Java tutorial
/** * Copyright 2012 NetDigital Sweden AB * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.nginious.http.xsp.expr; import java.util.concurrent.atomic.AtomicLong; import org.objectweb.asm.ClassWriter; import org.objectweb.asm.Label; import org.objectweb.asm.MethodVisitor; import org.objectweb.asm.Opcodes; /** * Creates bytecode compiled expressions from tree value node expressions. * * @author Bojan Pisler, NetDigital Sweden AB * */ public class ExpressionCompiler { private static final AtomicLong classNameCounter = new AtomicLong(1); private String classBaseName; /** * Creates an expression compiler for * @param classBaseName */ public ExpressionCompiler(String classBaseName) { super(); this.classBaseName = classBaseName; } /** * Creates a compiled expression from the specified tree value node expression. The class bytecode for the * compiled expression is generated at runtime. * * @param uncompiled the uncompiled tree value node expression * @return the compiled expression * @throws ExpressionException if unable to compile expression */ public Expression compile(TreeExpression uncompiled) throws ExpressionException { ClassWriter writer = new ClassWriter(0); // Create class String className = classBaseName + classNameCounter.getAndIncrement(); String classIdentifier = className.replace('.', '/'); writer.visit(Opcodes.V1_6, Opcodes.ACC_PUBLIC, classIdentifier, "L" + classIdentifier + ";", "com/nginious/http/xsp/expr/Expression", null); // Create constructor MethodVisitor visitor = writer.visitMethod(Opcodes.ACC_PROTECTED, "<init>", "()V", null, null); visitor.visitCode(); visitor.visitVarInsn(Opcodes.ALOAD, 0); visitor.visitMethodInsn(Opcodes.INVOKESPECIAL, "com/nginious/http/xsp/expr/Expression", "<init>", "()V"); visitor.visitInsn(Opcodes.RETURN); visitor.visitMaxs(1, 1); visitor.visitEnd(); // protected abstract boolean evaluateBoolean(); visitor = writer.visitMethod(Opcodes.ACC_PROTECTED, "evaluateBoolean", "()Z", null, null); if (uncompiled.getType() == Type.BOOLEAN) { uncompiled.compile(visitor); } else if (uncompiled.getType() == Type.DOUBLE) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateDouble", "()D"); Label endLabel = new Label(); Label falseLabel = new Label(); visitor.visitLdcInsn(0.0d); visitor.visitInsn(Opcodes.DCMPL); visitor.visitJumpInsn(Opcodes.IFEQ, falseLabel); visitor.visitLdcInsn(true); visitor.visitJumpInsn(Opcodes.GOTO, endLabel); visitor.visitLabel(falseLabel); visitor.visitLdcInsn(false); visitor.visitLabel(endLabel); } else if (uncompiled.getType() == Type.INT) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateInt", "()I"); Label endLabel = new Label(); Label falseLabel = new Label(); visitor.visitLdcInsn(0); visitor.visitJumpInsn(Opcodes.IFNE, falseLabel); visitor.visitLdcInsn(true); visitor.visitJumpInsn(Opcodes.GOTO, endLabel); visitor.visitLabel(falseLabel); visitor.visitLdcInsn(false); visitor.visitLabel(endLabel); } else if (uncompiled.getType() == Type.STRING) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateString", "()Ljava/lang/String;"); visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Boolean", "parseBoolean", "(Ljava/lang/String;)Z"); } visitor.visitInsn(Opcodes.IRETURN); visitor.visitMaxs(5, 5); visitor.visitEnd(); // protected abstract int evaluateInt(); visitor = writer.visitMethod(Opcodes.ACC_PROTECTED, "evaluateInt", "()I", null, null); if (uncompiled.getType() == Type.BOOLEAN) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateBoolean", "()Z"); Label endLabel = new Label(); Label falseLabel = new Label(); visitor.visitJumpInsn(Opcodes.IFEQ, falseLabel); visitor.visitLdcInsn(1); visitor.visitJumpInsn(Opcodes.GOTO, endLabel); visitor.visitLabel(falseLabel); visitor.visitLdcInsn(0); visitor.visitLabel(endLabel); } else if (uncompiled.getType() == Type.DOUBLE) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateDouble", "()D"); visitor.visitInsn(Opcodes.D2I); } else if (uncompiled.getType() == Type.INT) { uncompiled.compile(visitor); } else if (uncompiled.getType() == Type.STRING) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateString", "()Ljava/lang/String;"); visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Integer", "parseInt", "(Ljava/lang/String;)I"); } visitor.visitInsn(Opcodes.IRETURN); visitor.visitMaxs(5, 5); visitor.visitEnd(); // protected abstract double evaluateDouble(); visitor = writer.visitMethod(Opcodes.ACC_PROTECTED, "evaluateDouble", "()D", null, null); if (uncompiled.getType() == Type.BOOLEAN) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateBoolean", "()Z"); Label endLabel = new Label(); Label falseLabel = new Label(); visitor.visitJumpInsn(Opcodes.IFEQ, falseLabel); visitor.visitLdcInsn(1.0d); visitor.visitJumpInsn(Opcodes.GOTO, endLabel); visitor.visitLabel(falseLabel); visitor.visitLdcInsn(0.0d); visitor.visitLabel(endLabel); } else if (uncompiled.getType() == Type.DOUBLE) { uncompiled.compile(visitor); } else if (uncompiled.getType() == Type.INT) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateInt", "()I"); visitor.visitInsn(Opcodes.I2D); } else if (uncompiled.getType() == Type.STRING) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateString", "()Ljava/lang/String;"); visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Double", "parseDouble", "(Ljava/lang/String;)D"); } visitor.visitInsn(Opcodes.DRETURN); visitor.visitMaxs(5, 5); visitor.visitEnd(); // protected abstract String evaluateString(); visitor = writer.visitMethod(Opcodes.ACC_PROTECTED, "evaluateString", "()Ljava/lang/String;", null, null); if (uncompiled.getType() == Type.BOOLEAN) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateBoolean", "()Z"); visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Boolean", "toString", "(Z)Ljava/lang/String;"); } else if (uncompiled.getType() == Type.DOUBLE) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateDouble", "()D"); visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Double", "toString", "(D)Ljava/lang/String;"); } else if (uncompiled.getType() == Type.INT) { visitor.visitVarInsn(Opcodes.ALOAD, 0); // this visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, classIdentifier, "evaluateInt", "()I"); visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Integer", "toString", "(I)Ljava/lang/String;"); } else if (uncompiled.getType() == Type.STRING) { uncompiled.compile(visitor); } visitor.visitInsn(Opcodes.ARETURN); visitor.visitMaxs(6, 6); visitor.visitEnd(); // public abstract Type getType(); visitor = writer.visitMethod(Opcodes.ACC_PUBLIC, "getType", "()Lcom/nginious/http/xsp/expr/Type;", null, null); if (uncompiled.getType() == Type.BOOLEAN) { visitor.visitFieldInsn(Opcodes.GETSTATIC, "com/nginious/http/xsp/expr/Type", "BOOLEAN", "Lcom/nginious/http/xsp/expr/Type;"); visitor.visitInsn(Opcodes.ARETURN); } else if (uncompiled.getType() == Type.DOUBLE) { visitor.visitFieldInsn(Opcodes.GETSTATIC, "com/nginious/http/xsp/expr/Type", "DOUBLE", "Lcom/nginious/http/xsp/expr/Type;"); visitor.visitInsn(Opcodes.ARETURN); } else if (uncompiled.getType() == Type.INT) { visitor.visitFieldInsn(Opcodes.GETSTATIC, "com/nginious/http/xsp/expr/Type", "INT", "Lcom/nginious/http/xsp/expr/Type;"); visitor.visitInsn(Opcodes.ARETURN); } else if (uncompiled.getType() == Type.STRING) { visitor.visitFieldInsn(Opcodes.GETSTATIC, "com/nginious/http/xsp/expr/Type", "STRING", "Lcom/nginious/http/xsp/expr/Type;"); visitor.visitInsn(Opcodes.ARETURN); } visitor.visitMaxs(1, 1); visitor.visitEnd(); try { writer.visitEnd(); byte[] clazzBytes = writer.toByteArray(); Class<?> clazz = loadClass(className, clazzBytes); return (Expression) clazz.newInstance(); } catch (Exception e) { throw new ExpressionException("Can't instantiate compiled expression", e); } } public Type test() { return Type.STRING; } /** * Loads class bytecode from the specified buffer b into a class with the specified class name. The * system class loader is used to load the class. * * @param className the class name * @param b the bytecode * @return the loaded class * @throws Exception if bytecode is invalid or a class loading error occurs */ Class<?> loadClass(String className, byte[] b) throws Exception { //override classDefine (as it is protected) and define the class. Class<?> clazz = null; ClassLoader loader = ClassLoader.getSystemClassLoader(); Class<?> cls = Class.forName("java.lang.ClassLoader"); java.lang.reflect.Method method = cls.getDeclaredMethod("defineClass", new Class[] { String.class, byte[].class, int.class, int.class }); // protected method invocaton method.setAccessible(true); try { Object[] args = new Object[] { className, b, new Integer(0), new Integer(b.length) }; clazz = (Class<?>) method.invoke(loader, args); } finally { method.setAccessible(false); } return clazz; } }