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/*
* Copyright 2000,2002,2004 Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package org.apache.tools.ant.taskdefs.optional.jlink;
import java.io.DataInput;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
/**
* Reads just enough of a class file to determine the class' full name.
*
* <p>Extremely minimal constant pool implementation, mainly to support extracting
* strings from a class file.
* @author <a href="mailto:beard@netscape.com">Patrick C. Beard</a>.
*/
class ConstantPool {
static final
byte UTF8 = 1, UNUSED = 2, INTEGER = 3, FLOAT = 4, LONG = 5, DOUBLE = 6,
CLASS = 7, STRING = 8, FIELDREF = 9, METHODREF = 10,
INTERFACEMETHODREF = 11, NAMEANDTYPE = 12;
byte[] types;
Object[] values;
ConstantPool(DataInput data) throws IOException {
super();
int count = data.readUnsignedShort();
types = new byte [ count ];
values = new Object [ count ];
// read in all constant pool entries.
for (int i = 1; i < count; i++) {
byte type = data.readByte();
types[i] = type;
switch (type) {
case UTF8 :
values[i] = data.readUTF();
break;
case UNUSED :
break;
case INTEGER :
values[i] = new Integer(data.readInt());
break;
case FLOAT :
values[i] = new Float(data.readFloat());
break;
case LONG :
values[i] = new Long(data.readLong());
++i;
break;
case DOUBLE :
values[i] = new Double(data.readDouble());
++i;
break;
case CLASS :
case STRING :
values[i] = new Integer(data.readUnsignedShort());
break;
case FIELDREF :
case METHODREF :
case INTERFACEMETHODREF :
case NAMEANDTYPE :
values[i] = new Integer(data.readInt());
break;
}
}
}
}
/**
* Provides a quick and dirty way to determine the true name of a class
* given just an InputStream. Reads in just enough to perform this
* minimal task only.
*/
public class ClassNameReader extends Object {
public static String getClassName(InputStream input) throws IOException {
DataInputStream data = new DataInputStream(input);
// verify this is a valid class file.
int cookie = data.readInt();
if (cookie != 0xCAFEBABE) {
return null;
}
/* int version = */ data.readInt();
// read the constant pool.
ConstantPool constants = new ConstantPool(data);
Object[] values = constants.values;
// read access flags and class index.
/* int accessFlags = */ data.readUnsignedShort();
int classIndex = data.readUnsignedShort();
Integer stringIndex = (Integer) values[classIndex];
String className = (String) values[stringIndex.intValue()];
return className;
}
}
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