How to create and use library JAR files with command-line tools?

Question

Development Tools -> General Questions:
I am trying to figure out how to put utility classes into JAR files and then compile and run applications against those JAR files using the command-line javac, jar, and java tools. I am using jdk1.7.0_17 on Debian GNU/Linux 6.0.7.
I have posted a simple example with one utility class, one console application class, and a Makefile:
http://holgerdanske.com/users/dpchrist/java/examples/jar-20130520-2134.tar.gz
Here is a console session:
2013-05-20 21:39:01 dpchrist@desktop ~/sandbox/java/jar
$ cat src/com/example/util/Hello.java
package com.example.util;
public class Hello {
    public static void hello(String arg) {
     System.out.println("hello, " + arg);
2013-05-20 21:39:12 dpchrist@desktop ~/sandbox/java/jar
$ cat src/com/example/hello/HelloConsole.java
package com.example.hello;
import static com.example.util.Hello.hello;
public class HelloConsole {
    public static void main(String [] args) {
     hello("world!");
2013-05-20 21:39:21 dpchrist@desktop ~/sandbox/java/jar
$ make
rm -f hello
find . -name '*.class' -delete
javac src/com/example/util/Hello.java
javac -cp src src/com/example/hello/HelloConsole.java
echo "java -cp src com.example.hello.HelloConsole" > hello
chmod +x hello
2013-05-20 21:39:28 dpchrist@desktop ~/sandbox/java/jar
$ ./hello
hello, world!I believe I am looking for:
1. Command-line invocation of "jar" to put the utility class bytecode file (Hello.class) into a JAR?
2. Command-line invocation of "javac" to compile the application (HelloConsole.java) against the JAR file?
3. Command-line invocation of "java" to run the application (HelloConsole.class) against the JAR file?
I already know how t compile the utility class file.
Any suggestions?
TIA,
David

Answer 1

I finally figured it out:
1. All name spaces must match -- identifiers, packages, file system, JAR contents, etc..
2. Tools must be invoked from specific working directories with specific option arguments, all according to the project name space.
My key discovery was that if the code says
import com.example.util.Hello;then the JAR must contain
com/example/util/Hello.classand I must invoke the compiler and interpreter with an -classpath argument that is the full path to the JAR file
-classpath ext/com/example/util.jarThe code is here:
http://holgerdanske.com/users/dpchrist/java/examples/jar-20130525-1301.tar.gz
Here is a console session that demonstrates building and running the code two ways:
1. Compiling the utility class into bytecode, compiling the application class against the utility bytecode, and running the application bytecode against the utility bytecode.
2. Putting the (previously compiled) utility bytecode into a JAR and running the application bytecode against the JAR. (Note that recompiling the application against the JAR was unnecessary.)
(If you don't know Make, understand that the working directory is reset to the initial working directory prior to each and every command issued by Make):
2013-05-25 14:02:47 dpchrist@desktop ~/sandbox/java/jar
$ cat apps/com/example/hello/Console.java
package com.example.hello;
import com.example.util.Hello;
public class Console {
    public static void main(String [] args) {
     Hello.hello("world!");
2013-05-25 14:02:55 dpchrist@desktop ~/sandbox/java/jar
$ cat libs/com/example/util/Hello.java
package com.example.util;
public class Hello {
    public static void hello(String arg) {
     System.out.println("hello, " + arg);
2013-05-25 14:03:03 dpchrist@desktop ~/sandbox/java/jar
$ make
rm -rf bin ext obj
mkdir obj
cd libs; javac -d ../obj com/example/util/Hello.java
mkdir bin
cd apps; javac -d ../bin -cp ../obj com/example/hello/Console.java
cd bin; java -cp .:../obj com.example.hello.Console
hello, world!
mkdir -p ext/com/example
cd obj; jar cvf ../ext/com/example/util.jar com/example/util/Hello.class
added manifest
adding: com/example/util/Hello.class(in = 566) (out= 357)(deflated 36%)
cd bin; java -cp .:../ext/com/example/util.jar com.example.hello.Console
hello, world!
2013-05-25 14:03:11 dpchrist@desktop ~/sandbox/java/jar
$ tree -I CVS .
|-- Makefile
|-- apps
|   `-- com
|       `-- example
|           `-- hello
|               `-- Console.java
|-- bin
|   `-- com
|       `-- example
|           `-- hello
|               `-- Console.class
|-- ext
|   `-- com
|       `-- example
|           `-- util.jar
|-- libs
|   `-- com
|       `-- example
|           `-- util
|               `-- Hello.java
`-- obj
    `-- com
        `-- example
            `-- util
                `-- Hello.class
19 directories, 6 filesHTH,
David