Re: Using sun javac to parse java source

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <>
Wed, 24 Aug 2011 19:19:44 -0400
On 8/24/2011 4:51 AM, Sebastian wrote:

Am 24.08.2011 01:00, schrieb Arne Vajh?j:

On 8/23/2011 4:24 PM, Alex J wrote:

I'm curious whether it is possible to use JavacParser -
- built-in to OpenJDK to parse standalone java files (though claimed
to be "internal use only API"). I googled but I've found no answers.

Java 1.6 and newer contains a supported callable Java compiler.

Use that.

If you only want to syntax check you will need to discard the
generated byte code in case of success, but that is easy.

The API is a bit complex many would say over engineered, but
it works fine.

You might find a detailed example useful. There is an article
about "Dynamic Code Generation with Java Compiler API in Java 6"
by Swaminathan Bhaskar at

The article shows how to compile source from strings to byte arrays.

I have a slightly differentexample - see below.



package test;

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;


public class JC {
     public static void dynamicCall(String clznam, String src, String
cp, String metnam) throws Exception {
         SpecialClassLoader xcl = new SpecialClassLoader();
         compileMemoryMemory(src, cp, clznam, xcl, System.err);
         Class<?> c = Class.forName(clznam, true, xcl);
         Object o = c.newInstance();
         c.getMethod(metnam, new Class[] { }).invoke(o, new Object[] { });
     public static void compileMemoryMemory(String src, String cp,
String name, SpecialClassLoader xcl, PrintStream err) {
         JavaCompiler javac = ToolProvider.getSystemJavaCompiler();
         DiagnosticCollector<JavaFileObject> diacol = new
         StandardJavaFileManager sjfm =
javac.getStandardFileManager(diacol, null, null);
         SpecialJavaFileManager xfm = new SpecialJavaFileManager(sjfm, xcl);
         CompilationTask compile = javac.getTask(null, xfm, diacol,
Arrays.asList(new String[] { "-classpath", cp }), null,
JavaFileObject[] { new MemorySource(name, src) }));
         boolean status =;
         if(err != null) {
             err.println("Compile status: " + status);
             for(Diagnostic<? extends JavaFileObject> dia :
diacol.getDiagnostics()) {

class MemorySource extends SimpleJavaFileObject {
     private String src;
     public MemorySource(String name, String src) {
         super(URI.create("string:///" + name.replace(".", "/") +
".java"), Kind.SOURCE);
         this.src = src;
     public CharSequence getCharContent(boolean ignoreEncodingErrors) {
         return src;
     public OutputStream openOutputStream() {
         throw new IllegalStateException();
     public InputStream openInputStream() {
         return new ByteArrayInputStream(src.getBytes());

class MemoryByteCode extends SimpleJavaFileObject {
     private ByteArrayOutputStream baos;
     public MemoryByteCode(String name) {
         super(URI.create("byte:///" + name.replace(".", "/") +
".class"), Kind.CLASS);
     public CharSequence getCharContent(boolean ignoreEncodingErrors) {
         throw new IllegalStateException();
     public OutputStream openOutputStream() {
         baos = new ByteArrayOutputStream();
         return baos;
     public InputStream openInputStream() {
         throw new IllegalStateException();
     public byte[] getBytes() {
         return baos.toByteArray();

class SpecialJavaFileManager extends
ForwardingJavaFileManager<StandardJavaFileManager> {
     private SpecialClassLoader xcl;
     public SpecialJavaFileManager(StandardJavaFileManager sjfm,
SpecialClassLoader xcl) {
         this.xcl = xcl;
     public JavaFileObject getJavaFileForOutput(Location location,
String name, JavaFileObject.Kind kind, FileObject sibling) throws
IOException {
         name = sibling.getName().substring(1,
sibling.getName().length() - 5).replace("/", ".");
         MemoryByteCode mbc = new MemoryByteCode(name);
         xcl.addClass(name, mbc);
         return mbc;

class SpecialClassLoader extends ClassLoader {
     private Map<String,MemoryByteCode> m;
     public SpecialClassLoader() {
         m = new HashMap<String, MemoryByteCode>();
     protected Class<?> findClass(String name) throws
ClassNotFoundException {
         MemoryByteCode mbc = m.get(name);
         if(mbc != null) {
             return defineClass(name, mbc.getBytes(), 0,
         } else {
             throw new ClassNotFoundException(name);
     public void addClass(String name, MemoryByteCode mbc) {
         m.put(name, mbc);

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