我正在使用 ASM Java 库来替换一些反射。我生成了这个方法的主体:
void set(Object object, int fieldIndex, Object value);
使用这个生成的方法,我可以在运行时在对象上设置字段,而无需使用反射。它很好用。但是,我发现原始字段失败了。这是我的设置方法的相关部分:
for (int i = 0, n = cachedFields.length; i < n; i++) {
mv.visitLabel(labels[i]);
mv.visitFrame(Opcodes.F_SAME, 0, null, 0, null);
mv.visitVarInsn(ALOAD, 1);
mv.visitTypeInsn(CHECKCAST, targetClassName);
mv.visitVarInsn(ALOAD, 3);
Field field = cachedFields[i].field;
Type fieldType = Type.getType(field.getType());
mv.visitFieldInsn(PUTFIELD, targetClassName, field.getName(), fieldType.getDescriptor());
mv.visitInsn(RETURN);
}
此代码正在为选择生成案例标签。它适用于对象,但对于基元,我收到此错误:
Expecting to find float on stack
好的,有道理,我需要自己拆箱。我实现了以下内容:
for (int i = 0, n = cachedFields.length; i < n; i++) {
mv.visitLabel(labels[i]);
mv.visitFrame(Opcodes.F_SAME, 0, null, 0, null);
mv.visitVarInsn(ALOAD, 1);
mv.visitTypeInsn(CHECKCAST, targetClassName);
mv.visitVarInsn(ALOAD, 3);
Field field = cachedFields[i].field;
Type fieldType = Type.getType(field.getType());
switch (fieldType.getSort()) {
case Type.BOOLEAN:
mv.visitTypeInsn(CHECKCAST, "java/lang/Boolean");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Boolean", "booleanValue", "()Z");
break;
case Type.BYTE:
mv.visitTypeInsn(CHECKCAST, "java/lang/Byte");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Byte", "byteValue", "()B");
break;
case Type.CHAR:
mv.visitTypeInsn(CHECKCAST, "java/lang/Character");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Character", "charValue", "()C");
break;
case Type.SHORT:
mv.visitTypeInsn(CHECKCAST, "java/lang/Short");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Short", "shortValue", "()S");
break;
case Type.INT:
mv.visitTypeInsn(CHECKCAST, "java/lang/Integer");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Integer", "intValue", "()I");
break;
case Type.FLOAT:
mv.visitTypeInsn(CHECKCAST, "java/lang/Float");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Float", "floatValue", "()F");
break;
case Type.LONG:
mv.visitTypeInsn(CHECKCAST, "java/lang/Long");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Long", "longValue", "()J");
break;
case Type.DOUBLE:
mv.visitTypeInsn(CHECKCAST, "java/lang/Double");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Double", "doubleValue", "()D");
break;
case Type.ARRAY:
mv.visitTypeInsn(CHECKCAST, fieldType.getDescriptor());
break;
case Type.OBJECT:
mv.visitTypeInsn(CHECKCAST, fieldType.getInternalName());
break;
}
mv.visitFieldInsn(PUTFIELD, targetClassName, field.getName(), fieldType.getDescriptor());
mv.visitInsn(RETURN);
}
我已经追查过了,它确实进入了相应字段的“case Type.FLOAT”,但是,我得到了这个错误:
Expecting to find object/array on stack
这就是我卡住的地方。对于我的生活,我无法弄清楚为什么拆箱不起作用。 “ALOAD, 3”是将set方法的第三个参数压入栈中,应该是一个Float。有什么想法吗?
我发现 asm-commons 库有一个 GeneratorAdapter 类,它有一个 unbox 方法。但是,我真的不想为应该如此简单的东西包含另一个 JAR。我查看了 GeneratorAdapter 源代码,它正在做一些非常相似的事情。我尝试修改我的代码以使用 GeneratorAdapter,只是为了看看它是否有效,但发现它根本不容易转换。
最佳答案
原来上面的拆箱工作正常。在尝试将结果作为对象返回之前,我有代码正在执行获取而不是装箱结果。没有更简单的测试是我的错!
如果其他人需要它,这里是正确的装箱代码:
Type fieldType = Type.getType(...);
switch (fieldType.getSort()) {
case Type.BOOLEAN:
mv.visitMethodInsn(INVOKESTATIC, "java/lang/Boolean", "valueOf", "(Z)Ljava/lang/Boolean;");
break;
case Type.BYTE:
mv.visitMethodInsn(INVOKESTATIC, "java/lang/Byte", "valueOf", "(B)Ljava/lang/Byte;");
break;
case Type.CHAR:
mv.visitMethodInsn(INVOKESTATIC, "java/lang/Character", "valueOf", "(C)Ljava/lang/Character;");
break;
case Type.SHORT:
mv.visitMethodInsn(INVOKESTATIC, "java/lang/Short", "valueOf", "(S)Ljava/lang/Short;");
break;
case Type.INT:
mv.visitMethodInsn(INVOKESTATIC, "java/lang/Integer", "valueOf", "(I)Ljava/lang/Integer;");
break;
case Type.FLOAT:
mv.visitMethodInsn(INVOKESTATIC, "java/lang/Float", "valueOf", "(F)Ljava/lang/Float;");
break;
case Type.LONG:
mv.visitMethodInsn(INVOKESTATIC, "java/lang/Long", "valueOf", "(J)Ljava/lang/Long;");
break;
case Type.DOUBLE:
mv.visitMethodInsn(INVOKESTATIC, "java/lang/Double", "valueOf", "(D)Ljava/lang/Double;");
break;
}
关于java - 使用 ASM Java 库拆箱,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/1566185/