如何使用javassist获取常量池表

如何使用javassist从类文件中获取常量池表

我已经在这里编写了代码：

ClassPool pool = ClassPool.getDefault();
pool.insertClassPath(filepath);
CtClass cc = pool.get(filename);

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现在，请告诉我进一步的步骤。

一旦您拥有了CtClass，您只需要访问classFile对象来检索常量池，如下所示：

ClassPool pool = ClassPool.getDefault(); 
pool.insertClassPath(filepath); 
CtClass cc = pool.get(filename);
ConstPool classConstantPool = cc.getClassFile().getConstPool()

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如果有人在这里绊倒了，可以用一种更有效的方式（不使用

ClassPool

）完成：

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如果性能非常重要，可以对其进行优化，以便仅从文件中读取常量池：

try (InputStream inputStream = Files.newInputStream(Paths.get(filepath))) {
  return readConstantPool(new DataInputStream(inputStream));
}

其中：

// copied from ClassFile#read(DataInputStream)
private static ConstPool readConstantPool(@NonNull DataInputStream in) throws IOException {
  int magic = in.readInt();
  if (magic != 0xCAFEBABE) {
    throw new IOException("bad magic number: " + Integer.toHexString(magic));
  }

  int minor = in.readUnsignedShort();
  int major = in.readUnsignedShort();
  return new ConstPool(in);
}

// copied from ClassFile#read(DataInputStream)
private static ConstPool readConstantPool(@NonNull DataInputStream in) throws IOException {
  int magic = in.readInt();
  if (magic != 0xCAFEBABE) {
    throw new IOException("bad magic number: " + Integer.toHexString(magic));
  }

  int minor = in.readUnsignedShort();
  int major = in.readUnsignedShort();
  return new ConstPool(in);
}