使用ASM库修改字节码后,无法加载类。
这是身份转换器,我希望得到的修改数组的大小与字节1相同,但要短2倍!(439和278)
String path = SimpleClass.class.getName().replace(".", "/") + ".class"; ClassLoader classLoader = SimpleClass.class.getClassLoader(); InputStream is = classLoader.getResourceAsStream(path); byte[] bytes = IOUtils.toByteArray(is); ClassReader reader = new ClassReader(bytes); ClassWriter writer = new ClassWriter(reader, 0); byte[] modified = writer.toByteArray();
加载失败没有什么奇妙的。我怀疑标头被截断了,但是两个数组中的第一个字节都相同。
-54,-2,-70
static class ByteClassLoader extends ClassLoader { public Class define(String name, byte[] body) { return defineClass(name, body, 0, body.length); } } ByteClassLoader myLoader = new ByteClassLoader(); Class myClass = myLoader.define("Ooo", modified);
失败并出现错误:
java.lang.UnsupportedClassVersionError: Ooo has been compiled by a more recent version of the Java Runtime (class file version 0.0), this version of the Java Runtime only recognizes class file versions up to 52.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:763) at java.lang.ClassLoader.defineClass(ClassLoader.java:642) at PrintTest$ByteClassLoader.define(PrintTest.java:24) at PrintTest.x(PrintTest.java:48) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.junit.runner.JUnitCore.run(JUnitCore.java:137) at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:117) at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:42) at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:253) at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:84)
这些字节对应于0xcafeba与Java类文件幻数匹配的字节0xcafebabe。
0xcafeba
0xcafebabe
这里的问题是,new ClassWriter(reader, 0)您无法做到自己想像的那样。请参阅API文档:
new ClassWriter(reader, 0)
classReader-用于读取原始类的ClassReader。它将用于从原始类复制整个常量池,并在适用的情况下复制原始字节码的其他片段。
classReader
我们实际上仍然需要作者通过来 访问 读者ClassReader.accept,如下所示:
ClassReader.accept
reader.accept(writer, 0);
附带说明一下,您不需要IOUtils.toByteArary像那样ClassReader的构造函数InputStream。
IOUtils.toByteArary
ClassReader
InputStream