javap helper to quickly extract list of methods called from method

JavapHelper.java

package ....appsec.utils;

import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class JavapHelper {

    public Class target;

    public JavapHelper(Class clazz)
    {
        target = clazz;
    }
    public String pathToClass()
    {
        return this.target.getResource("/" + this.target.getName().replace(".","/") + ".class").toString();
    }

    /**
     * returns the result of javap with option -v on the provided class
     */
    public  String decompileClass() {
        String path                 = this.pathToClass();               // full path to class to map
        String[] args               = new String[] {"-v", path};        // trigger javap -v option
        StringWriter stringWriter   = new StringWriter();               // create StringWritter
        PrintWriter printWriter     = new PrintWriter(stringWriter);    // for PrintWriter

        com.sun.tools.javap.Main.run(args, printWriter);                // that is used by the javap main.run method

        printWriter.close();
        return stringWriter.toString();                                 // get result as string
    }

    /**
     * returns class contant pool values as hashmap
     */
    public HashMap<String,List<String>> constantPool()
    {
        String rawData  = this.decompileClass();
        String[] lines = rawData.split("\n");

        HashMap<String,List<String>> results = new HashMap<String,List<String>>();

        boolean insideConstantPool = false;
        for (String line :lines) {
            if(line.equals("Constant pool:"))                           // start of Constant pool data
            {
                System.out.println(line);
                insideConstantPool = true;
                continue;
            }
            if(insideConstantPool)
            {
                if (line.equals("{"))
                    break;

                String[] data = line.split("=",2)                       // extract the data to the right of the first =
                                    [1].trim()                          // [0] is the id [1] is the rest of the line
                                    .split(" ", 2);                     // split the constant pool name and its value
                if (data.length == 2) {
                    String key = data[0];                               // constant pool name
                    String value = data[1];                             // constant pool value
                    if (!results.containsKey(key))                      // if it is the first time we see this key
                        results.put(key, new ArrayList<>());
                    results.get(key).add(value.trim());                 // add key's value to key's list<String>
                }

            }
        }
        return results;
    }
    
    /**
     * returns list of methodsRef found in constant pool (these are the methods called by class' methods
     */
    public List<String> methodRefs()
    {
        ArrayList<String>            methodRefs   = new ArrayList<>();
        HashMap<String,List<String>> constantPool = this.constantPool();
        for(String entry : constantPool.get("Methodref"))                   // for each methodRef
        {
            String[] items = entry.split("//", 2);                          // split by comment
            methodRefs.add(items[1].trim());                                // use the right-hand side
        }
        return methodRefs;
    }
}

JavapHelperTest.java

package ....appsec.utils;


import org.junit.Before;
import org.junit.Test;

import java.util.HashMap;
import java.util.List;

import static org.hamcrest.CoreMatchers.*;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.greaterThan;


public class JavapHelperTest {

    JavapHelper javapHelper = null;
    Class       target      = null;

    @Before
    public void beforeClass()
    {
        target      = JavapHelper.class;
        javapHelper = new JavapHelper(target);
    }
    @Test
    public void pathToClass()
    {
        String result = javapHelper.pathToClass();
        assertThat(result, containsString(".../appsec/utils/JavapHelper.class"));
    }

    @Test
    public void decompileTest() {
        String result = javapHelper.decompileClass();
        assertThat(result, containsString("public java.lang.String decompileClass();"));
        assertThat(result, containsString("13: invokevirtual #6                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;"));
    }
    @Test
    public void constantPool() throws Exception {
        HashMap<String,List<String>> result = javapHelper.constantPool();
        assertThat(result.keySet().toArray(), is(new String[] { "Methodref", "Fieldref", "Utf8", "NameAndType", "Class", "String", "InterfaceMethodref"}));
    }
    @Test
    public void methodsRefs() throws Exception {
        List<String> result = javapHelper.methodRefs();

        assertThat(result.size(), greaterThan(10));
        assertThat(result, hasItem("java/lang/Object.\"<init>\":()V"));
        assertThat(result, hasItem("java/lang/StringBuilder.\"<init>\":()V"));
        assertThat(result, hasItem("java/lang/Class.getResource:(Ljava/lang/String;)Ljava/net/URL;"));
    }


}