Develop Reference

Java Ant Job how to ship Log4j jar with my jar

Just trying to upgrade some old stuff and part of that I need to bundle my custom jar which uses Log4j. I did add the following for my <javac> task which compiles successfully.
<path id="my.classpath">
<fileset dir="${mainpath}">
<include name="**/*log4j*.jar"/>
</fileset>
</path>
<javac srcdir="src/java" destdir="build/filez/java" debug="on" deprecation="no"
includes="my/instruments/**/*, org/apache/log4j/**/*">
<classpath refid="my.classpath"/>
</javac>
However, In my <jar> job I cannot see any log4j dependency packed with my custom jar. This might be a silly question, but how do ensure that my custom-jar does not fail when called from another application since the dependency isn't packed? Will it be okay as long as log4j has been loaded by classloader in the target application?
Additionally, do I need to add something in my Manifest for this?
I cannot use Maven (yes I know) for a little while, so cannot solve this problem with maven

You can use One-JAR to package your code along with it's dependencies into one big executable JAR.
It can be used either as a standalone tool from the command line or as a task defined in build.xml.
<!-- Construct the One-JAR file -->
<one-jar destfile="hello.jar" manifest="hello.mf">
<main>
<!-- Construct main.jar from classes and source code -->
<fileset dir="${classes.dir}/src"/>
</main>
<lib>
<fileset file="${build.dir}/lib.jar" />
</lib>
</one-jar>

Javac inexplicably failing on Hudson

Our application is built my Hudson from Ant scripts. In my latest work I've recently included Maven. Now Hudson's build process fails when it reaches the compilation task without any explanation.
Hudson build:
[echo] Using Maven Repo at ../.maven/repo/
[javac] Compiling 134 source files to C:\Users\administrator1\.hudson\jobs\SAP_RC\workspace\current\classes
BUILD FAILED
C:\Users\administrator1\.hudson\jobs\SAP_RC\workspace\current\build.xml:68: Error running C:\Program Files (x86)\Java\jdk1.8.0_66\bin\javac.exe compiler
Ant script:
<javac classpathref="lib" destdir="${classesDir}" debug="true" debuglevel="lines,vars,source" verbose="true" fork="true" nowarn="true" memoryMaximumSize="320m" srcdir="${srcDir}" includeantruntime="false" />
I specifically included the Maven repo into the classpath, and that's when it fails inexplicably. When I remove the Maven repo the build throws a compilation error complaining that it can't find Maven dependencies. This makes me suspect that I'm hitting some classpath length limit.
I did it this way because I'm not sure what is the correct way to include Maven dependencies into the classpath. If there is a better way please tell me and I'll open a new question specifically for that.

It seems as though my wildcard in my fileset was the culprit.
<path id="lib">
<fileset dir="${env.maven_repo}">
<include name="*/**"/>
</fileset>
</path>
I changed the ** to *.jar and the build process is no longer (inexplicably) failing.
<path id="lib">
<fileset dir="${env.maven_repo}">
<include name="*/*.jar"/>
</fileset>
</path>

Why combine all jars together?

I have create RESTful web service based on the JAX-RS and used Jersey embedded web server. My ant script compiles code successfully while it gives me error ClassNotFoundException when I run my main class. So after doing research I came up with solution & here it goes java build ant file with external jar files . What I did was created a bundled jar file try to execute that & it works perfectly fine. I want to know the reason behind :
why this solution works ?
Why I should combine all jar file ?
Is it similar to war file which we create following J2EE architecture otherwise war will not be extracted by server ( say TOMCAT ) & in my case jar file for Jersey embedded HTTP server?
EDIT:
Here is my ant build.xml file
<property name="lib.dir" value="${user.dir}/lib"/>
<property name="build.dir" value="${user.dir}/build"/>
<property name="build.lib.dir" value="${build.dir}/lib"/>
<property name="build.classes.dir" value="${build.dir}/classes"/>
<property name="src.dir" value="${user.dir}/src/main/java"/>
<property name="main.class" value="com.assignment.ConsoleServer"/>
<path id="classpath">
<fileset dir="${lib.dir}" includes="**/*.jar"/>
</path>
<target name="clean">
<delete dir="${build.dir}"/>
</target>
<target name="init" depends="clean">
<!-- Create the build directory structure used by compile -->
<mkdir dir="${build.dir}"/>
<mkdir dir="${build.classes.dir}"/>
</target>
<target name="copy_jars" depends="init" >
<copy todir="${build.lib.dir}" >
<fileset dir="${lib.dir}">
<include name="**/*.jar" />
</fileset>
</copy>
</target>
<target name="compile" depends="copy_jars">
<javac srcdir="${src.dir}" destdir="${build.classes.dir}" classpathref="classpath" includeantruntime="false"/>
</target>
<target name="jar" depends="compile">
<jar destfile="${build.dir}/${ant.project.name}.jar" basedir="${build.classes.dir}">
<manifest>
<attribute name="Main-Class" value="${main.class}"/>
</manifest>
<zipgroupfileset dir="${lib.dir}" includes="*.jar"/>
</jar>
</target>
<target name="run" depends="jar">
<java fork="true" classname="${main.class}">
<classpath>
<path refid="classpath"/>
<path location="${build.dir}/${ant.project.name}.jar"/>
</classpath>
</java>
</target>
Here is my folder structure
P.S. I am not java expert so pardon me if this question is stupid.

Why this solution works?
In your particular case, you probably didn't include all of the necessary dependencies in your deployment in your previous. (It is not clear from your question how you were originally doing the deployment.)
Now you have put all of the application and dependent class files, etc into one JAR file, and presumably you are deploying / running that file. It works because now it has everything that it needs to run ... which it didn't before.
Why I should combine all jar file?
In your case I suspect that it was not strictly necessary. There was probably a way to "deploy" all of the dependencies without combining them into a single JAR file.
However, there is one case where a "uber-jar" has advantages. That is when the JAR is intended to be an "executable" JAR, and you want to be able to distribute / install it as a single file. (And executable JAR
file can refer to external JARs, etc, but the way that you have to do
it is "fragile".)
Is it similar to war file ... ?
Sort of, though a WAR file contains JAR files ... and typically other kinds of resources that the web-container understands.

The solution works because you packed all you service classes and depending libraries in one jar. That jar and everything inside will be in the class path and visible to your execution virtual machines class loader.
If you leave your depending libraries out your Jersey Web server needs to have them on it's class path, then you wouldn't get ClassNotFoundExcpetion
You shouldn't pack web application in single jar. You should crate war file where you dependencies will be placed inside WEB-INF/lib. You would easily then deploy that war on any application server. Switching to Maven instead of Ant can help a lot.
EDIT: After you added more details to description and ant
If you don't want to use fat-jar you can either
modify your antjava task to specify classpath that will reference
all external libraries (basically telling ant how to build
-classpath parameter for java -jar command
even better, modify your javac ant task by making complete Manifest file that specifies Class-Path correctly, take a better
look at the solution (at the bottom) of the answer you linked (java build ant file with external jar files)
For completness reference on Manifest here

Java - How to create JavaDocs in Apache Ivy

I know how to create javadocs for my source file in Apache Ant Build.
<target name="doc" description="generate documentation">
<delete dir="${doc.dir}"/>
<mkdir dir="${doc.dir}"/>
<javadoc sourcepath="${source.dir}" destdir="${doc.dir}"/>
</target>
But I don't know how to create them in Apache Ivy.
Could some one show me a sample example ?

Apache Ivy is a dependency management library for use with (not a replacement for) Apache Ant. Therefore, you will use the same <javadoc> task as always.

Apache Ivy is a dependency manager that works with Ant (a build manager). Apache Ivy is usually (or possible always?) used with Ant to handle builds. Since javadoc creation is a build task not a dependency task, it wouldn't make sense to generate javadocs using Ivy.

It looks like you're going around in a circle here. Ivy works with Ant. You still have a build.xml file that you use for your builds. The ivy.xml file simply contains a list of the third-party jars your project needs in order to build. Thus, the direct answer to your question would be:
Put the following in your build.xml:
<target name="doc" description="generate documentation">
<delete dir="${doc.dir}"/>
<mkdir dir="${doc.dir}"/>
<javadoc sourcepath="${source.dir}" destdir="${doc.dir}"/>
</target>
When you use Ivy, you still use Ant. And, you still have a build.xml file. And, you still write compose your build with various Ant tasks.
Download this project. It's a simple build that contains three class files and a build.xml file. You will notice there's a jar directory with the following two jars:
commons-logging-1.1.1.jar
spring.jar
If you look at lines 36 to 40 of the build.xml file, the project is creating a compile classpath like this:
<path id="java">
<fileset file="jar/spring.jar"/>
<fileset file="jar/commons-logging-1.1.1.jar"/>
</path>
So, when he compiles, he does this:
<javac destdir="bin">
<src path="${src}"/>
<classpath refid="java"/>
</javac>
Now, let's look at how this may change with Ivy. In Ivy, I create a ivy.xml file that contains a description of what jars I need. However, I only have to specify classes I use directly. In this case, I only need the spring.jar. Here's my ivy.xml:
<ivy-module version="1.0>
<info organisation="com.seantheflexguy"
name="ContextExample"
revision="1.0"/>
<configurations>
<conf="default" visibility="public"/>
<conf="compile" visibility="public"/>
</configurations>
<dependencies>
<dependency org="org.springframework" name="spring"
rev="2.0.4" conf="compile->default"/>
</dependencies>
</ivy-module>
Now, instead, of using the jars in the jar directory, I'll have Ivy construct the classpath:
<ivy:resolve/>
<ivy:cachepath pathid="java"/>
<javac destdir="bin">
<src path="${src}"/>
<classpath refid="java"/>
</javac>
Notice instead of using the <path> task to create a classpath, I use two Ant tasks that Ivy uses. The <ivy:resolve/> looks at my ivy.xml and resolves my dependencies on the jars I request. These jars will be downloaded into my $HOME/.ivy2/cache directory.
The <ivy:cachepath> task creates a classpath I'm calling the classpath java because that's what it was previously called.
With those two Ivy tasks, I've created a classpath that I can use with the <javac> task. In fact, I'm not even bothering to change the <javac> task.
So, in Ivy:
I still need my build.xml. It's how I define the various build tasks I need to do. In fact, Ivy defines even more Ant tasks I need in my build.xml file.
The ivy.xml file simply defines my jar dependencies. When I implement Ivy in this project, I can delete the jar directory.
Does this help you understand how Ivy works?

Log4j not being added to classpath in Ant

I'm attempting to add Log4j to my project's classpath in Ant which creates an executable JAR, but it appears that it's not being added properly.
Here is the path component of my Ant build script:
<path id="classpath.compile">
<fileset dir="${dir.myLibs}">
<include name="**/*.jar"/>
</fileset>
<pathelement location="${dir.webContent}/WEB-INF/lib/log4j.jar" />
</path>
The compile target looks like this:
<target name="-compile">
<javac destdir="${dir.binaries}" source="1.6" target="1.6" debug="true" includeantruntime="false">
<src path="${dir.source}"/>
<classpath refid="classpath.compile"/>
</javac>
</target>
Tthe target that creates the JAR:
<target name="-createJar" >
<jar jarfile="${path.jarFile}"
manifest="${dir.source}\META-INF\MANIFEST.MF">
<fileset dir="${dir.binaries}" casesensitive="yes">
<exclude name="**/*.java"/>
</fileset>
</jar>
</target>
Lastly, the MANIFEST.MF:
Manifest-Version: 1.0
Class-Path: ../../../WebContent/WEB-INF/lib/log4j.jar (what is this pathing relative to?)
Main-Class: foo.Bar
The JAR is created, but when I execute it, I get:
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/log4j/Logger...
Any thoughts as to what I'm doing wrong?

It looks from the classpath in your MANIFEST that you are trying to reference a jar inside your jar. The only two ways to make that work AFAIK are 1) a special classloader, like #infosec812 mentions, or 2) by exploding the jar dependencies directly into the root of your jar. Either is workable, but I don't see either of them happening in your ant script.
If you're trying to reference a jar outside of your jar, your relative classpath is relative to the location of the jar you are executing. Make sure the referenced jar exists in that location.

I'm guessing that you're running the Java program as follows
java -jar myapp.jar
In this case you'll need to specify the Class-Path attribute in the manifest. I suggest you also check out the manifestclasspath task

Creating the jar does not include the linked libraries in the jar. You would have to have the required jars in your execution classpath in order to run it that way. Or, you could use the solution I use, which is to create a one-jar archive. It adds a specialized class loader for your application into the resulting jar and also packages your required jars in to the final executable jar. It works really well for deploying neat, simple to use packages.