StringFinder.java

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.tree.AbstractInsnNode;
import org.objectweb.asm.tree.ClassNode;
import org.objectweb.asm.tree.LdcInsnNode;
import org.objectweb.asm.tree.MethodNode;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.util.AbstractMap.SimpleEntry;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

public class StringFinder {

    public static void main(String[] args) throws IOException {
        List<Map.Entry<String, String>> results = new ArrayList<>();

        try (JarFile in = new JarFile(new File("input.jar"))) {
            for (Enumeration<JarEntry> entries = in.entries(); entries.hasMoreElements(); ) {
                JarEntry entry = entries.nextElement();

                if (entry.isDirectory() || !entry.getName().endsWith(".class")) {
                    continue;
                }

                try (InputStream entryIn = in.getInputStream(entry)) {
                    ClassReader cr = new ClassReader(entryIn);

                    ClassNode classNode = new ClassNode();
                    cr.accept(classNode, 0);

                    for (MethodNode methodNode : classNode.methods) {
                        Iterator<AbstractInsnNode> insnIterator = methodNode.instructions.iterator();
                        while (insnIterator.hasNext()) {
                            AbstractInsnNode insnNode = insnIterator.next();
                            if (insnNode.getType() != AbstractInsnNode.LDC_INSN) {
                                continue;
                            }

                            Object constant = ((LdcInsnNode) insnNode).cst;
                            if (constant instanceof String) {
                                String str = ((String) constant);
                                results.add(new SimpleEntry<>(classNode.name + "." + methodNode.name, str));
                            }
                        }
                    }
                }
            }
        }

        System.out.println("Found " + results.size() + " results");
        for (Map.Entry<String, String> entry : results) {
            System.out.println(entry.getKey() + ":  '" + entry.getValue() + "'");
        }
    }

}