Question

I am making software that will need to dynamically create java bytecode, and possibly even make it a runnable jar.

My current idea is to create a new .java file and compile it at runtime. I can create the file, but I’m not sure how to compile it at runtime, and make it a runnable jar. Any help would be greatly appreciated.

public static String generate(String filePath) {
    try {
        File file = new File("Test.java");
        if(!file.exists())file.createNewFile();
        FileWriter write = new FileWriter(filePath+".java");
        BufferedWriter out = new BufferedWriter(write);
        out.write(
                "public class Test {\n\t" +
                    "public static void main(String[] args){\n\t\t"+
                        "System.out.println(\"Working\");\n\t"+
                    "}\n" +
                "}"

                );
        out.close();

    } catch (Exception e) {// Catch exception if any
        return "Error: " + e.getMessage();
    }
    return "Test.java created!";
}

Answer 1

To compile Java code, you can use the Java Compiler API.

To generate byte code directly, you can use tools like ASM.

To generate an executable JAR, create a JarOutputStream with a manifest that declares the main class.