response.setContentType("image/jpeg");
os = response.getOutputStream();
os.write(((ByteArrayOutputStream) cos).toByteArray());
//os2 = new FileOutputStream("D:/ss.jpg");
//os2.write(((ByteArrayOutputStream) cos).toByteArray());
response.flushBuffer();
Environment: windows2003, Tomcat5.5, jfreechart1.0.9/11.
Symptom: The image(jpg) generated by jfreechart cannot be shown in IE(Red X), but correctly shown in firefox and also correctly saved in harddisk.
Solution: Use a older version jfreechart such as 1.0.2 or 5.
Sum-up: Take the open source as the code writen by myself, there are many bugs hidden in them too.