</table>
As you see one big change to previous page is that ActionImage class is
called four times to fill one page, and this request goes to server almost
at once.
Errors suggest me, that responsible for this situation goes from ImageAction
to Interclient, but I'm not sure. Generally most frequently I get no images,
sometimes only one image, but never all four required. All images in
database table are in good format, because when I want to get only one image
on page they are displayed correctly.
So I've started my investigation on "How ImageAction doesn't work
correctly". I've put into ImageAction class some additional code to write
out whats going on. I must say that it looks like action gets four request,
starts "simultaneously" create statements, and gets ResultSets. Problems is
when its starts to copy "blob" stream (place is marked in code).
I've get "JDBC IOException: Invalid operation to read on closed blob stream.
See API reference for exception interbase.interclient.BlobIOEception". All
subsequent tries to copy ends with error "[interclient] Client/server
protocol error: Unexpected token in network message received from
Interserver. The internal code is 101. See Api reference for exception
interbase.interclient.RemoteProtocolException". Connection to database is
broken.
QUESTIONS:
1. Is it possible that Interclient driver doesn't support Blobs in
multithread way?
2. Should I change the database engine?
3. Or should I make some trick to collect only one image at a time ? How can
I achieve that ?
4. Or what am I doing wrong? Maybe not synchronizing but I dont understand
this very well.
5. Can anybody help me at all?
My configuration
Tomcat 4.0, Interbase 6.0.1.6 (Open Source)
My code for ImageAction
package jd.struts.images;
import org.apache.struts.action.*;
import javax.servlet.http.*;
import javax.servlet.*;
import java.io.*;
import java.sql.*;
public class ImageAction extends Action {
public ActionForward perform(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response) {
String sParam = request.getParameter("imageid");
try{
Integer iParam = new Integer(sParam);
int i = iParam.intValue();
if (i>0){
HttpSession session=request.getSession();
Connection connection =
(Connection)session.getAttribute("connection");
if (connection!=null){
try {
Statement st = connection.createStatement();
ServletOutputStream sos = httpServletResponse.getOutputStream();
ResultSet rs = st.executeQuery("select image from umowyimages
where umimageid=" + i);
if (rs.next()) {
InputStream is = rs.getBinaryStream(1);
int len = is.available();
<--- here gives back correct blob size
byte b[] = new byte[12];
while (true) {
int bytes = is.read(b);
<--- here appears first error
if (bytes == -1) {
break;
}
else {
len += bytes;
}
sos.write(b, 0, bytes);
}
}
rs.close();
st.close();
response.setContentType("image/jpeg");
response.setContentLength(len);sos.close();
}
catch (Exception ex) {
System.out.println(toString()+"sqlError: "+ex.getMessage());
}
}
else{
System.out.println(toString()+" connectionError");
}
}
else{
System.out.println(toString()+" paramError");
}
}
catch (NumberFormatException nfe) {
System.out.println(toString()+" conversionError");
}
return null;
}
}
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