Java tutorial
/* * This file is part of SpongeAPI, licensed under the MIT License (MIT). * * Copyright (c) SpongePowered <https://www.spongepowered.org> * Copyright (c) contributors * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. */ package org.spongepowered.api.util.generator.dummy; import static com.google.common.base.Preconditions.checkNotNull; import static com.google.common.base.Preconditions.checkState; import static org.objectweb.asm.Opcodes.AASTORE; import static org.objectweb.asm.Opcodes.ACC_PUBLIC; import static org.objectweb.asm.Opcodes.ACC_SUPER; import static org.objectweb.asm.Opcodes.ALOAD; import static org.objectweb.asm.Opcodes.ANEWARRAY; import static org.objectweb.asm.Opcodes.ATHROW; import static org.objectweb.asm.Opcodes.DUP; import static org.objectweb.asm.Opcodes.GETFIELD; import static org.objectweb.asm.Opcodes.INVOKESPECIAL; import static org.objectweb.asm.Opcodes.INVOKESTATIC; import static org.objectweb.asm.Opcodes.NEW; import static org.objectweb.asm.Opcodes.PUTFIELD; import static org.objectweb.asm.Opcodes.RETURN; import static org.objectweb.asm.Opcodes.V1_8; import org.objectweb.asm.ClassWriter; import org.objectweb.asm.MethodVisitor; import org.objectweb.asm.Opcodes; import org.objectweb.asm.Type; import java.lang.reflect.Method; import java.lang.reflect.Modifier; import java.util.ArrayList; import java.util.List; public class DummyClassGenerator { private static final String FIELD_NAME = "fieldName"; public byte[] createClass(final Class<?> type, final String name, final Class<?> exceptionType) { checkNotNull(type, "type"); checkNotNull(name, "name"); checkNotNull(exceptionType, "exception"); checkState(type.isInterface(), String.format("Class %s is not an interface!", type)); checkState(Throwable.class.isAssignableFrom(exceptionType), String.format("Class %s does not extend Throwable!", exceptionType)); String internalName = name.replace('.', '/'); List<Method> methods = this.getInterfaceMethods(type); ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES); cw.visit(V1_8, ACC_PUBLIC + ACC_SUPER, internalName, null, Type.getInternalName(Object.class), new String[] { Type.getInternalName(type) }); this.generateConstructor(cw, internalName); this.generateMethods(cw, internalName, methods, exceptionType); cw.visitEnd(); return cw.toByteArray(); } private void generateConstructor(ClassWriter cw, String internalName) { cw.visitField(Modifier.PRIVATE, FIELD_NAME, Type.getDescriptor(String.class), null, null); MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, "<init>", "(Ljava/lang/String;)V", null, null); // Load 'this' mv.visitVarInsn(ALOAD, 0); // Cal super() mv.visitMethodInsn(INVOKESPECIAL, Type.getInternalName(Object.class), "<init>", "()V", false); // Load 'this' mv.visitVarInsn(ALOAD, 0); // Load first method parameter (the fieldName) mv.visitVarInsn(ALOAD, 1); // Store first parameter in field FIELD_NAME mv.visitFieldInsn(PUTFIELD, internalName, FIELD_NAME, Type.getDescriptor(String.class)); mv.visitInsn(RETURN); mv.visitMaxs(0, 0); mv.visitEnd(); } private void generateMethods(ClassWriter cw, String internalName, List<Method> methods, Class<?> exceptionType) { for (Method method : methods) { MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, method.getName(), Type.getMethodDescriptor(method), null, null); mv.visitCode(); String internalException = Type.getInternalName(exceptionType); mv.visitTypeInsn(NEW, internalException); mv.visitInsn(DUP); // Load first argument to String.format mv.visitLdcInsn( "A method was invoked on a dummy class, due to the static field %s not being initialized " + "(most likely in a CatalogType-related class).\n" + "Method: " + method); // Create new array mv.visitLdcInsn(1); mv.visitTypeInsn(ANEWARRAY, "java/lang/String"); // Store in local var 2 mv.visitVarInsn(Opcodes.ASTORE, 2); // AASTORE part 1 - array reference mv.visitVarInsn(Opcodes.ALOAD, 2); // AASTORE part 2 - array index mv.visitLdcInsn(0); // AASTORE part 3 = the actual value // Load formatter argument (the field FIELD_NAME) mv.visitVarInsn(ALOAD, 0); mv.visitFieldInsn(GETFIELD, internalName, FIELD_NAME, Type.getDescriptor(String.class)); // Store in array mv.visitInsn(AASTORE); // Load array reference mv.visitVarInsn(ALOAD, 2); // Call String.format mv.visitMethodInsn(INVOKESTATIC, Type.getInternalName(String.class), "format", "(Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/String;", false); // Invoke throwable constructor mv.visitMethodInsn(INVOKESPECIAL, internalException, "<init>", "(Ljava/lang/String;)V", false); mv.visitInsn(ATHROW); mv.visitMaxs(0, 0); mv.visitEnd(); } } private List<Method> getInterfaceMethods(Class<?> clazz) { List<Method> methods = new ArrayList<>(); Method[] allMethods = clazz.getMethods(); for (Method method : allMethods) { if (!Modifier.isStatic(method.getModifiers())) { methods.add(method); } } return methods; } }