Servlets and threads
I know that the instance variables of a servlet are not thread safe, but if a HttpServletRequest creates a new thread and one is creating objects of javax.xml.parsers.DocumentBuilderFactory type (which are not thread safe) should one use synchronization? Or as I'm assuming and have read in forums.java.sun.com, that since a servlet request creates a new thread, the objects are created in a doPost, and per the javadoc "the application can have one instance of the DocumentBuilderFactory per thread" that synchronization is only a unnecessary overhead?
So essentially unthread safe classes can be unsynchronized because a servlet request runs in it's own thread, creating the object....
OK, this is final. I wrote a test servlet since I managed to confuse myself.
What I wrote in my previous post is not true. The servlet engine can reuse the same servlet instance in multiple threads, so it is NOT safe to create a DocumentBuilderFactory as an instance variable without any synchronization/locking mechanisms.
You CAN use it if you synchronize creation of DocumentBuilderFactory object and then each call for creating the DocumentBuilder itself. However, depending on how long it takes, that might make other servlets wait for access to DocumentBuilderFactory. Your servlet container might (but does not have to) create additional instances of your servlet class, but I don't think that's guaranteed.
Hope this helps & sorry for the confusion,
Mark
Similar Messages
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Problem exchanging values between a Servlet and Thread???
Hi Everybody,
I have got a problem exchanging values between a Servlet and a Thread...
The actual thing will go like this
I take a request from JSP which is served by a servlet..
A thread is invoked in the servlets into which the parameter values taken from JSP page is sent...
In between the thread needs to be suspended for a moment, relieve the control back to the servlet and then come back with the new values modified in the servlet...
How is this achieved?
Please give ur suggestions regarding this...
Thanks in advanceI really have no clue how you can use URLConnection to do that!
Could you please explain in the following scenario how it can help me as an alternative solution to the following:
Non-Servlet A continously running & saving to some prop regularly
--> servlet B reads prop file regularly --> display continously on a jsp file
I wish I could do a servlet A --> servlet B-- > display jsp scenario but I do not know how to have servlet A continously running while keep the servlet B interacting with the jsp. -
URGENT - JBO-33001 with servlet and Thread
Hi!
I'm working with BC4J, oracle AS10g, and Jdev 10g.
I make a class that uses bc4j entity objects. It works all fine when I run this class as standalone or in a servlet, but when I run that in a thread called by a servlet, it return this error:
oracle.jbo.JboException: Cannot find the configuration file mypackage1\common\bc4j.xcfg in the classpath.
at oracle.jbo.client.Configuration.loadFromClassPath(Configuration.java:358)
at oracle.jbo.common.ampool.PoolMgr.createPool(PoolMgr.java:281)
at oracle.jbo.common.ampool.PoolMgr.findPool(PoolMgr.java:482)
at oracle.jbo.common.ampool.ContextPoolManager.findPool(ContextPoolManager.java:165)
at oracle.jbo.client.Configuration.createRootApplicationModule(Configuration.java:1457)
at oracle.jbo.client.Configuration.createRootApplicationModule(Configuration.java:1435)
I've made a jar package with bc4j components, and it is present in the lib dir of the AS.
Some ideas?
ThanksHave the BC4J runtime libraries been installed in the Oracle application server?
Refer
Re: "bc4j.xcfg" file not in classpath (and not in JAR file) -
Using database connection in a servlet and get errors after 8 hours
Hey,
I'm running a poker script using applet/servlets and it works great. But for some reason about about 8 hours that database layer stops working. At first I thought it was the connections to mySQL that were timing out (because im using connection pooling) but after turning pooling off (I now create the connection each time) I'm still seeing that same error (I can create a connection but when I do an action ex. like a select statment I get an error). What i'm wondering could it be that the driver I load with Class.forName() some how unloads it's self after x amount of time not being used? Not sure if that is it but if anyone could give me some insight that would be great. The Error i recieve is below:
INFO: Database Event:DatabaseController: Error executing database query.
ERROR: Communications link failure due to underlying exception:
** BEGIN NESTED EXCEPTION **
java.net.SocketException
MESSAGE: Software caused connection abort: recv failed
STACKTRACE:
java.net.SocketException: Software caused connection abort: recv failed
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.read(Unknown Source)
at com.mysql.jdbc.util.ReadAheadInputStream.fill(ReadAheadInputStream.java:104)
at com.mysql.jdbc.util.ReadAheadInputStream.readFromUnderlyingStreamIfNecessary(ReadAheadInputStream.java:144)
at com.mysql.jdbc.util.ReadAheadInputStream.read(ReadAheadInputStream.java:172)
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:1839)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2288)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2784)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1531)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1622)
at com.mysql.jdbc.Connection.execSQL(Connection.java:2370)
at com.mysql.jdbc.Connection.execSQL(Connection.java:2297)
at com.mysql.jdbc.Statement.executeQuery(Statement.java:1183)
at com.softnet.database.DatabaseController.executeDatabaseQuery(DatabaseController.java:190)
at com.softnet.games.GameServer.validateUser(GameServer.java:438)
at com.softnet.games.GameServer.handleData(GameServer.java:113)
at com.softnet.network.HttpConnectionThread.run(HttpServletListener.java:191)
** END NESTED EXCEPTION **
I know the query is good because it works all other times just not after about 8 hours.
--Z3r0CooLHey,
Thanks for the responces. For the connection pooling I would open 5 connections and keep them open. So i though maybe after 8 hours after not being used they would timeout. Thats why i turned off conection pooling and create a new connection each time. Anyways i'll post the code below incase i made a mistake somewhere.
package com.softnet.database;
/************************ DatabaseControler **************************/
import java.sql.*;
import java.util.*;
import com.softnet.database.DatabaseConnectionPool;
import com.softnet.database.DatabaseSettings;
public class DatabaseController
implements DatabaseListener
//Used to make sure the database driver is loaded
private boolean databaseDriverState = false;
//Used to store a database connection
private Connection databaseConnection = null;
//If to user connection pooling or not
private boolean useConnectionPooling = false;
//Used to hold the connection pool varible
private DatabaseConnectionPool connectionPool = null;
//Used to store database settings
private DatabaseSettings databaseSettings;
//Used to hold the DatabaseController listeners
private List databaseControllerListeners = new ArrayList();
//min number of connections for connection pool
private int minNumberOfConnections = 1;
//max number of connections for connection pool -1 is unlimited
private int maxNumberOfConnections = -1;
//DatabaseController Constructors
public DatabaseController(DatabaseSettings databaseSettings)
this.databaseSettings = databaseSettings;
databaseDriverState = loadDatabaseDriver(databaseSettings.getDatabaseDriver());
public DatabaseController(DatabaseSettings databaseSettings, boolean useConnectionPooling, int minNumberOfConnections, int maxNumberOfConnections)
this.databaseSettings = databaseSettings;
this.useConnectionPooling = useConnectionPooling;
this.minNumberOfConnections = minNumberOfConnections;
this.maxNumberOfConnections = maxNumberOfConnections;
if(useConnectionPooling == true)
connectionPool = new DatabaseConnectionPool(databaseSettings, minNumberOfConnections, maxNumberOfConnections);
connectionPool.addDatabaseListener(this);
else
databaseDriverState = loadDatabaseDriver(databaseSettings.getDatabaseDriver());
public DatabaseController() {}
//Database Settings Get/Set
public DatabaseSettings getDatabaseSettings()
return databaseSettings;
public void setDatabaseSettings(DatabaseSettings databaseSettings)
this.databaseSettings = databaseSettings;
//Connection Pooling Get/Set
public boolean getConnectionPooling()
return useConnectionPooling;
public void setConnectionPooling(boolean useConnectionPooling, int minNumberOfConnections, int maxNumberOfConnections)
this.useConnectionPooling = useConnectionPooling;
this.minNumberOfConnections = minNumberOfConnections;
this.maxNumberOfConnections = maxNumberOfConnections;
if(useConnectionPooling == true)
if(connectionPool == null)
connectionPool = new DatabaseConnectionPool(databaseSettings, minNumberOfConnections, maxNumberOfConnections);
connectionPool.addDatabaseListener(this);
else
if(connectionPool != null)
connectionPool.destroyConnections();
connectionPool.removeDatabaseListener(this);
connectionPool = null;
//Return if there connected
public boolean isConnected()
boolean isConnected;
if(databaseConnection != null)
isConnected = true;
else
isConnected = false;
return isConnected;
//Used to connect to database or get a connection for the connection pool
public void connect()
if(databaseDriverState == false)
databaseDriverState = loadDatabaseDriver(databaseSettings.getDatabaseDriver());
//If we dont have a current connection, make one
if(databaseConnection == null && databaseDriverState == true)
if(useConnectionPooling == false)
try
databaseConnection = DriverManager.getConnection(databaseSettings.getDatabaseURL(), databaseSettings.getUserName(), databaseSettings.getUserPassword());
catch (SQLException sqle)
//Raise event
raiseDatabaseEvent("DatabaseController: Error connecting to database. \nERROR: " + sqle.getMessage());
databaseConnection = null;
else
databaseConnection = connectionPool.getConnection();
//Used to disconnect from the database or give back the connection to the connection pool
public void disconnect()
if(databaseConnection != null)
if(useConnectionPooling == false)
try
//Close DB Connection
databaseConnection.close();
catch(SQLException ignore) {}
finally
databaseConnection = null;
else
connectionPool.returnConnection(databaseConnection);
databaseConnection = null;
public ResultSet executeDatabaseQuery(String sSQL)
ResultSet databaseResult = null;
if(databaseConnection != null)
try
Statement databaseStatement = databaseConnection.createStatement();
databaseResult = databaseStatement.executeQuery(sSQL);
catch(SQLException sqle)
//Raise event
raiseDatabaseEvent("DatabaseController: Error executing database query.\nSQL: " + sSQL + "\nERROR: " + sqle.getMessage());
return databaseResult;
public int executeDatabaseUpdate(String sSQL)
int rowsAffected = -1;
if(databaseConnection != null)
try
Statement databaseStatement = databaseConnection.createStatement();
rowsAffected = databaseStatement.executeUpdate(sSQL);
catch(SQLException sqle)
//Raise event
raiseDatabaseEvent("DatabaseController: Error executing database update.\nSQL: " + sSQL + "\nERROR: " + sqle.getMessage());
return rowsAffected;
//Used to load the Database Driver
private boolean loadDatabaseDriver(String databaseDriver)
boolean driverLoaded;
if(databaseDriver.equals("") == false)
try
//Load Database Driver
Class.forName(databaseDriver).newInstance();
driverLoaded = true;
catch (Exception e)
//Raise event
raiseDatabaseEvent("DatabaseController: Error loading database driver. \nERROR: " + e.getMessage());
driverLoaded = false;
else
driverLoaded = false;
return driverLoaded;
//Wrap the DatabaseConnectionPool Error to the DatabaseController
public void databaseEventOccurred(DatabaseEvent de)
raiseDatabaseEvent(de.getErrorMessage());
//Event Handling Code
//Used to add database listeners (Its sync'd so you can change the listeners when firing an event)
public synchronized void addDatabaseListener(DatabaseListener databaseControllerListener)
databaseControllerListeners.add(databaseControllerListener);
//Used to remove a listener from the list (Its sync'd so you can change the listeners when firing an event)
public synchronized void removeDatabaseListener(DatabaseListener databaseControllerListener)
databaseControllerListeners.remove(databaseControllerListener);
//Used to send the raise event to the listeners
private synchronized void raiseDatabaseEvent(String databaseError)
DatabaseEvent databaseEvent = new DatabaseEvent(this, databaseError);
Iterator listeners = databaseControllerListeners.iterator();
while(listeners.hasNext())
DatabaseListener listener = (DatabaseListener) listeners.next();
listener.databaseEventOccurred(databaseEvent);
/********************* DatabaseConnectionPool **************/
package com.softnet.database;
import java.io.*;
import java.sql.*;
import java.util.*;
import com.softnet.database.*;
import com.softnet.database.DatabaseSettings;
public class DatabaseConnectionPool
//min number of connections
private int minNumberOfConnections = 1;
//max number of connections -1 is unlimited
private int maxNumberOfConnections = -1;
//Store the connections
protected Hashtable databaseConnections = null;
//Database Info
protected DatabaseSettings databaseSettings;
//to hold Driver state
private boolean databaseDriverState = false;
//To hold connection checker
private DatabaseConnectionCheck connectionChecker = null;
//Used to hold the DatabaseConnectionPool listeners
private List databaseConnectionPoolListeners = new ArrayList();
public DatabaseConnectionPool(DatabaseSettings databaseSettings, int minNumberOfConnections, int maxNumberOfConnections)
this.databaseSettings = databaseSettings;
this.minNumberOfConnections = minNumberOfConnections;
this.maxNumberOfConnections = maxNumberOfConnections;
//Load Driver
databaseDriverState = loadDatabaseDriver(databaseSettings.getDatabaseDriver());
//Create connection
createConnections();
public DatabaseConnectionPool(int minNumberOfConnections, int maxNumberOfConnections)
this.minNumberOfConnections = minNumberOfConnections;
this.maxNumberOfConnections = maxNumberOfConnections;
//Database Settings Get/Set
public DatabaseSettings getDatabaseSettings()
return databaseSettings;
public void setDatabaseSettings(DatabaseSettings databaseSettings)
this.databaseSettings = databaseSettings;
//Driver State Get
public boolean getDatabaseDriverState()
return databaseDriverState;
public void createConnections()
if(databaseDriverState == false)
databaseDriverState = loadDatabaseDriver(databaseSettings.getDatabaseDriver());
//Create all connections and load the minimum in the Hashtable
if(databaseConnections == null)
if(databaseDriverState == true && minNumberOfConnections != 0)
databaseConnections = new Hashtable();
for(int i = 0; i < minNumberOfConnections; i++)
try
databaseConnections.put(DriverManager.getConnection(databaseSettings.getDatabaseURL(), databaseSettings.getUserName(), databaseSettings.getUserPassword()), Boolean.FALSE);
catch(SQLException sqle)
//Problem break loop and destroy any connections
destroyConnections();
//Raise event
raiseDatabaseEvent("DatabaseConnectionPool: Error creating database connections. \nERROR: " + sqle.getMessage());
break;
//If no connection check exists create one
if(connectionChecker == null)
connectionChecker = new DatabaseConnectionCheck(this);
connectionChecker.start();
public Connection getConnection()
Connection connection = null;
boolean errorWithConnection = false;
Enumeration connections = databaseConnections.keys();
synchronized (databaseConnections)
while(connections.hasMoreElements())
errorWithConnection = false;
connection = (Connection) connections.nextElement();
Boolean state = (Boolean) databaseConnections.get(connection);
//If connection is not used, use it.
if(state == Boolean.FALSE)
try
connection.setAutoCommit(true);
catch(SQLException e)
//Problem with connection remove connection and replace it
databaseConnections.remove(connection);
try
connection = DriverManager.getConnection(databaseSettings.getDatabaseURL(), databaseSettings.getUserName(), databaseSettings.getUserPassword());
catch(SQLException sqle)
errorWithConnection = true;
if(errorWithConnection == false)
// Update the Hashtable to show this one's taken
databaseConnections.put(connection, Boolean.TRUE);
// Return the connection
return connection;
//All connections being used check to max to see if we can make a new one
if(maxNumberOfConnections == -1 || maxNumberOfConnections > databaseConnections.size())
try
connection = DriverManager.getConnection(databaseSettings.getDatabaseURL(), databaseSettings.getUserName(), databaseSettings.getUserPassword());
catch(SQLException sqle)
errorWithConnection = true;
if(errorWithConnection == false)
databaseConnections.put(connection, Boolean.TRUE);
return connection;
//If not connections free and max connections reached wait for a free connection
return getConnection();
public void returnConnection(Connection connection)
boolean errorWithConnection = false;
//Make sure connection still works
try
connection.setAutoCommit(true);
catch(SQLException e)
//Problem with connection remove connection and replace it
databaseConnections.remove(connection);
try
connection = DriverManager.getConnection(databaseSettings.getDatabaseURL(), databaseSettings.getUserName(), databaseSettings.getUserPassword());
catch(SQLException sqle)
errorWithConnection = true;
if(errorWithConnection == false)
databaseConnections.put(connection, Boolean.FALSE);
public void destroyConnections()
Connection connection = null;
if(databaseConnections != null)
//Close all connections
Enumeration connections = databaseConnections.keys();
while (connections.hasMoreElements())
connection = (Connection) connections.nextElement();
try
connection.close();
catch(SQLException ignore) {}
//Free up hashtable
databaseConnections = null;
private boolean loadDatabaseDriver(String databaseDriver)
boolean driverLoaded;
if(databaseDriver.equals("") == false)
try
//Load Database Driver
Class.forName(databaseDriver);
driverLoaded = true;
catch (ClassNotFoundException cnfe)
//Raise event
raiseDatabaseEvent("DatabaseController: Error loading database driver. \nERROR: " + cnfe.getMessage());
driverLoaded = false;
else
driverLoaded = false;
return driverLoaded;
//Event Handling Code
//Used to add database listeners (Its sync'd so you can change the listeners when firing an event)
public synchronized void addDatabaseListener(DatabaseListener databaseConnectionPoolListener)
databaseConnectionPoolListeners.add(databaseConnectionPoolListener);
//Used to remove a listener from the list (Its sync'd so you can change the listeners when firing an event)
public synchronized void removeDatabaseListener(DatabaseListener databaseConnectionPoolListener)
databaseConnectionPoolListeners.remove(databaseConnectionPoolListener);
//Used to send the raise event to the listeners
private synchronized void raiseDatabaseEvent(String databaseError)
DatabaseEvent databaseEvent = new DatabaseEvent(this, databaseError);
Iterator listeners = databaseConnectionPoolListeners.iterator();
while(listeners.hasNext())
DatabaseListener listener = (DatabaseListener) listeners.next();
listener.databaseEventOccurred(databaseEvent);
class DatabaseConnectionCheck extends Thread
private DatabaseConnectionPool connectionPool;
DatabaseConnectionCheck(DatabaseConnectionPool connectionPool)
this.connectionPool = connectionPool;
public void run()
try
while(true)
//check threads every 30 seconds
this.sleep(300000);
if(connectionPool.databaseConnections != null)
Connection connection = null;
Enumeration connections = connectionPool.databaseConnections.keys();
synchronized (connectionPool.databaseConnections)
while(connections.hasMoreElements())
connection = (Connection) connections.nextElement();
Boolean state = (Boolean) connectionPool.databaseConnections.get(connection);
//If connection is not used, use it.
if(state == Boolean.FALSE)
try
connection.setAutoCommit(true);
catch(SQLException e)
//Problem with connection remove connection and replace it
connectionPool.databaseConnections.remove(connection);
try
connection = DriverManager.getConnection(connectionPool.databaseSettings.getDatabaseURL(), connectionPool.databaseSettings.getUserName(), connectionPool.databaseSettings.getUserPassword());
catch(SQLException sqle)
connection = null;
// Update the Hashtable with new connection if its not null
if(connection != null)
connectionPool.databaseConnections.put(connection, Boolean.FALSE);
catch(InterruptedException ignored) {}
Basicly the why it works is the connection pool hold the database connections. When the user needs a connection they use the database controller to request a connection (By create a instance and called the connect() method) and the connection is either created or grabed from the connection pool. After the user is done with the connection they call the disconnect() method which closes the connection or returns it to the connection pool.
--Z3r0CooL -
Creating FOrums with Servlet and JSP
Hi everyone,
Is there a good resource that explains how to build a forum using servlets and JSP technology?
Regards,
Basil Mahdiplease let me know here if you find any useful resources...I am in the process of writing my own searchable threaded forum for my company with JSP's/servlets. It's a very slow process at the moment though...if I ever finish it, I'll gladly share it.
-
Differences between WL or Netscape for Servlets and JSP's
What are the advantages / disadvantages of running Servlets under WL,
vs. say, running them in Netscape's servlet engine? Assuming EJB
container is run separately, either one of these could make calls to the
WL EJB server, so perhaps it would be simpler and faster to run servlets
and JSP's under Netscape, and have them call via t3 into a weblogic
server for EJB's?
Thoughts
david
David Michaels <[email protected]>
Director of Technology
ShockMarket Corporation (650) 330-4665
[david.vcf]
David,
One of the major reasons to run your servlets on Weblogic is that we have an
optimization that allows us to pass by reference objects when calling from
servlets to EJB. This makes things much faster.
A number of our customers, in addition, have seen performance problems when
using other servlet engines. It just seems to cause problems due to their
threading models etc.
Finally, our servlet engine is by far the most mature and robust on the
market today. Our JSP implementation is also the best in terms of
performance.
Thanks,
Michael
Michael Girdley
WLS Product Manager
David Michaels <[email protected]> wrote in message
news:[email protected]..
> What are the advantages / disadvantages of running Servlets under WL,
> vs. say, running them in Netscape's servlet engine? Assuming EJB
> container is run separately, either one of these could make calls to the
> WL EJB server, so perhaps it would be simpler and faster to run servlets
> and JSP's under Netscape, and have them call via t3 into a weblogic
> server for EJB's?
>
> Thoughts
>
> david
>
> --
> David Michaels <[email protected]>
> Director of Technology
> ShockMarket Corporation (650) 330-4665
>
>
-
I am new to the servlet and JSP technology.It is said that "Servlets and CGI differ mainly in Process and Thread.CGI used processes and Servlet technology uses Threads".I would like to know what exacly is the meaning of a process and a thread.How do we say that a process uses higher resources and hence a higher resource and memory overhead.
What do we exactly mean by thread and how r they using less resources?When we say Thread t=new Thread(); what exactly is happening inside?A thread runs with in the context of the JVM process.
http://java.sun.com/docs/books/tutorial/essential/threads/definition.html
A process is the running of an executable. A cgi can be a C .exe file or a perl script run under perl.exe.
The thread is faster because the jvm process has been loaded into memory and initialized. For each cgi call the operating system has to load the code into memeory and intialize all the variables and resources.
http://c2.com/cgi/wiki?CgiVsServlet
http://www.disc.com/jdbcserv.html -
Servlet and Object Serialization
Hi,
I am developing a routing server in Java
2 Instances of the same server will be running in 2 different data centers.
The servers have a Jetty server embedded with a Servlet inside.
Server 1 will use a GET method to talk to the Server 2 -> Servlet which will write the state of an object back which will read by Server 1 and reconstruct the object back.
Do you find any issues in Object Serialization/DeSerialization in the Servlet.
What are the factors that I need to consider in this case?
Regards,
JanaMake sure that your servlet handles the transaction in the same thread that doPost() or doGet() is called in.
I ended up porting some old ServerSocket based code to a servlet, and was handing off the request and response objects to a handler thread on the server side. I ended up with a ton of intermittent errors like this.
Once I started handling the transactions in the same thread things worked heartbreakingly well. -
Servlet and Actions - Apache Struts !
Hi,
i defined an ActionServlet in the web.xml and some "Actions" in the struts-config.xml.
If all the requests are managed by the servlet defined in the web.xml, in case i had a lot of requests would it be better defined more ActionServlet in the web.xml which refers to different struts-config.xml ?
I think that having more servlet is much better to manage the load of the entire application.
Any suggestions ?
Cheers.
StefanoNo need creating more than one ActionServlet : Servlets are Threads so each request made by a client is handled by a different Thread!
-
Problem for getting the real path using one servlet and one jsp page
I have one tomcat machine and several virtual domains. Eahc virtual domain has one realpath in the disc.
I am using one servlet and one jsp page for using this servlet.
my purpose is to load, using the servlet , the real path for the domains (eahc domain has its path).
for this i make this:
the servlet code is this:
package utils.ticker;
import java.io.*;
import java.io.File;
import java.io.IOException;
import java.net.*;
import java.util.*;
import java.text.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.http.HttpServlet;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class Edicion extends HttpServlet{
public Edicion() {
public String cc(){
ServletContext myContext= getServletContext();
String abspath = myContext.getRealPath("/");
//here i want to return the real path
return abspath;
public static void main(String args[]){
and the jsp page is:
<%@ page import="utils.ticker.*" %>
<jsp:useBean id="tick" class="utils.ticker.Edicion" scope="session"/>
<html><head><body>
<%
tick.cc();
%>
</body></head></html>
But this produces one error, NullPointerException and dont shows me the real path.
Can anyone help me?
thanksi have put this into one sevlet:
package utils.ticker;
import javax.servlet.ServletContext;
public class Edicion{
private ServletContext myContext;
public Edicion(ServletContext myContext) {
this.myContext = myContext;
public String getCC(){
return myContext.getRealPath("/");
and in the jsp page this:
<%@ page contentType="text/html; charset=iso-8859-1" language="java" import="java.sql.*"%>
<%@ page import="utils.ticker.*" %>
<jsp:useBean id="tick" class="utils.ticker.Edicion" scope="session"/>
<html><head><body>
<%=tick.getCC()%>
</body></head></html>
but appear this error in the tomcat.
Can you, please, help me. i am trying to solve this during one week and i am desesperate.
Thanks.
ERROR:
HTTP Status 500 -
type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: class utils.ticker.Edicion : java.lang.InstantiationException: utils.ticker.Edicion
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:248)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:295)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:260)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2415)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:170)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:223)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:432)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:386)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:534)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:530)
at java.lang.Thread.run(Thread.java:536)
root cause
javax.servlet.ServletException: class utils.ticker.Edicion : java.lang.InstantiationException: utils.ticker.Edicion
at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:533)
at org.apache.jsp.pruebas_jsp._jspService(pruebas_jsp.java:72)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:137)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:204)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:295)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:260)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2415)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:170)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:223)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:432)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:386)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:534)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:530)
at java.lang.Thread.run(Thread.java:536)
Apache Tomcat/4.1.18 -
Servlets and multiple JDBC connections...
Hi Guru's
I want to perform multiple JDBC queries simultaneously from my servlet. Let's say I have a connection pool containing JDBC connections. Now what I want to do is to use each of this connections simultaneously to perform queries in parallel.
What is the best way to do this??? create multiple threads, one for each query, and then collate results when all threads are finished???
Has anyone does this before or know of any links or samples which I can look at??
your help much appreciated...
Many ThanksThanks but further questions....
But take care:
multithreading might only work parallel if there are
multiple processors - otherwise the thread fragments
will be processed one after the other until they are
finished.I agree. My server has multiple processors hence multi-threading.
Why do you need to perform the queries
simultaneously?
wouldn't it work too when you perform the queries one
after the other?To speed up performance. Sequential processing is too slow at the moment.
Hope you don't try doing so inside one single
database...yes inside a single databse.
Do you have any links to sample example etc..??? Importantly are you aware of any issues when one does this type of multi-threading from servlet. i.e does it clash with servlet's threading model etc...
I am aware of how servlets multithread requests and am quite familiar with them. Just wanted some examples on multithreading JDBC connections from servlets and how I can wait for all threads to finish before collecting results....also wanted to make sure that there are no other issues....
further help will be much appreciated..... -
Sharing config with Servlet and Web Services
Hi,
I am building a Servlet wrapper and a jaxrpc wrapper for my application, so that my client can invoke either servlet or web services to access my application.
my main application library is at WEB-INF/lib and both the servlet and
webservices are in WEB-INF/classes.
I am trying to make them sharing the same configuration file web.xml so that common attributes such as log file location can be read. I know Servlet can read the context and parameters but how to make my web services app to read it, since the web services are not servlet itself but it is invoked by the JAXRPC servlet????
ThanksThe early post may answer your question:
http://forum.java.sun.com/thread.jsp?forum=331&thread=266102 -
Servlets and java.util.concurrent
Hey --
I know one is not supposed to spawn their own threads from Servlets and EJBs, but is it also 'bad form' to use Callables from a Servlet or EJB? If not can something similar be done safely?
I need to be able to (a) submit a file to be processed (b) give the user back a 'got it, will work on it' response, (c) let the user see the status of his 'job' and (4) open the results when complete.
The file processing would be running outside of the normal send request/return response path which is, of course, a synchronous process. I don't see a way, other than spawning a thread in that servlet (or another servlet which manages the 'jobs') to provide for 'long running processes.'
Thanks for any insight.
- Z -
Message was edited by:
zelmakHey --
I know one is not supposed to spawn their own threads from Servlets and EJBs, but is it also 'bad form' to use Callables from a Servlet or EJB? If not can something similar be done safely?
I need to be able to (a) submit a file to be processed (b) give the user back a 'got it, will work on it' response, (c) let the user see the status of his 'job' and (4) open the results when complete.
The file processing would be running outside of the normal send request/return response path which is, of course, a synchronous process. I don't see a way, other than spawning a thread in that servlet (or another servlet which manages the 'jobs') to provide for 'long running processes.'
Thanks for any insight.
- Z -
Message was edited by:
zelmak -
Under normal conditions a web-container creates only one instance of servlet.Now the case is I am creating instance of a class in the servlet.So for every request to the servlet does an instance of the class is created?
If you make the instance in a service method (service(), doGet(), doPost() etc...) then yes, each request will create a new instance.
If you create the instance anyplace else, no they will share it.
If you hold the reference to the class in the servlet class level as opposed to storing it in the method which creates and uses it, then you can run into problems as well, since there will be only one reference for all requests.
So generally speaking in Servlets (and in any application you need to worry about thread safety:
This is bad. One object will be used by all requests:
public class BadServlet ... {
Object myObject = new Object();
public void doGet(...) ... {
do something with myObject;
}This is bad. A new instance is made for each request, but only one reference. So one request will end up using another's instance:
public class BadServlet ... {
Object myObject;
public void doGet(...)... {
myObject = new Object();
do something with myObject;
}This is how you would do it in a thread safe manner:
public class GoodServlet ...{
public void doGet(...)... {
Object myObject = new Object();
//Another method in same class needs a reference? Pass it as a parameter
someOtherMethod(myObject);
//Some other servlet needs access? Store it in Request scope
request.setAttribute("myObject", myObject);
//Some other request needs to access it? Put it in the session scope
HttpSession session = request.getSession();
session.setAttribute("myObject", myObject);
private void doSomething(Object myObject) ... {
do something with myObject
} -
Help needed on Servlets and JSTL
Hi
I am using tomcat 5.5 and JDK 1.5. What are the softwares I have to download for compiling servlets and creating JSTL ?. Help needed.
Thanks
IndyaRajaI tried compling servlet, but it is raising error
that coul not find package javax.servletWhat I did not mention... you need to add those JARs in the Classpath explicitly. You will find them in %TOMCAT_HOME%\common\lib. You atleast need to add servlet-api.jar to your Classpath. :)
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