Include an in-memory jar file for JSR-199 compilation

Question

I want to compile a source file in memory, which requires a jar file that is also represented in memory. I used the JavaSourceFromString class recommended in the documentation for the class JavaCompiler and in a demo I found online that shows how to compile sources represented as String in memory. To represent the jar file, I used a similar trick to JavaSourceFromString:
public class JarJavaFileObjectFromByteArray extends SimpleJavaFileObject {
   * The contents of this jar file.
  private final byte[] contents;
   * Constructs a new JarJavaFileObjectFromByteArray given the name and binary
   * contents of a jar file.
   * @param name the name of this jar file
   * @param contents the contents of this jar file
  public JarJavaFileObjectFromByteArray(String name, byte[] contents) {
    super(newURI(name), Kind.OTHER);
    this.contents = contents;
  ... // code not shown ensures that the URI returned from newURI is of the form,
      // for instance, bytes:///MathConstants.jar, if the name of the jar file is MathConstants.jar
  @Override
  public InputStream openInputStream() throws IOException {
    return new ByteArrayInputStream(contents);
}However, I do not know how to alert the compiler that this jar file should be on the classpath. I tried this:
List<String> options = Arrays.asList(" -classpath bytes:///MathConstants.jar ");
CompilationTask task = compiler.getTask(null, fileManager, null, options, null, compilationUnits);but I get the following error when calling getTask:
java.lang.IllegalArgumentException: invalid flag: -classpath bytes:///MathConstants.jarI assume there is some way to tell the compiler, "look at the MathConstants.jar file that I am storing in memory when searching the classpath", but I do not know how to do this. I assumed that the options parameter for getTask represents command-line flags that would be passed to the compiler if this were happening on the command line (such as "-cp .", which also does not work), but perhaps this assumption is wrong.

Answer 1

Hi Bruce,
I have a question regarding loading a jar file by the compiler to dynamically compile with a source file. I hope you can probably offer me an idea on what has been missing or wrong with the source codes I have written for my application.
I am using Eclipse compiler to dynamically compile a class. In the class, I want it to make a reference to a jar file for compilation dynamically.
Here is the source of a test class I wrote:
import javax.servlet.http.HttpServlet;
class MyServlet extends HttpServlet {
}The import statement refers to the class javax.servlet.http.HttpServlet from the jar file C:\\Program Files\\Apache Software Foundation\\Tomcat 6.0\\lib\\servlet-api.jar placed in the file system.
In the method called compileClass (shown below), I used the path of the jar file to add to the option -classpath as you suggested.
     private static CompileClassResult compileClass(Writer out, String className, String classSource) {
          try {
               JavaCompiler javac = new EclipseCompiler();
               StandardJavaFileManager sjfm = javac.getStandardFileManager(null, null, null);
               SpecialClassLoader scl = new SpecialClassLoader();
               SpecialJavaFileManager fileManager = new SpecialJavaFileManager(sjfm, scl);
               List<String> options = new ArrayList<String>();
               options.addAll(Arrays.asList("-classpath", "C:\\Program Files\\Apache Software Foundation\\Tomcat 6.0\\lib\\servlet-api.jar"));
               List<MemorySource> compilationUnits = Arrays.asList(new MemorySource(className, classSource));
               DiagnosticListener<JavaFileObject> diagnosticListener = null;
               Iterable<String> classes = null;
               if (out == null) {
                    out = new PrintWriter(System.err);
               JavaCompiler.CompilationTask compile = javac.getTask(out, fileManager, diagnosticListener, options, classes, compilationUnits);
               boolean res = compile.call();
               if (res) {
                    //Need to modify the api to return an array of two elements - one classes and other bytecodes for all classes in the same class file.
                    return CompileClassResult.newInstance(scl.findClasses(), scl.findByteCodes());
          } catch (Exception e) {
               e.printStackTrace();               
          return null;
     }I also extended the class ForwardingJavaFileManager as you suggested and have it delegated to the StandardJavaFileManager sent to the compiler mentioned in the method compileClass above. The extended class (called SpecialJavaFileManager) is as follows:
public class SpecialJavaFileManager extends ForwardingJavaFileManager<StandardJavaFileManager> {
     private SpecialClassLoader xcl;
     public SpecialJavaFileManager(StandardJavaFileManager sjfm, SpecialClassLoader xcl) {
          super(sjfm);
          System.out.println("SpecialJavaFileManager");
          this.xcl = xcl;
     public JavaFileObject getJavaFileForOutput(Location location, String name, JavaFileObject.Kind kind, FileObject sibling) throws IOException {
          System.out.println("getJavaFileForOutput");
          MemoryByteCode mbc = new MemoryByteCode(name);
          xcl.addClass(name, mbc);
          return mbc;
     public Iterable<JavaFileObject> list(JavaFileManager.Location loc, String pkg, Set kinds, boolean recurse) throws IOException {
          System.out.println("list ");
        List<JavaFileObject> result = new ArrayList<JavaFileObject>();
        for (JavaFileObject f : super.list(loc, pkg, kinds, recurse)) {
             System.out.println(f);
            result.add(f);
          return result;
}I run the application and the result shows that it didn't load the jar file into the memory as expected. From the output (below) I got, it doesn't seem to invoke the method list(...) in the class SpecialJavaFileManager.
SpecialJavaFileManager
1. ERROR in \MyServlet.java (at line 1)
     import javax.servlet.http.*;
            ^^^^^^^^^^^^^
The import javax.servlet cannot be resolved
2. ERROR in \MyServlet.java (at line 3)
     class MyServlet extends HttpServlet {
                             ^^^^^^^^^^^
HttpServlet cannot be resolved to a typeWould you please let me know what has possibly be missing or wrong?
Thanks.
Jonathan
Edited by: jonathanlam on Aug 10, 2009 6:47 PM