Java – ant, jar files, and Class-Path oh the

antjarjava

I am trying to rearchitect my build technique for creating Java jar files which depend on common 3rd party jar files. (GlazedLists, Apache Commons, etc.)

I had been chucking them all into {Java JRE dir}/lib/ext so they would automatically be seen by the JRE, but that led to problems like not remembering that I need to distribute certain jar files, so I'd like to learn to be more explicit.

So I moved them all into c:\appl\java\common\, added them to the Eclipse build path, aand defined this in my ant file:

<path id="javac_classpath">
    <fileset dir="${libDir}">
        <include name="*.jar"/>
    </fileset>
    <fileset dir="c:/appl/java/common">
        <include name="*.jar"/>
    </fileset>
</path>

I have my Class-Path manifest header set to "." in my jar task but that doesn't seem to work even if I put the relevant jar files into the same directory as my application jar file. I can add them all manually one-by-one to the Class-Path header, but I'm wondering, is there an easier way to get the Class-Path header setup properly?

Best Answer

This is all you need:

<path id="build-classpath">
    <fileset dir="${dist}/lib">
        <include name="*.jar"/>
    </fileset>
</path>
<manifestclasspath property="lib.list" jarfile="${dist}/lib/myprog.jar">
    <classpath refid="build-classpath"/>
</manifestclasspath>
<jar jarfile="${dist}/lib/myprog.jar"
     basedir="${build}"
     includes="com/my/prog/**" >
    <manifest>
        <attribute name="Main-Class" value="com.my.prog.MyProg"/>
        <attribute name="Class-Path" value="${lib.list}"/>
    </manifest>
</jar>

As you can probably see, it assumes you've compiled your Java classes and output them to ${build}. It also assumes you've copied your jarfiles to ${dist}/lib.

That said, it would be worth looking into other build systems which have built-in support for dependencies, such as Maven and Gradle. These other build systems have already thought through many common project structures and build operations, so you don't have to script everything down to the last detail.

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Java – How to test a class that has private methods, fields or inner classes

Update:

Some 10 years later perhaps the best way to test a private method, or any inaccessible member, is via @Jailbreak from the Manifold framework.
@Jailbreak Foo foo = new Foo();
// Direct, *type-safe* access to *all* foo's members
foo.privateMethod(x, y, z);
foo.privateField = value;
This way your code remains type-safe and readable. No design compromises, no overexposing methods and fields for the sake of tests.

If you have somewhat of a legacy Java application, and you're not allowed to change the visibility of your methods, the best way to test private methods is to use reflection.

Internally we're using helpers to get/set private and private static variables as well as invoke private and private static methods. The following patterns will let you do pretty much anything related to the private methods and fields. Of course, you can't change private static final variables through reflection.

Method method = TargetClass.getDeclaredMethod(methodName, argClasses);
method.setAccessible(true);
return method.invoke(targetObject, argObjects);

And for fields:

Field field = TargetClass.getDeclaredField(fieldName);
field.setAccessible(true);
field.set(object, value);

Notes:
1. TargetClass.getDeclaredMethod(methodName, argClasses) lets you look into private methods. The same thing applies for getDeclaredField.
2. The setAccessible(true) is required to play around with privates.

Java – What are the differences between a HashMap and a Hashtable in Java

There are several differences between HashMap and Hashtable in Java:

Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn't be as easy if you were using Hashtable.

Since synchronization is not an issue for you, I'd recommend HashMap. If synchronization becomes an issue, you may also look at ConcurrentHashMap.

Best Answer

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