1

因此，这是我尝试使用 ASM 的类验证器验证的字节码片段：

public <init>(Ljava/io/InputStream;)V
    ALOAD 0
    ALOAD 1
    SIPUSH 2048
    NEW org/apache/xerces/impl/msg/XMLMessageFormatter
    DUP
    INVOKESPECIAL org/apache/xerces/impl/msg/XMLMessageFormatter.<init> ()V
    INVOKESTATIC java/util/Locale.getDefault ()Ljava/util/Locale;
    INVOKESPECIAL org/apache/xerces/impl/io/UTF8Reader.<init> (Ljava/io/InputStream;ILorg/apache/xerces/util/MessageFormatter;Ljava/util/Locale;)V
    RETURN
    MAXSTACK = 5
    MAXLOCALS = 2

这是一个更大的类 org/apache/xerces/impl/io/UTF8Reader 的一部分。现在，当我通过 ASM 提供的 Class verifier 运行这个类的字节码时，我得到以下结果：

org.objectweb.asm.tree.analysis.AnalyzerException: **Error at instruction 7: java.lang.ClassNotFoundException: org.apache.xerces.util.MessageFormatter**
    at org.objectweb.asm.tree.analysis.Analyzer.analyze(Unknown Source)
    at org.objectweb.asm.util.CheckClassAdapter.verify(Unknown Source)
    at org.objectweb.asm.util.CheckClassAdapter.verify(Unknown Source)
    at org.objectweb.asm.util.CheckClassAdapter.main(Unknown Source)
Caused by: java.lang.RuntimeException: java.lang.ClassNotFoundException: org.apache.xerces.util.MessageFormatter
    at org.objectweb.asm.tree.analysis.SimpleVerifier.getClass(Unknown Source)
    at org.objectweb.asm.tree.analysis.SimpleVerifier.isAssignableFrom(Unknown Source)
    at org.objectweb.asm.tree.analysis.SimpleVerifier.isSubTypeOf(Unknown Source)
    at org.objectweb.asm.tree.analysis.BasicVerifier.naryOperation(Unknown Source)
    at org.objectweb.asm.tree.analysis.BasicVerifier.naryOperation(Unknown Source)
    at org.objectweb.asm.tree.analysis.Frame.execute(Unknown Source)
    ... 4 more
<init>(Ljava/io/InputStream;)V
00000 UTF8Reader InputStream  :  :     ALOAD 0
00001 UTF8Reader InputStream  : UTF8Reader  :     ALOAD 1
00002 UTF8Reader InputStream  : UTF8Reader InputStream  :     SIPUSH 2048
00003 UTF8Reader InputStream  : UTF8Reader InputStream I  :     NEW org/apache/xerces/impl/msg/XMLMessageFormatter
00004 UTF8Reader InputStream  : UTF8Reader InputStream I XMLMessageFormatter  :     DUP
00005 UTF8Reader InputStream  : UTF8Reader InputStream I XMLMessageFormatter XMLMessageFormatter  :     INVOKESPECIAL org/apache/xerces/impl/msg/XMLMessageFormatter.<init> ()V
00006 UTF8Reader InputStream  : UTF8Reader InputStream I XMLMessageFormatter  :     INVOKESTATIC java/util/Locale.getDefault ()Ljava/util/Locale;
00007 UTF8Reader InputStream  : UTF8Reader InputStream I XMLMessageFormatter Locale  :     INVOKESPECIAL org/apache/xerces/impl/io/UTF8Reader.<init> (Ljava/io/InputStream;ILorg/apache/xerces/util/MessageFormatter;Ljava/util/Locale;)V
00008 ?        :     RETURN

我对最后一点感到非常困惑......为什么它在第 7 行为 org/apache/xerces/util/MessageFormatter 对象发出 ClassNotFound 异常？

谢谢。

4

1 回答 1

1

ASM 的验证器工具会根据 JVM 规范检查每个堆栈和变量槽的有效性。其中一项检查是所有变量和堆栈槽中的值在合并点具有相同的类型。因此，此实现加载类以查找常见的超类型。

于 2012-07-10T13:49:04.343 回答