Class CompilingClassLoader

java.lang.Object

java.lang.ClassLoader

com.google.common.truth.codegen.CompilingClassLoader

@GwtIncompatible("java.lang.reflect.*")
public class CompilingClassLoader
extends ClassLoader

This is a Java ClassLoader that will attempt to load a class from a string of source code.

Example

String className = "com.foo.MyClass";
String classSource =
  "package com.foo;\n" +
  "public class MyClass implements Runnable {\n" +
  "  @Override public void run() {\n" +
  "   log(\"Hello world\");\n" +
  "  }\n" +
  "}";

// Load class from source.
ClassLoader classLoader = new CompilingClassLoader(
    parentClassLoader, className, classSource);
Class myClass = classLoader.loadClass(className);

// Use it.
Runnable instance = (Runnable)myClass.newInstance();
instance.run();

Only one chunk of source can be compiled per instance of CompilingClassLoader. If you need to compile more, create multiple CompilingClassLoader instances. Uses Java 1.6's in built compiler API. If the class cannot be compiled, loadClass() will throw a ClassNotFoundException and log the compile errors to System.err. If you don't want the messages logged, or want to explicitly handle the messages you can provide your own DiagnosticListener through {#setDiagnosticListener()}.

See Also:

• ClassLoader
• JavaCompiler

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	CompilingClassLoader.CompilerException	Thrown when code cannot be compiled.
private class	CompilingClassLoader.InMemoryFileManager	Provides an in-memory representation of JavaFileManager abstraction, so we do not need to write any files to disk.
private static class	CompilingClassLoader.InMemoryJavaFile

Field Summary

Fields

Modifier and Type	Field	Description
private final Map<String, ByteArrayOutputStream>	byteCodeForClasses
private static final URI	EMPTY_URI

Constructor Summary

Constructors

Constructor	Description
CompilingClassLoader(ClassLoader parent, String className, String sourceCode, DiagnosticListener<JavaFileObject> diagnosticListener)

Method Summary

Modifier and Type	Method	Description
private boolean	compileSourceCodeToByteCode(String className, String sourceCode, DiagnosticListener<JavaFileObject> diagnosticListener)
Class<?>	findClass(String name)	Override ClassLoader's class resolving method.

Methods inherited from class ClassLoader

clearAssertionStatus, defineClass, defineClass, defineClass, defineClass, definePackage, findLibrary, findLoadedClass, findResource, findResources, findSystemClass, getClassLoadingLock, getPackage, getPackages, getParent, getResource, getResourceAsStream, getResources, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources, loadClass, loadClass, registerAsParallelCapable, resolveClass, setClassAssertionStatus, setDefaultAssertionStatus, setPackageAssertionStatus, setSigners

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

byteCodeForClasses

private final Map<String, ByteArrayOutputStream> byteCodeForClasses

EMPTY_URI

private static final URI EMPTY_URI

Constructor Details

CompilingClassLoader

public CompilingClassLoader(ClassLoader parent,
 String className,
 String sourceCode,
 DiagnosticListener<JavaFileObject> diagnosticListener)
                     throws CompilingClassLoader.CompilerException

Parameters:

parent - Parent classloader to resolve dependencies from.

className - Name of class to compile. eg. "com.foo.MyClass".

sourceCode - Java source for class. e.g. "package com.foo; class MyClass { ... }".

diagnosticListener - Notified of compiler errors (may be null).

Throws:

CompilingClassLoader.CompilerException

Method Details

findClass

public Class<?> findClass(String name)
                   throws ClassNotFoundException

Override ClassLoader's class resolving method. Don't call this directly, instead use ClassLoader.loadClass(String).

Overrides:

findClass in class ClassLoader

Throws:

ClassNotFoundException

compileSourceCodeToByteCode

private boolean compileSourceCodeToByteCode(String className,
 String sourceCode,
 DiagnosticListener<JavaFileObject> diagnosticListener)

Returns:

Whether compilation was successful.