Compiling Lambda Expression from String in Janino

Question

I am trying to compile a class from a String using Janino. The class contains a lambda expression inside a function but it seems to not recognize the reference operator "->" and "::".

I am getting a CompileException The complete stake trace Exception in thread "main" org.codehaus.commons.compiler.CompileException: Line 1, Column 346: Unexpected token ">" in primary

Below is the code I am using,

public class LambdaFromJanino{

      public static void main(String[] args) throws Exception
        {
            String CLASS_NAME = "Foo";
            String codeStr = "import java.util.Arrays;" + 
                        "import java.util.List;"+
                        "import java.util.stream.Collectors;"+
                        "public class " + CLASS_NAME + " {" +
                        "public static void main(String[] args) {" +
                        "System.out.println(\"Hello \" + args[0]);" +
                        "List<String> result = lambdaOut(args);"+
                        //"result.forEach(System.out::println);"+
                        "System.out.println(\"this is result \"+result.get(0));"+
                        "}" +
                        "static List lambdaOut(String[] arr)  {  " +
                        "return  Arrays.stream(arr).map( x -> x.replaceAll(\"[a-zA-Z]\", \"\"))" +
                        ".collect(Collectors.toList()); }; " +
                        "}";
            SimpleCompiler compiler = new SimpleCompiler();
            compiler.cook( codeStr ); // compile the string
            // get the loaded class
            Class<?> cl = compiler.getClassLoader().loadClass(CLASS_NAME);
            // Invoke the "public static main(String[])" method
            Method mainMeth = cl.getMethod("main", new Class[] { String[].class });
            String[] methArgs = new String[] { args[0], args[1], args[2] }; // one input
            mainMeth.invoke(null, new Object[] { methArgs });
        } 
}

Yes, I am using Java 8 and this lambda expression works fine when called directly in main method. — Shafaq, Aug 20 '20 at 12:26
Issue is not with Lambda expression, it's with assignment of `List result`. — Sagar Gangwal, Aug 20 '20 at 12:28
Even if you try like this static it's not working `List result= new ArrayList();` — Sagar Gangwal, Aug 20 '20 at 12:29
@SagarGangwal List result= new ArrayList(); is working fine just need to add "import java.util.ArrayList;" in imports. So if I just return the list in the function lambdaOut without any lambda expression it works fine. — Shafaq, Aug 20 '20 at 12:49
What i understood from library it's not able to parse characters like `>` or `<`. — Sagar Gangwal, Aug 20 '20 at 12:52

score 0 · Answer 1 · answered Aug 20 '20 at 12:56

Try below code, it will help to resolve your problem.

As you are not collection result me lambda expression, here i had attached \"\")).collect(Collectors.toList())\n" to resolve it.

    public static void main(String[] args) throws Exception
                {
                    String CLASS_NAME = "Foo";
                    String codeStr = "import java.util.Arrays;" + 
                                "import java.util.List;"+
                                "import java.util.stream.Collectors;"+
                                "public class " + CLASS_NAME + " {" +
                                "public static void main(String[] args) {" +
                                "System.out.println(\"Hello \" + args[0]);" +
                                "List<String> result = lambdaOut(args);"+
                                //"result.forEach(System.out::println);"+
                                "System.out.println(\"this is result \"+result.get(0));"+
                                "}" +
                                "static List lambdaOut(String[] arr)  {  " +
"return  Arrays.stream(arr).map( x -> x.replaceAll(\"[a-zA-Z]\", \"\")).collect(Collectors.toList())\n" +
                    ".collect(Collectors.toList()); }; \n" +
                    "}";

Compiling Lambda Expression from String in Janino

1 Answers1