org.apache.drill.exec.compile

Class ClassBuilder

java.lang.Object

org.apache.drill.exec.compile.ClassBuilder

public class ClassBuilder
extends Object

Implements the "plain Java" method of code generation and compilation. Given a CodeGenerator, obtains the generated source code, compiles it with the selected compiler, loads the byte-codes into a class loader and provides the resulting class. Compared with the ClassTransformer mechanism, this one requires the code generator to have generated a complete Java class that is capable of direct compilation and loading. This means the generated class must be a subclass of the template so that the JVM can use normal Java inheritance to associate the template and generated methods.

Here is how to use the plain Java technique to debug generated code:

• Set the config option drill.exec.compile.code_dir to the location where you want to save the generated source code.
• Where you generate code (using a CodeGenerator), set the "plain Java" options:

   CodeGenerator<Foo> cg = ...
   cg.plainJavaCapable(true); // Class supports plain Java
   cg.preferPlainJava(true); // Actually generate plain Java
   cg.saveCodeForDebugging(true); // Save code for debugging
   ...

  Note that saveCodeForDebugging automatically sets the PJ option if the generator is capable. Call preferPlainJava only if you want to try PJ for this particular generated class without saving the generated code.
• In your favorite IDE, add to the code lookup path the code directory saved earlier. In Eclipse, for example, you do this in the debug configuration you will use to debug Drill.
• Set a breakpoint in template used for the generated code.
• Run Drill. The IDE will stop at your breakpoint.
• Step into the generated code. Examine class field and local variables. Have fun!

Most generated classes have been upgraded to support Plain Java compilation. Once this work is complete, the calls to plainJavaCapable can be removed as all generated classes will be capable.

The setting to prefer plain Java is ignored for any remaining generated classes not marked as plain Java capable.

Field Summary

Fields

Modifier and Type	Field and Description
static String	CODE_DIR_OPTION

Constructor Summary

Constructors

Constructor and Description
ClassBuilder(DrillConfig config, OptionSet optionManager)

Method Summary

Methods

Modifier and Type	Method and Description
Class<?>	getImplementationClass(CodeGenerator<?> cg) Given a code generator which has already generated plain Java code, compile the code, create a class loader, and return the resulting Java class.

Methods inherited from class java.lang.Object

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

Field Detail

CODE_DIR_OPTION

public static final String CODE_DIR_OPTION

See Also:

Constant Field Values

Constructor Detail

ClassBuilder

public ClassBuilder(DrillConfig config,
            OptionSet optionManager)

Method Detail

getImplementationClass

public Class<?> getImplementationClass(CodeGenerator<?> cg)
                                throws ClassTransformationException

Given a code generator which has already generated plain Java code, compile the code, create a class loader, and return the resulting Java class.

Parameters:

cg - a plain Java capable code generator that has generated plain Java code

Returns:

the class that the code generator defines

Throws:

ClassTransformationException