I am seeing strange behaviour with a servlet I wrote to return an image
from a database table. I'm not sure if it's struts related or not, but I
am relying on a datasource defined in the struts-config.xml. It might be
a silly mistake in the servlet code itself even.
I've attached the struts-config.xml which shows my datasource
definition, the web.xml where I define the servlet and provide an
initialization parameter, the servlet code (PhotoServlet.java) and a
simple test.jsp page.
The code I have seems to work most of the time (about 25/30 requests)
before failing a couple of times. The log.txt attachment shows the
result of doing:
while true
do
lwp-request \
'http://localhost:8080/shona/servlets/photo?id=1&class=thumbnail' \
| wc -c
done
(just sequential requests)
The error.txt attachment shows the exception information generated when
a request fails. Note there seem to be two types of exceptions occuring
here: a low level jdbc error, and a "no results returned" error.
I've played with the maxCount and minCount parameters in the struts
datasource definition. Same results, except in the case of several
simultaneous requests to the servlet -- in which case raising maxCount
seems to prolong the interval between exceptions.
It's really been baffling me for a while now. What could be going wrong?
Am I seeing a limitation of Struts' connection pool perhaps? Even if
it's not struts related, suggestions would still be very welcome.
Matt
/*
* PhotoServlet.java
*
* Created on February 23, 2002, 2:53 AM
*/
package mbkennedy.pshop.servlets;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.sql.*;
import java.io.*;
import java.sql.*;
/**
*
* @author mkennedy
* @version
*/
public class PhotoServlet extends org.apache.struts.action.ActionServlet {
private static final long DEFAULT_BUFFER_SIZE = 1024;
/**
* bufferSize to use when transfering blob to servlet response.
*/
private long bufferSize;
private DataSource dataSource = null;
/**
* Initializes the servlet.
*/
public void init(ServletConfig config) throws ServletException {
super.init(config);
String bufferSizeParam = null;
if ((bufferSizeParam = config.getInitParameter("bufferSize")) != null) {
// Servlet deployer intends to override default bufferSize
this.bufferSize = Long.parseLong(config.getInitParameter("bufferSize"));
if (this.bufferSize <= 0) {
throw new ServletException("bufferSize must be > 0: bufferSize == " +
this.bufferSize);
}
} else {
this.bufferSize = this.DEFAULT_BUFFER_SIZE;
}
dataSource = this.findDataSource("default");
}
/**
* Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.
*
* @param request servlet request
* @param response servlet response
*/
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// Check request parameters
if (request.getParameter("id") == null || request.getParameter("class") == null) {
throw new ServletException("invalid request parameters: id = " +
request.getParameter("id") + ", class = " + request.getParameter("class"));
}
// Validate parameters
int paramId = 0;
try {
paramId = Integer.parseInt(request.getParameter("id"));
} catch (NumberFormatException e_nf) {
throw (ServletException) new ServletException("id must be an integer: id = " +
request.getParameter("id")).initCause(e_nf);
}
Connection conn = null;
try {
String paramClass = null;
conn = this.dataSource.getConnection();
PreparedStatement stmt1 =
conn.prepareStatement("SELECT class FROM image_class WHERE class = ?");
stmt1.setString(1, request.getParameter("class"));
if (stmt1.executeQuery().getFetchSize() == 0) {
throw new ServletException("class is invalid: class = " +
request.getParameter("class"));
} else {
paramClass = request.getParameter("class");
}
stmt1.close();
// At this point parameters have been validated for correctness (it
// should be safe to process the request)
PreparedStatement stmt2 = conn.prepareStatement("SELECT image, mime_type " +
"FROM item_photos WHERE (item_id = ?) AND (image_class = ?)");
stmt2.setInt(1, paramId);
stmt2.setString(2, paramClass);
ResultSet results = stmt2.executeQuery();
ServletOutputStream out = response.getOutputStream();
if (results.getFetchSize() == 0) {
out.close();
} else {
// TODO: Handle multiple photos for a single pruduct
results.first();
Blob blob = results.getBlob("image");
long length = blob.length();
long chunks = length / this.bufferSize;
long remainder = length % this.bufferSize;
response.setContentType(results.getString("mime_type"));
long pos = 0;
for (long i = 0; i < chunks; i++, pos += this.bufferSize) {
out.write(blob.getBytes(pos, (int) this.bufferSize));
}
out.write(blob.getBytes(pos, (int) remainder));
out.close();
}
stmt2.close();
} catch (SQLException e_sql) {
throw (ServletException)
new ServletException("SQL error").initCause(e_sql);
} finally {
if (conn != null) {
try {
conn.close();
} catch (SQLException e_sql) {
}
}
}
}
/**
* Handles the HTTP <code>GET</code> method.
*
* @param request servlet request
* @param response servlet response
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, java.io.IOException {
processRequest(request, response);
}
/**
* Handles the HTTP <code>POST</code> method.
*
* @param request servlet request
* @param response servlet response
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, java.io.IOException {
processRequest(request, response);
}
/**
* Returns a short description of the servlet.
*/
public String getServletInfo() {
return "Servlet to return photo images from the database.";
}
}
2002-03-10 02:10:14 - Ctx( /shona ): Exception in: R( /shona + /servlets/photo + null)
- javax.servlet.ServletException: SQL error
at mbkennedy.pshop.servlets.PhotoServlet.processRequest(PhotoServlet.java:121)
at mbkennedy.pshop.servlets.PhotoServlet.doGet(PhotoServlet.java:141)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:404)
at org.apache.tomcat.core.Handler.service(Handler.java:286)
at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
at
org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:797)
at org.apache.tomcat.core.ContextManager.service(ContextManager.java:743)
at
org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:210)
at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:498)
at java.lang.Thread.run(Thread.java:536)
Caused by: No results were returned by the query.
at org.postgresql.jdbc2.Statement.executeQuery(Unknown Source)
at org.postgresql.jdbc2.PreparedStatement.executeQuery(Unknown Source)
at mbkennedy.pshop.servlets.PhotoServlet.processRequest(PhotoServlet.java:81)
... 12 more
2002-03-10 02:10:44 - Ctx( /shona ): Exception in: R( /shona + /servlets/photo + null)
- javax.servlet.ServletException: SQL error
at mbkennedy.pshop.servlets.PhotoServlet.processRequest(PhotoServlet.java:121)
at mbkennedy.pshop.servlets.PhotoServlet.doGet(PhotoServlet.java:141)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:404)
at org.apache.tomcat.core.Handler.service(Handler.java:286)
at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
at
org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:797)
at org.apache.tomcat.core.ContextManager.service(ContextManager.java:743)
at
org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:210)
at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:498)
at java.lang.Thread.run(Thread.java:536)
Caused by: No results were returned by the query.
at org.postgresql.jdbc2.Statement.executeQuery(Unknown Source)
at org.postgresql.jdbc2.PreparedStatement.executeQuery(Unknown Source)
at mbkennedy.pshop.servlets.PhotoServlet.processRequest(PhotoServlet.java:81)
... 12 more
2002-03-10 02:11:29 - Ctx( /shona ): Exception in: R( /shona + /servlets/photo + null)
- javax.servlet.ServletException: SQL error
at mbkennedy.pshop.servlets.PhotoServlet.processRequest(PhotoServlet.java:121)
at mbkennedy.pshop.servlets.PhotoServlet.doGet(PhotoServlet.java:141)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:404)
at org.apache.tomcat.core.Handler.service(Handler.java:286)
at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
at
org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:797)
at org.apache.tomcat.core.ContextManager.service(ContextManager.java:743)
at
org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:210)
at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:498)
at java.lang.Thread.run(Thread.java:536)
Caused by: FastPath call returned ERROR: current transaction is aborted, queries
ignored until end of transaction block
at org.postgresql.fastpath.Fastpath.fastpath(Unknown Source)
at org.postgresql.fastpath.Fastpath.fastpath(Unknown Source)
at org.postgresql.fastpath.Fastpath.getInteger(Unknown Source)
at org.postgresql.largeobject.LargeObject.<init>(Unknown Source)
at org.postgresql.largeobject.LargeObjectManager.open(Unknown Source)
at org.postgresql.largeobject.PGblob.<init>(Unknown Source)
at org.postgresql.jdbc2.ResultSet.getBlob(Unknown Source)
at org.postgresql.jdbc2.ResultSet.getBlob(Unknown Source)
at mbkennedy.pshop.servlets.PhotoServlet.processRequest(PhotoServlet.java:104)
... 12 more
2002-03-10 02:11:52 - Ctx( /shona ): Exception in: R( /shona + /servlets/photo + null)
- javax.servlet.ServletException: SQL error
at mbkennedy.pshop.servlets.PhotoServlet.processRequest(PhotoServlet.java:121)
at mbkennedy.pshop.servlets.PhotoServlet.doGet(PhotoServlet.java:141)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:404)
at org.apache.tomcat.core.Handler.service(Handler.java:286)
at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
at
org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:797)
at org.apache.tomcat.core.ContextManager.service(ContextManager.java:743)
at
org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:210)
at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:498)
at java.lang.Thread.run(Thread.java:536)
Caused by: FastPath call returned ERROR: current transaction is aborted, queries
ignored until end of transaction block
at org.postgresql.fastpath.Fastpath.fastpath(Unknown Source)
at org.postgresql.fastpath.Fastpath.fastpath(Unknown Source)
at org.postgresql.fastpath.Fastpath.getInteger(Unknown Source)
at org.postgresql.largeobject.LargeObject.<init>(Unknown Source)
at org.postgresql.largeobject.LargeObjectManager.open(Unknown Source)
at org.postgresql.largeobject.PGblob.<init>(Unknown Source)
at org.postgresql.jdbc2.ResultSet.getBlob(Unknown Source)
at org.postgresql.jdbc2.ResultSet.getBlob(Unknown Source)
at mbkennedy.pshop.servlets.PhotoServlet.processRequest(PhotoServlet.java:104)
... 12 more
2002-03-10 02:11:53 - Ctx( /shona ): Exception in: R( /shona + /servlets/photo + null)
- javax.servlet.ServletException: SQL error
at mbkennedy.pshop.servlets.PhotoServlet.processRequest(PhotoServlet.java:121)
at mbkennedy.pshop.servlets.PhotoServlet.doGet(PhotoServlet.java:141)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:404)
at org.apache.tomcat.core.Handler.service(Handler.java:286)
at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
at
org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:797)
at org.apache.tomcat.core.ContextManager.service(ContextManager.java:743)
at
org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:210)
at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:498)
at java.lang.Thread.run(Thread.java:536)
Caused by: No results were returned by the query.
at org.postgresql.jdbc2.Statement.executeQuery(Unknown Source)
at org.postgresql.jdbc2.PreparedStatement.executeQuery(Unknown Source)
at mbkennedy.pshop.servlets.PhotoServlet.processRequest(PhotoServlet.java:81)
... 12 more
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<HTML>
<HEAD><TITLE>An Error Occurred</TITLE></HEAD>
<BODY>
<H1>An Error Occurred</h1>
500 Internal Server Error
</BODY>
</HTML>
0
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<HTML>
<HEAD><TITLE>An Error Occurred</TITLE></HEAD>
<BODY>
<H1>An Error Occurred</h1>
500 Internal Server Error
</BODY>
</HTML>
0
<HTML>
<HEAD><TITLE>An Error Occurred</TITLE></HEAD>
<BODY>
<H1>An Error Occurred</h1>
500 Internal Server Error
</BODY>
</HTML>
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<HTML>
<HEAD><TITLE>An Error Occurred</TITLE></HEAD>
<BODY>
<H1>An Error Occurred</h1>
500 Internal Server Error
</BODY>
</HTML>
<?xml version="1.0" encoding="UTF-8" ?>
<!-- Created by mkennedy on February 13, 2002, 3:57 PM -->
<!DOCTYPE struts-config PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 1.0//EN"
"http://jakarta.apache.org/struts/dtds/struts-config_1_0.dtd";>
<struts-config>
<data-sources>
<data-source id="default" key="default">
<set-property property="driverClass" value="org.postgresql.Driver"/>
<set-property property="user" value="mkennedy"/>
<set-property property="password" value=""/>
<set-property property="url" value="jdbc:postgresql://localhost/pshop"/>
<set-property property="autoCommit" value="false"/>
<set-property property="description" value="PostgreSQL"/>
<set-property property="maxCount" value="1"/>
<set-property property="minCount" value="0"/>
</data-source>
</data-sources>
<global-forwards>
<forward name="index" path="/index.jsp"/>
</global-forwards>
</struts-config>
<?xml version="1.0" encoding="ISO-8859-1"?>
<!-- Created by mkennedy on February 13, 2002, 3:57 PM -->
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN"
"http://java.sun.com/j2ee/dtds/web-app_2_2.dtd";>
<web-app>
<!-- Action Servlet Configuration -->
<servlet>
<servlet-name>action</servlet-name>
<servlet-class>org.apache.struts.action.ActionServlet</servlet-class>
<init-param>
<param-name>application</param-name>
<param-value>mbkennedy.pshop.ApplicationResources</param-value>
</init-param>
<init-param>
<param-name>config</param-name>
<param-value>/WEB-INF/struts-config.xml</param-value>
</init-param>
<init-param>
<param-name>debug</param-name>
<param-value>2</param-value>
</init-param>
<init-param>
<param-name>detail</param-name>
<param-value>2</param-value>
</init-param>
<init-param>
<param-name>validate</param-name>
<param-value>true</param-value>
</init-param>
<load-on-startup>2</load-on-startup>
</servlet>
<servlet>
<servlet-name>photo</servlet-name>
<servlet-class>mbkennedy.pshop.servlets.PhotoServlet</servlet-class>
<init-param>
<param-name>bufferSize</param-name>
<param-value>8192</param-value>
</init-param>
</servlet>
<!-- Action Servlet Mapping -->
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>photo</servlet-name>
<url-pattern>/servlets/photo</url-pattern>
</servlet-mapping>
<!-- The Welcome File List -->
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<!-- Application Tag Library Descriptor -->
<taglib>
<taglib-uri>/tags/application.tld</taglib-uri>
<taglib-location>/WEB-INF/tld/appilcation/application.tld</taglib-location>
</taglib>
<!-- Struts Tag Library Descriptors -->
<taglib>
<taglib-uri>/tags/struts.tld</taglib-uri>
<taglib-location>/WEB-INF/tld/struts/struts.tld</taglib-location>
</taglib>
<taglib>
<taglib-uri>/tags/struts-bean.tld</taglib-uri>
<taglib-location>/WEB-INF/tld/struts/struts-bean.tld</taglib-location>
</taglib>
<taglib>
<taglib-uri>/tags/struts-form.tld</taglib-uri>
<taglib-location>/WEB-INF/tld/struts/struts-form.tld</taglib-location>
</taglib>
<taglib>
<taglib-uri>/tags/struts-logic.tld</taglib-uri>
<taglib-location>/WEB-INF/tld/struts/struts-logic.tld</taglib-location>
</taglib>
<taglib>
<taglib-uri>/tags/struts-html.tld</taglib-uri>
<taglib-location>/WEB-INF/tld/struts/struts-html.tld</taglib-location>
</taglib>
<taglib>
<taglib-uri>/tags/struts-template.tld</taglib-uri>
<taglib-location>/WEB-INF/tld/struts/struts-template.tld</taglib-location>
</taglib>
<!-- DBTags Tag Library Descriptor -->
<taglib>
<taglib-uri>/tags/dbtags.tld</taglib-uri>
<taglib-location>/WEB-INF/tld/dbtags.tld</taglib-location>
</taglib>
</web-app>
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