MarkerField.java

package com.avaje.ebean.enhance.agent;

import com.avaje.ebean.enhance.asm.ClassVisitor;
import com.avaje.ebean.enhance.asm.FieldVisitor;
import com.avaje.ebean.enhance.asm.Label;
import com.avaje.ebean.enhance.asm.MethodVisitor;
import com.avaje.ebean.enhance.asm.Opcodes;

/**
 * Used to detect if a class has been enhanced.
 * <p>
 * Moved to use this over just relying on the existence of the EntityBean interface
 * to make the enhancement more robust.
 * </p>
 */
public class MarkerField implements Opcodes, EnhanceConstants {

	/**
	 * The name of the static field added. Its value is the class being enhanced.
	 */
	public static final String _EBEAN_MARKER = "_EBEAN_MARKER";
	
	/**
	 * Add the _EBEAN_MARKER field.
	 */
	public static String addField(ClassVisitor cv, String className) {

		String cn = className.replace('/', '.');
		
		FieldVisitor fv = cv.visitField(ACC_PRIVATE + ACC_STATIC, _EBEAN_MARKER, "Ljava/lang/String;", null, cn);
		fv.visitEnd();
		
		return cn;
	}

	/**
	 * Generate the _ebean_getMarker() method.
	 * 
	 * <pre>
	 * public String _ebean_getMarker() {
	 * 	return _EBEAN_MARKER;
	 * }
	 * </pre>
	 */
	public static void addGetMarker(ClassVisitor cv, String className) {
		
		
		MethodVisitor mv;
		
		mv = cv.visitMethod(ACC_PUBLIC, "_ebean_getMarker", "()Ljava/lang/String;", null, null);
		mv.visitCode();
		Label l0 = new Label();
		mv.visitLabel(l0);
		mv.visitLineNumber(1, l0);
		mv.visitFieldInsn(GETSTATIC, className, "_EBEAN_MARKER", "Ljava/lang/String;");
		mv.visitInsn(ARETURN);
		Label l1 = new Label();
		mv.visitLabel(l1);
		mv.visitLocalVariable("this", "L"+className+";", null, l0, l1, 0);
		mv.visitMaxs(1, 1);
		mv.visitEnd();
	}
}