How to read the full name of the .class file

Question

Hey, I think the name sums it up, but still.

I need to extract the full name of an object from its compiled .class file, can anyone point me in the right direction

Thanks,
Adam.

Answer 1

getClass().getName() 

Update: You can load the class file in byte[] (using standard I / O) and then use getClass().getClassLoader().defineClass(...)

Answer 2

 public String getFullClassName(String classFileName) throws IOException { File file = new File(classFileName); FileChannel roChannel = new RandomAccessFile(file, "r").getChannel(); ByteBuffer bb = roChannel.map(FileChannel.MapMode.READ_ONLY, 0, (int)roChannel.size()); Class<?> clazz = defineClass((String)null, bb, (ProtectionDomain)null); return clazz.getName(); } 

Answer 3

Use a library such as BCEL to read the class file in memory and request it for the class name.

Answer 4

You can read this by parsing the binary. The class file format is defined in the VM specification .

Take a look at DataInputStream if you are new to binary parsing.

Answer 5

Depending on which IDE you are using, a mechanism may arise for this. For example, in eclipse you can go to the .class file and right-click on it and select "copy full name".

Older versions of eclipse may not have this feature, but I used this plugin before:

http://www.jave.de/eclipse/copyfully/index.html

It works almost the same. Hope this helps.

Answer 6

You can look, for example, in AnnotationScanner from the JSF implementation, they load classes manually (to avoid pollution in space) to find JSF annotations. In particular, look at this:

  /** * This class is encapsulating binary .class file information as defined at * http://java.sun.com/docs/books/vmspec/2nd-edition/html/ClassFile.doc.html * <p/> * This is used by the annotation frameworks to quickly scan .class files * for the presence of annotations. This avoid the annotation framework * having to load each .class file in the class loader. * <p/> * Taken from the GlassFish V2 source base. */ @SuppressWarnings({"UnusedDeclaration"}) private static final class ClassFile { private static final int magic = 0xCAFEBABE; public static final int ACC_PUBLIC = 0x1; public static final int ACC_PRIVATE = 0x2; public static final int ACC_PROTECTED = 0x4; public static final int ACC_STATIC = 0x8; public static final int ACC_FINAL = 0x10; public static final int ACC_SYNCHRONIZED = 0x20; public static final int ACC_THREADSAFE = 0x40; public static final int ACC_TRANSIENT = 0x80; public static final int ACC_NATIVE = 0x100; public static final int ACC_INTERFACE = 0x200; public static final int ACC_ABSTRACT = 0x400; public short majorVersion; public short minorVersion; public ConstantPoolInfo constantPool[]; public short accessFlags; public ConstantPoolInfo thisClass; public ConstantPoolInfo superClass; public ConstantPoolInfo interfaces[]; /** * bunch of stuff I really don't care too much for now. * <p/> * FieldInfo fields[]; MethodInfo methods[]; * AttributeInfo attributes[]; */ ByteBuffer header; ConstantPoolInfo constantPoolInfo = new ConstantPoolInfo(); // ------------------------------------------------------------ Constructors /** * Creates a new instance of ClassFile */ public ClassFile() { header = ByteBuffer.allocate(12000); } // ---------------------------------------------------------- Public Methods public void setConstantPoolInfo(ConstantPoolInfo poolInfo) { constantPoolInfo = poolInfo; } /** * Read the input channel and initialize instance data structure. * * @param in a <code>ReadableByteChannel</code> that provides the bytes * of the classfile * * @return <code>true</code> if the bytes representing this classfile include * one of the annotations we're looking for. * * @throws IOException if an I/O error occurs while reading the class */ public boolean containsAnnotation(ReadableByteChannel in) throws IOException { /** * this is the .class file layout * ClassFile { u4 magic; u2 minor_version; u2 major_version; u2 constant_pool_count; cp_info constant_pool[constant_pool_count-1]; u2 access_flags; u2 this_class; u2 super_class; u2 interfaces_count; u2 interfaces[interfaces_count]; u2 fields_count; field_info fields[fields_count]; u2 methods_count; method_info methods[methods_count]; u2 attributes_count; attribute_info attributes[attributes_count]; } **/ header.clear(); long read = (long) in.read(header); if (read == -1) { return false; } header.rewind(); if (header.getInt() != magic) { return false; } minorVersion = header.getShort(); majorVersion = header.getShort(); int constantPoolSize = header.getShort(); return constantPoolInfo .containsAnnotation(constantPoolSize, header, in); } } // END ClassFile