You can't execute an arbitrary method directly from a shell script, you'll need to have that method exposed externally in some way.

The simplest way of course is to write a main method that directly invokes the code you want to test.

Alternatively, you could make use of a Java application that takes parameters to act as a sort of launcher. In its crudest form you can imagine an app that takes a classname and method name as arguments, then instantiates the class and invokes the method via reflection. In a similar vein, but a bit more elegant, we use an app that invokes operations exposed via JMX in order to fire certain methods on a server when required.

Ultimately though, bash (or equivalent) doesn't understand JVM bytecode. You will need to launch a Java process to run the method, which will involve executing some main method that in turn invokes what you need.

You can use Apache Commons exec library also.

Example :

package testShellScript;

import java.io.IOException;
import org.apache.commons.exec.CommandLine;
import org.apache.commons.exec.DefaultExecutor;
import org.apache.commons.exec.ExecuteException;

public class TestScript {
    int iExitValue;
    String sCommandString;

    public void runScript(String command){
        sCommandString = command;
        CommandLine oCmdLine = CommandLine.parse(sCommandString);
        DefaultExecutor oDefaultExecutor = new DefaultExecutor();
        oDefaultExecutor.setExitValue(0);
        try {
            iExitValue = oDefaultExecutor.execute(oCmdLine);
        } catch (ExecuteException e) {
            System.err.println("Execution failed.");
            e.printStackTrace();
        } catch (IOException e) {
            System.err.println("permission denied.");
            e.printStackTrace();
        }
    }

    public static void main(String args[]){
        TestScript testScript = new TestScript();
        testScript.runScript("sh /root/Desktop/testScript.sh");
    }
}

For further reference, An example is given on Apache Doc also.

The problem is that the shell redirection (<) sends the file over the ssh tunnel. And the Java class is expecting not the file, but a string with the "filename" of a local file that will be read with a FileReader.

Instead of passing the filename to the FileReader, read from the standard input.

InputStreamReader isReader = new InputStreamReader(System.in);
BufferedReader iR  = new BufferedReader (isReader);

Used this as a reference: https://stackoverflow.com/questions/5724646/how-to-pipe-input-to-java-program-with-bash

Now your class will be:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.OutputStreamWriter;
import java.io.InputStreamReader;

public class ReadFirstLine 
{
    public static void main(String[] args) throws Exception 
    {
       String filename = args[0];
       System.out.println(filename);

       //BufferedReader iR  = new BufferedReader (new FileReader(filename));
       InputStreamReader isReader = new InputStreamReader(System.in);
       BufferedReader iR  = new BufferedReader (isReader);

       BufferedWriter oW = new BufferedWriter(new OutputStreamWriter(System.out));

       //outputWriter.write(iR.readLine());
       System.out.println(iR.readLine());

       iR.close();
       oW.close();
    }
}

But for this task I would definitely use instead:

head -1 filename.txt

:)

Adding & to the end will send Java to the background. That means that Java will run in the background and the shell script will continue running. But once the shell script reaches the end, it will wait for Java to finish before it exits. You have to disown the java program, and then the script will exit and java will continue to run. Just add the command "disown" directly below where you run the jar file.

you can create a shell with name say "run.sh" (note .sh extension which tell it is a shell script) and copy it in /usr/local/bin directory.

1.Script (run.sh)

#!/bin/sh

arg1=$1
arg2=$2

##directory where jar file is located    
dir=/directory-path/to/jar-file/

##jar file name
jar_name=json-simple-1.1.1.jar

## Permform some validation on input arguments, one example below
if [ -z "$1" ] || [ -z "$2" ]; then
        echo "Missing arguments, exiting.."
        echo "Usage : $0 arg1 arg2"
        exit 1
fi

java -jar $dir/$jar_name arg1 arg2

2. copy the script in /usr/local/bin

   cp run.sh /usr/local/bin

3. Give execute permission to the script

   chmod u+x /usr/local/bin/test.sh

4. now you can type just word run or run.sh on command line : shell will auto-complete the script name and also it can executed by pressing enter key.