How to Execute a JAR File with Additional Dependencies: -jar vs. -cp?

Call "java -jar MyFile.jar" with Additional Classpath Option

In Java, there are two ways to execute a JAR file: using the -jar option or specifying the classpath with -cp. However, attempting to combine both options leads to an error.

When using -jar, the Java Virtual Machine (JVM) assumes that the JAR file contains all necessary dependencies. Therefore, specifying an additional classpath with -cp is not recommended.

Instead, there are two alternative approaches:

Approach 1: Add JARs to the Main Manifest

1. Copy the required JAR files to a subfolder, such as "libs".
2. Use the task in Ant before building the JAR:

<code class="xml"><manifestclasspath property="myprogram.manifest.classpath" jarfile="MyProgram.jar">
  <classpath>
    <fileset dir="libs" includes="*.jar" />
  </classpath>
</manifestclasspath></code>

3. Create the JAR with the updated manifest:

<code class="xml"><jar destfile="MyProgram.jar" basedir="classes">
  <manifest>
    <attribute name="Main-Class" value="main.Main" />
    <attribute name="Class-Path" value="${myprogram.manifest.classpath}" />
  </manifest>
</jar></code>

By specifying the classpath in the manifest, java -jar MyProgram.jar will include all the dependencies.

Approach 2: Specify Classpath with -cp

1. Include all required JAR files in the classpath:

java -cp 'MyProgram.jar:libs/*' main.Main

Using the * syntax expands to include all JAR files in the "libs" directory.

Remember, it is crucial to choose either the -jar or -cp approach. Combining both can lead to classpath conflicts and errors.

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