基于Java的高性能系统设计源码解析与优化技巧：新书《高性能Java系统权威指南》2022年12月出版

package com.ibeetl.code.core.om.asm; import java.util.List; import com.ibeetl.code.core.om.AttributeAccess; import org.objectweb.asm.ClassWriter; import org.objectweb.asm.Label; import org.objectweb.asm.MethodVisitor; import org.objectweb.asm.Opcodes; /** * 通过ASM生成{@link AttributeAccess}的子类， * 假设类名称User，则为生成的类为：User$AttributeAccess * 实现 {@link AttributeAccess#value(Object, Object)}方法。 *<p/> * <h3>Bean中没有get(String)或get(Object)方法:</h3> * <pre> public Object value(Object bean, Object attr) { String attrStr = attr.toString(); int hash = attrStr.hashCode(); User user = (User) bean; switch (hash) { case 1: return user.getName(); case 2: return user.getAddress(); case 3: if("numbers".equals(attrStr)){ return user.getNumbers(); } if("birthDate".equals(attrStr)){ return user.getBirthDate(); } } throw new BeetlException(BeetlException.ATTRIBUTE_NOT_FOUND, "attribute : " + attrStr); } *</pre> * <h3>Bean中有get(String)方法:</h3> * <pre> public Object value(Object bean, Object attr) { String attrStr = attr.toString(); int hash = attrStr.hashCode(); User user = (User) bean; switch (hash) { case 1: return user.getName(); case 2: return user.getAddress(); case 3: if("numbers".equals(attrStr)){ return user.getNumbers(); } if("birthDate".equals(attrStr)){ return user.getBirthDate(); } } return user.get(attrStr); } *</pre> *</pre> * <h3>Bean中有get(Object)方法:</h3> * <pre> public Object value(Object bean, Object attr) { String attrStr = attr.toString(); int hash = attrStr.hashCode(); User user = (User) bean; switch (hash) { case 1: return user.getName(); case 2: return user.getAddress(); case 3: if("numbers".equals(attrStr)){ return user.getNumbers(); } if("birthDate".equals(attrStr)){ return user.getBirthDate(); } } return user.get(attr); } *</pre> * @author laozhaishaozuo@foxmail.com * */ class EnhanceClassGenerator implements Opcodes { /** * 实例方法this变量位置 */ private static final int VAR_THIS_INDEX = 0; /** * 方法中第一个参数的位置 */ private static final int VAR_BEAN_INDEX = 1; /** * 方法中第二个参数的位置 */ private static final int VAR_ATTR_INDEX = 2; /** * 本地变量对应attrName的toString变量 */ private static final int LOCAL_VAR_ATTR_STRING_INDEX = 3; /** * 本地变量hashCode位置 */ private static final int LOCAL_VAR_HASH_CODE_INDEX = 4; /** * 本地变量innerClass类型变量的位置 */ private static final int LOCAL_VAR_INTERNAL_CLASS_INDEX = 5; private EnhanceClassGenerator() { } /** * 生成beanClass对应的增强类的字节流 * * @param beanClass * @return * @throws Exception */ static byte[] generate(Class<?> beanClass) throws Exception { return generate(beanClass, true); } /** * 生成beanClass对应的增强类的字节流 * * @param beanClass * @param usePropertyDescriptor * 是否使{@link java.beans.PropertyDescriptor}来生成属性描述 * @return * @throws Exception */ static byte[] generate(Class<?> beanClass, boolean usePropertyDescriptor) throws Exception { return generate(beanClass, BeanEnhanceConstants.SUPER_CLASS_NAME, null, usePropertyDescriptor); } /** * 生成beanClass对应的增强类的字节流 * * @param beanClass * @param superName * 父类 形式如 java.lang.String * @param interfaces * 要实现的接口 形式如 java.lang.String * @return * @throws Exception */ static byte[] generate(Class<?> beanClass, String superName, String[] interfaces, boolean usePropertyDescriptor) throws Exception { String beanClassName = beanClass.getName(); ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);// 自动计算maxStack String getterClassName = createGeneratedClassName(beanClassName); cw.visit(V1_8, ACC_PUBLIC + ACC_SUPER, BeanEnhanceUtils.getInternalName(getterClassName), null, superName, interfaces); // 生成默认构造函数 generateDefaultConstruct(cw, superName); // 生成GetterClass generateMethod(cw, beanClass, usePropertyDescriptor); cw.visitEnd(); return cw.toByteArray(); } /** * 生成默认的构造方法 * * @param cw * @param superName 父类名称 */ static void generateDefaultConstruct(ClassWriter cw, String superName) { MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null); // 生成构造方法的字节码指令 mv.visitVarInsn(ALOAD, 0); mv.visitMethodInsn(INVOKESPECIAL, superName, "<init>", "()V", false); mv.visitInsn(RETURN); mv.visitMaxs(1, 1); mv.visitEnd(); } static String createGeneratedClassName(String className) { return className + "$" + BeanEnhanceConstants.GENETRATED_CLASS_SUFFIX; } static String createGeneratedClassName(Class<?> beanClass) { return createGeneratedClassName(beanClass.getName()); } /** * 生成方法 方法 * * @param cw * @param beanClass * @param usePropertyDescriptor * @See {@link AttributeAccess#value(Object, Object)} */ private static void generateMethod(ClassWriter cw, Class<?> beanClass, boolean usePropertyDescriptor) { String internalClassName = BeanEnhanceUtils.getInternalName(beanClass.getName()); ClassDescription classDescription = BeanEnhanceUtils.getClassDescription(beanClass, usePropertyDescriptor); MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, BeanEnhanceConstants.METHOD_TO_GENERATE, BeanEnhanceConstants.METHOD_SIGNATURE, null, null); mv.visitCode(); // 有属性，需要调用getter方法 if (classDescription.hasField) { generateMethodWithFileds(internalClassName, classDescription, mv); } else { generateMethodWithNoFiled(mv, classDescription, internalClassName); } mv.visitEnd(); } private static void generateMethodWithFileds(String internalClassName, ClassDescription classDescription, MethodVisitor mv) { Label toStringLabel = new Label(); mv.visitLabel(toStringLabel); mv.visitVarInsn(ALOAD, VAR_ATTR_INDEX); mv.visitMethodInsn(INVOKEVIRTUAL, BeanEnhanceConstants.OBJECT_INTERNAL_NAME, BeanEnhanceConstants.TO_STRING_METHOD_NAME, BeanEnhanceConstants.TO_STRING_METHOD_DESCRIPTOR, false); mv.visitVarInsn(ASTORE, LOCAL_VAR_ATTR_STRING_INDEX);// 对应attrName的toString变量 Label hashCodeLabel = new Label(); mv.visitLabel(hashCodeLabel); mv.visitVarInsn(ALOAD, LOCAL_VAR_ATTR_STRING_INDEX);// toString变量 mv.visitMethodInsn(INVOKEVIRTUAL, BeanEnhanceConstants.OBJECT_INTERNAL_NAME, "hashCode", "()I", false); mv.visitVarInsn(ISTORE, LOCAL_VAR_HASH_CODE_INDEX);// hashCode Label castLabel = new Label(); mv.visitLabel(castLabel); mv.visitVarInsn(ALOAD, VAR_BEAN_INDEX);// 参数 bean mv.visitTypeInsn(CHECKCAST, internalClassName); mv.visitVarInsn(ASTORE, LOCAL_VAR_INTERNAL_CLASS_INDEX);// 对应internalClassName类型的变量 Label l2 = new Label(); mv.visitLabel(l2); mv.visitVarInsn(ILOAD, LOCAL_VAR_HASH_CODE_INDEX); Label[] lookupSwitchLabels = new Label[classDescription.fieldDescMap.size()]; int[] hashCodes = BeanEnhanceUtils .convertIntegerToPrimitiveType(classDescription.fieldDescMap.keySet().toArray(new Integer[1])); for (int i = 0; i < lookupSwitchLabels.length; i++) { lookupSwitchLabels[i] = new Label(); } Label df = new Label(); mv.visitLookupSwitchInsn(df, hashCodes, lookupSwitchLabels); List<FieldDescription> fieldDescs = null; FieldDescription curFieldDesc = null; for (int i = 0; i