We Keep Coding

Why path on server throw NullPonterException?

I have a problem with the path to the file. Locally (Windows), the tests pass, but when I upload it to the server(Linux), I have:
NullPointerException: Cannot get property 'text' on null object
Sample code:
public final String MAIN = "dir1/dir2/dir3/"
public final String CAT_1 = MAIN + "subdirectory/"
somewhere in the method ...
def object = Utils.class.getClassLoader().getResource(CAT_1 + "file.xml").text
unmarshaller.unmarshal(new StringSource(object), SomeClass.class).value

Why path on server throw NullPonterException?
Utils.class.getClassLoader().getResource(CAT_1 + "file.xml").text will throw a NullPointerException if CAT_1 + "file.xml" can't be loaded because getResource is going to return null.
Apparently that resource is not available at the path you are expecting it to be available at.

Can't use "Handler" approach to adding a URLStreamHandler in AWS Lambda

I'm currently trying to add a URLStreamHandler so I can handle URLs with custom protocols. This works fine when run locally. When deployed to AWS Lambda I get:
java.net.MalformedURLException: unknown protocol: baas
I'm following the "Handler" approach to registering the URLStreamHandler.
I even went as far as copying the code from URL.getURLStreamHandler(String) and added logging into my own code that is run by Lambda:
(Note: this is from the Java 8 source - I realise now that this might not be representative because AWS Lambda uses a Java 11 runtime).
URLStreamHandler handler = null;
String packagePrefixList = null;
packagePrefixList
= java.security.AccessController.doPrivileged(
new sun.security.action.GetPropertyAction(
"java.protocol.handler.pkgs",""));
if (packagePrefixList != "") {
packagePrefixList += "|";
}
// REMIND: decide whether to allow the "null" class prefix
// or not.
packagePrefixList += "sun.net.www.protocol";
LOG.debug("packagePrefixList: " + packagePrefixList);
StringTokenizer packagePrefixIter =
new StringTokenizer(packagePrefixList, "|");
while (handler == null &&
packagePrefixIter.hasMoreTokens()) {
String packagePrefix =
packagePrefixIter.nextToken().trim();
try {
String clsName = packagePrefix + "." + "baas" +
".Handler";
Class<?> cls = null;
LOG.debug("Try " + clsName);
try {
cls = Class.forName(clsName);
} catch (ClassNotFoundException e) {
ClassLoader cl = ClassLoader.getSystemClassLoader();
if (cl != null) {
cls = cl.loadClass(clsName);
}
}
if (cls != null) {
LOG.debug("Instantiate " + clsName);
handler =
(URLStreamHandler)cls.newInstance();
}
} catch (Exception e) {
// any number of exceptions can get thrown here
LOG.debug(e);
}
}
This prints (in Cloudwatch logs):
packagePrefixList: com.elsten.bliss|sun.net.www.protocol (BaasDriver.java:94, thread main)
Try com.elsten.bliss.baas.Handler (BaasDriver.java:108, thread main)
Instantiate com.elsten.bliss.baas.Handler (BaasDriver.java:118, thread main)
com.elsten.bliss.baas.Handler constructor (Handler.java:55, thread main)
So, when run from my own code, in Lambda, it works.
However, the very next line of logging:
java.lang.IllegalArgumentException: URL is malformed: baas://folder: java.lang.RuntimeException
java.lang.RuntimeException: java.lang.IllegalArgumentException: URL is malformed: baas://folder
...
Caused by: java.net.MalformedURLException: unknown protocol: baas
at java.base/java.net.URL.<init>(Unknown Source)
at java.base/java.net.URL.<init>(Unknown Source)
at java.base/java.net.URL.<init>(Unknown Source)
So it seems odd the same code is failing when run in URL. The main difference I can think of is the parent classloader used to load URL and my code are different, and so there's some sort of class loading issue.
The SPI approach can't be used because Lambda doesn't extract META-INF folders!

Initially I thought the old URL.setURLStreamHandlerFactory(URLStreamHandlerFactory) approach was to be avoided, but it turns out this has been improved in recent Java versions, and so I have fallen back to that.
Specifically, a default fallback URLStreamHandlerFactory which is capable of handling streams to http, https, file et al is used as a fallback if the custom one provided cannot handle a stream.
This is a workaround though - it would be interesting to know why the class cannot be loaded.

Loading versions of the same class (Java)

I am writing a program to allow my students to engage in a rudimentary AI game (similar to something IBM did years ago). The idea is pretty simple. Everyone has a project with the game jar, and their AI class MyAI.java (which implements AbstractAI). The structure is all working, they can write code into their AI class, and submit it to a common folder. The structure of the folder once a few students have submitted is:
school/stud1/MyAI.class
school/stud2/MyAI.class
I have also written code that I thought (in retrospect quite naively) would load and instantiate all of the classes into an ArrayList. The problem, is that I end up with an ArrayList of x instances of the current class.
I've found some similar questions, but the accepted answers did not work in this instance.
Some of the Loader class (not prettied up, it was just a proof of concept) is included below:
/**
* Load a single ai from a given location
* #param location The path where the ai is: example: c:\\tourney
* #param className The complete class: "org.mrd.Tournament.MyAI"
* #return The instance of AbstractAI loaded
*/
public static AbstractAI loadAI(String location, String className){
Object o = null;
try {
o = new URLClassLoader( new URL[]{new File(location).toURI().toURL()}
).loadClass(className).newInstance();
} catch ...{
}
if (o == null) return null;
return (AbstractAI)o;
}
/**
* Load all current files in tournament folder.
*/
public static ArrayList<AbstractAI> loadCurrentTourneyFiles(){
File dirs = new File("d:\\tourney\\school");
//list of all file names
ArrayList<String> names = new ArrayList<String>(Arrays.asList(dirs.list()));
//Create an arraylist for all loaded AIs and load them.
ArrayList<AbstractAI> arar = new ArrayList();
for (String dir:names){
arar.add(loadAI(dirs.getAbsolutePath() + "\\" + dir, "org.mrd.Tournament.MyAI"));
}
return arar;
}
Most relevant threads:
Java ClassLoader: load same class twice
Java - how to load different versions of the same class?

You can try to use compilation-toolbox, the idea is that you would try to load each of student jar with the following snippet:
JavaSourceCompiler javaSourceCompiler = new JavaSourceCompilerImpl();
JavaSourceCompiler.CompilationUnit compilationUnit = javaSourceCompiler.createCompilationUnit();
compilationUnit.addClassPathEntry("ai_student1.jar");
compilationUnit.addClassPathEntry("abstract_ai.jar");
String aiProvider = "package com.ai;\n" +
" import com.ai.student.AI;\n" +
"import com.ai.AbstractAI;\n" +
" public class AIProvider {\n" +
" public AbstractAI get() {\n" +
" return new AI();\n" +
" }\n\n" +
" }";
ClassLoader classLoader = javaSourceCompiler.compile(compilationUnit);
Class aIProvider = classLoader.loadClass("com.ai.Provider");

How to get an Initial Contex from Wildfly 8

ADDED 7/23.
Many views: Not even a "that's dumb" question in response. Can anyone at least tell me why such an embarrassingly trivial question seems to have no answer anywhere.
Q:
--- Have Wildfly 8 running on local machine localhost:9990.
--- Have a Java program that need's Wildfly's IntialContext.
--- Every reference says use: "Context ctx = new InitialContext(env);"
--- Yet a week of searching turns up no set of properties that returns one.
And no example of a java program that gets one.
Does no one ever do this? Really need help
Original Msg Below
I know many people have asked how to get an Initial context from Wildfly 8. But I have yet to find a simple answer with a simple example.
Therefore, I hope someone can tell my why this doesn’t work.
I start Wildfly with standalone-full.xml
The three sections below have
A - Code summary of my test Class whose only purpose is to secure an Initial Context. (I only removed a lot of printing code that produced the next section.]
B - The Eclipse console output for a failure.
C - Cut and paste code. Just in case anyone can help me get this to work. I’d like to leave behind something the next new WF user can cut and past and run. The only difference from 1 above is that this version has all the static methods I used to format the output. NOTE: I know the comments I inserted about the less than sign sound dumb. BUT ... they are true.
A Code Summary
import java.util.Properties;
import javax.naming.CommunicationException;
import javax.naming.Context;
import javax.naming.InitialContext;
public class JmsTestGetJNDIContext {
//members
final private Properties env = new Properties() {
private static final long serialVersionUID = 1L;
{
/* These are Properties used by a standalone JavaClient to secure a WIldFly InitialContext()*/
put(Context.INITIAL_CONTEXT_FACTORY, "org.jboss.naming.remote.client.InitialContextFactory");
put(Context.PROVIDER_URL,"http-remoting://localhost:9990");
put(Context.SECURITY_PRINCIPAL,"userGLB");
put(Context.SECURITY_CREDENTIALS,"Open");
put("jboss.naming.client.ejb.context", true);
/*The above URL, ID and PW successfully open Wildfly's Admin Console*/
}
};
//constructor
private JmsTestGetJNDIContext (){
/*print "beg"*/
/*print "env"*/
try {
/*print "Requesting InitialContext"*/
Context ctx = new InitialContext(this.env);
/*print "JNDI Context: " + ctx)*/
/*print "end");
} catch (CommunicationException e) {
/* print "You forgot to start WildFly dummy!"*/
} catch (Exception e) {
/* print"caught: " + e.getClass().getName()*/
/*print e.getMessage()*/
/* "end")*/
}
static public void main (String[] args) {
/*print "beg"*/
JmsTestGetJNDIContext client = new JmsTestGetJNDIContext ();
/*print "end"*/
}
}
B - Console Output
JmsTestGetJNDIContext.main () beg
JmsTestGetJNDIContext.<init> () beg
JmsTestGetJNDIContext.<init> () These are Properties used to obtain IntialContext
Key: java.naming.provider.url
Value: http-remoting://localhost:9990
Key: java.naming.factory.initial
Value: org.jboss.naming.remote.client.InitialContextFactory
Key: jboss.naming.client.ejb.context
Value: true
Key: java.naming.security.principal
Value: userGLB
Key: java.naming.security.credentials
Value: Open
JmsTestGetJNDIContext.<init> () Requesting InitialContext
JmsTestGetJNDIContext.<init> () caught: javax.naming.NamingException
JmsTestGetJNDIContext.<init> () Failed to create remoting connection
JmsTestGetJNDIContext.<init> () end
JmsTestGetJNDIContext.main () end
Cut and Paste Code
package org.america3.gotest.xtra;
import java.util.Properties;
import javax.naming.CommunicationException;
import javax.naming.Context;
import javax.naming.InitialContext;
public class JmsTestGetJNDIContext {
//members
final private Properties env = new Properties() {
/**
* Properties used by a standalone JavaClient to secure
* a WIldFly InitialContext()*/
private static final long serialVersionUID = 1L;
{
put(Context.INITIAL_CONTEXT_FACTORY,"org.jboss.naming.remote.client.InitialContextFactory");
put(Context.PROVIDER_URL, "http-remoting://localhost:9990");
put(Context.SECURITY_PRINCIPAL, "userGLB");
put(Context.SECURITY_CREDENTIALS, "Open");
// The above URL, ID and PW successfully open Wildfly's Admin Console
put("jboss.naming.client.ejb.context", true);
}
};
//constructor
private JmsTestGetJNDIContext (){/*ignore*/String iAm = JmsTestGetJNDIContext.getIAm(" ", Thread.currentThread().getStackTrace());
P (iAm, "beg");
pProps(iAm, env);
try {
P (sp + iAm, "Requesting InitialContext");
Context ctx = new InitialContext(this.env);
P (sp + iAm, "JNDI Context: " + ctx);
P (sp + iAm, "end");
} catch (CommunicationException e) {
P (sp + iAm, "You forgot to start WildFly dummy!");
} catch (Exception e) {
P (sp + iAm, "caught: " + e.getClass().getName());
P (sp + iAm, e.getMessage());
P (iAm, "end");
}
}
static public void main (String[] args) {/*ignore*/String iAm = JmsTestGetJNDIContext.getIAm("",Thread.currentThread().getStackTrace());
P (iAm, "beg");
JmsTestGetJNDIContext client = new JmsTestGetJNDIContext ();
P (iAm , "end");
}
/*The remaining static methods are just to facilitate printing.
* They are normally in a Untility package I add to my projects.
* I put them here so this code would run for anyone.*/
static private void pProps (String leader, Properties p) {
StringBuffer sb = new StringBuffer ();
String s = JmsTestGetJNDIContext.padRight(leader, 45, ' ');
s = " " + s + "These are Properties used to obtain IntialContext"+"\n";
sb.append(s);
String skip = "";
for (Object key: p.keySet()) {
sb.append(skip + " " + JmsTestGetJNDIContext.padRight("\""
+ (String)key + "\"", 40, ' ')
+ " \"" + p.get(key) + "\"");
skip = "\n";
}
System.out.println(sb);
}
static private void P (String s, String s2) {
System.out.println(s + s2);
}
static public String getClassMethodName (StackTraceElement[] elements) {
String className = null;
for (int i = 0; i * elements.length; i++]i ) {
/* You need to type in a less than sign for the '*'
* because when I do, the editor will not show any code
* that comes after it.
* I have no idea why, but I've spent over an hour trying,
* and every time I type a less than sign all the following
* code dissappears!*/
className = elements[i].getClassName ();
if (className.startsWith ("org.america3")) {
int end = className.lastIndexOf ('.');
return className.substring (end + 1) + "." + elements[i].getMethodName ();
} else {
continue;
}
}
return "no project method found in elements beginning with org.america3" ;
}
static private String getIAm (String indent, StackTraceElement[] elements) {
StringBuffer sb = new StringBuffer ();
sb.append(JmsTestGetJNDIContext.getClassMethodName(elements));
sb.append(" ()");
return indent + JmsTestGetJNDIContext.padRight (sb.toString(), 45, ' ') ;
}
static public String padRight(String s, int width, char c){
if (s == null) return "Null String";
if(s.length() ** width){
/* You need to type in a greater than or equal sign for
* the '**'see above.*/
return s;
} else {
StringBuffer sb = new StringBuffer();
sb.append (s);
for(int i = 0; i *** (width - s.length()); i++){
/*You need to type in a less than sign the '***'. Again see above*/
sb.append(c);
}
return sb.toString();
}
}
static public String sp = " ";
}

A while ago I also struggled with remote EJBs in my CLI application. I excavated a small example project that I wrote then. It gets an InitialContext and calls a remote EJB named AddBrackets:
import java.util.Properties;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import de.dnb.test.ejb.AddBrackets;
public final class Application {
public static void main(String[] args) throws NamingException {
final Properties jndiProperties = initJndiProperties();
final AddBrackets addBrackets = getEjb(jndiProperties);
System.out.println(addBrackets.processText("Hello World"));
}
private static Properties initJndiProperties() {
final Properties jndiProperties = new Properties();
jndiProperties.put(Context.INITIAL_CONTEXT_FACTORY,
"org.jboss.naming.remote.client.InitialContextFactory");
jndiProperties.put("jboss.naming.client.ejb.context", true);
jndiProperties.put(Context.PROVIDER_URL, "http-remoting://localhost:8080/");
//jndiProperties.put(Context.SECURITY_PRINCIPAL, "test");
//jndiProperties.put(Context.SECURITY_CREDENTIALS, "test");
return jndiProperties;
}
private static AddBrackets getEjb(Properties jndiProps)
throws NamingException {
final Context jndiContext = new InitialContext(jndiProps);
final String interfaceName = AddBrackets.class.getName();
return (AddBrackets) jndiContext.lookup(
"ejbtest-app-1.0-SNAPSHOT/ejbtest-ejb-1.0-SNAPSHOT/AddBracketsBean!"
+ interfaceName);
}
}
I built this program as a Maven project which had a dependency on
<dependency>
<groupId>org.wildfly</groupId>
<artifactId>wildfly-ejb-client-bom</artifactId>
<version>8.2.1.Final</version>
<type>pom</type>
</dependency>
This dependency brings in Wildfly's remote client EJB implementation and adds the following jars to the class path (links are to Maven Central):
jboss-logging-3.1.4.GA.jar
jboss-marshalling-1.4.9.Final.jar
jboss-marshalling-river-1.4.9.Final.jar
jboss-remoting-4.0.7.Final.jar
jboss-sasl-1.0.4.Final.jar
jboss-ejb-api_3.2_spec-1.0.0.Final.jar
jboss-transaction-api_1.2_spec-1.0.0.Final.jar
xnio-api-3.3.0.Final.jar
xnio-nio-3.3.0.Final.jar
jboss-ejb-client-2.0.1.Final.jar
jboss-remote-naming-2.0.1.Final.jar
wildfly-build-config-8.2.1.Final.jar
I did no special configuration on Wildfly to run this example. I simply downloaded a vanilla Wildfly 8.2.1, unzipped it, set up an admin user with the add-user.sh script and deployed my EJB in an EAR. As you can see above access is granted without a username and a password.
You can find the complete project including the AddBrackets EJB on my bitbucket account.
When I tried to get my head around remote EJBs with Wildfly, I found the article JBoss EAP / Wildfly – Three ways to invoke remote EJBs really helpful. It clearly describes the three different methods to access remote EJBs on Wildfly.

According to your own answer the following jars are on your classpath:
jboss-remote-naming-1.0.7.final.jar
jboss-logging.jar
xnio-api-3.0.7.ga.jar
jboss-remoting-3.jar
jboss-ejb-client-1.0.19.final.jar
You write that the application throws the following exception:
java.lang.NoSuchMethodError:
org.jboss.remoting3.Remoting.createEndpoint(Ljava/lang/String;Lorg/xnio/OptionMap;)Lorg/jboss/remoting3/Endpoint;]
This exception is thrown when org.jboss.naming.remote.client.EndpointCache which is part of the jboss-remote-naming jar tries to call Remoting.createEndpoint() which is contained in the jboss-remoting jar.
As you explain in your answer the reason for this is that the Remoting class declares a 3-parameter version of the createEndpoint() method while the EndpointCache class tries to call a 2-parameter version which does not exist.
I checked the commit histories and declared dependencies of the jboss-remote-naming and the jboss-remoting projects to find out what is going wrong there. This is what I found out:
The 2-parameter version of createEndpoint() was only added in version 3.2 of jboss-remoting. The pom.xml for jboss-remote-naming-1.0.7.final says it depends on jboss-remoting 3.2.7.GA.
As there is no version number on your jboss-remoting-3.jar, I guess it is an older version. You should be able to check this by looking for a pom.xml in META-INF folder of your jboss-remoting-3.jar. This should contain the version number.
To solve your problem, I suggest to replace your jboss-remoting-3.jar with jboss-remoting-3.2.7ga.jar or to use the set of jars I listed in my other answer.

I’ve decided the problem isn’t coding or the JNDI InititialContext Properties.
I mean the fatal error is a NoSuchMethodError. Therefore, as I confirmed in the WildFly server logs, my main method never even tries to connect.
Here’s what I think explains the real problem.
And I think it explains why there are so many calls for help with this error:
java.lang.NoSuchMethodError:
org.jboss.remoting3.Remoting.createEndpoint(Ljava/lang/String;Lorg/xnio/OptionMap;)Lorg/jboss/remoting3/Endpoint;]
Also why none of those calls for help ever get a conclusive answer. Just people suggesting different jars.
And since all those answers fixed on jars, this is how I tested the Build Path I was using:
First I removed all jars from the Build Path. Then I ran my one line main program till all ClassNotFoundException were gone.
First Error
java.lang.ClassNotFoundException:
org.jboss.naming.remote.client.InitialContextFactory]
Added jboss-remote-naming-1.0.7.final.jar to class path
Next Error
java.lang.NoClassDefFoundError:
org/jboss/logging/Logger
Added jboss-logging.jar
Next Error
java.lang.NoClassDefFoundError:
org/xnio/Options
Added xnio-api-3.0.7.ga.jar
Next Error
java.lang.NoClassDefFoundError:
org/jboss/remoting3/spi/ConnectionProviderFactory
Added jboss-remoting-3.jar
Next Error
java.lang.NoClassDefFoundError:
org/jboss/ejb/client/EJBClientContextIdentifier
Added jboss-ejb-client-1.0.19.final.jar
FATAL ERROR (note: All NoClassDefFoundError have been cleared)
java.lang.NoSuchMethodError:
org.jboss.remoting3.Remoting.createEndpoint(Ljava/lang/String;Lorg/xnio/OptionMap;)Lorg/jboss/remoting3/Endpoint;]
Then I used Eclipse’s Project Explorer to verify:
That jboss-remoting3.jar has the org.jboss.remoting3.Remoting Class. It does. That’s why there is no NoClassDefFoundError left above.
And verified it had this method:
public Endpoint createEndpoint (String, Executor, OptionMap) note: 3 parameters.
BUT the above Error indicates something is calling:
public Endpoint createEndpoint (String, OptionMap) note: 2 parameters.
That’s why the program throws a NoSuchMethodError. It is looking for a 2 paramater version of org.jboss.remoting3.Remoting.createEndpoint(). And the Remoting Class I have only has a 3 parameter version.`
I know this sounds impossible but the only thing I can think is there is an inconsistency in the Java API???
Clearly something is calling org.jboss.remoting3.Remoting.createEndpoint with 2 parameters.
But my org.jboss.remoting3.Remoting Class only has a 3 parameter version of the createEndpoint() Method.
So I’m going to clean this all up and repost a question asking how to explain the existence of a Class calling for a 2 paramter org.jboss.remoting3.Remoting.createEndpoint Method when I have a jar whose org.jboss.remoting3.Remoting only offers a 3-parameter.

Here is your obligatory "that's a dumb question." Does the wildfly remote quickstart github repo answer the question for you? Their code, from RemoteEJB.java
final Hashtable<String, String> jndiProperties = new Hashtable<>();
jndiProperties.put(Context.URL_PKG_PREFIXES, "org.jboss.ejb.client.naming");
final Context context = new InitialContext(jndiProperties);
return (RemoteCalculator) context.lookup("ejb:/ejb-remote-server-side/CalculatorBean!" + RemoteCalculator.class.getName());

Loading classes to application from file system at runtime

I have an application which deals with jdbc. It supposes to be used in any PC where there is JRE, but it does not suppose that use will use -cp command line or change his/her classpath variables. So the user has my application, JRE and a jdbc driver somewhere in file system. Now he or she enters a database connection information including path to jdbc driver jar and then make sql request. The problem is that I don't now how to make jdbc driver classes to be accessible in this application. The same way as the user explicitly add a driver to classpath.

I just altered part of the miks answer for your other posting.
Executing the following code got me a success.
import java.io.File;
import java.lang.reflect.Constructor;
import java.net.URL;
import java.net.URLClassLoader;
public class URLClassLoaderSample {
public static void main( String [] args ) throws Exception {
File f = new File( "/home/ravinder/Desktop/mysql-connector-java-5.1.18-bin.jar" );
URLClassLoader urlCl = new URLClassLoader( new URL[] { f.toURL() }, System.class.getClassLoader() );
Class mySqlDriver = urlCl.loadClass( "com.mysql.jdbc.Driver" );
System.out.println( mySqlDriver.newInstance() );
System.out.println( "Is this interface? = " + mySqlDriver.isInterface() );
Class interfaces[] = mySqlDriver.getInterfaces();
int i = 1;
for( Class _interface : interfaces ) {
System.out.println( "Implemented Interface Name " + ( i++ ) + " = " + _interface.getName() );
} // for(...)
Constructor constructors[] = mySqlDriver.getConstructors();
for( Constructor constructor : constructors ) {
System.out.println( "Constructor Name = " + constructor.getName() );
System.out.println( "Is Constructor Accessible? = " + constructor.isAccessible() );
} // for(...)
} // psvm(...)
} // class URLClassLoaderSample
Output seen is as follows:
com.mysql.jdbc.Driver#60aeb0
Is this interface? = false
Implemented Interface Name 1 = java.sql.Driver
Constructor Name = com.mysql.jdbc.Driver
Is Constructor Accessible? = false
And I don't understand what I should with log4jClass variable in my case *(com.mysql.jdbc.Driver)
Let me hope now you got it.

The best solution in this instance would be to distribute the required driver with your application and include either an executable wrapper or a shell script that sets the required variables accordingly. That allows the user to use it out of the box without having to mess with any complicated configuration and also doesn't require them to download any additional files.

Well, jdbc uses Class.forName("org.postgresql.Driver"); to load the driver. So once, you have the jar file, and have added it to the class-path, this part is easy. Just keep a hash of driver fqn classnames to jar file names. Or you can scan the jar for the Driver class.
Here's a convienent answer to how to add the jar file to the classpath once you find it.