org.apache.tomcat.util.bcel.classfile.Constant Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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,
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* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package org.apache.tomcat.util.bcel.classfile;
import java.io.DataInput;
import java.io.IOException;
import org.apache.tomcat.util.bcel.Const;
/**
* Abstract superclass for classes to represent the different constant types
* in the constant pool of a class file. The classes keep closely to
* the JVM specification.
*
* @author M. Dahm
*/
public abstract class Constant {
/* In fact this tag is redundant since we can distinguish different
* `Constant' objects by their type, i.e., via `instanceof'. In some
* places we will use the tag for switch()es anyway.
*
* First, we want match the specification as closely as possible. Second we
* need the tag as an index to select the corresponding class name from the
* `CONSTANT_NAMES' array.
*/
protected final byte tag;
Constant(final byte tag) {
this.tag = tag;
}
/**
* @return Tag of constant, i.e., its type. No setTag() method to avoid
* confusion.
*/
public final byte getTag() {
return tag;
}
/**
* Read one constant from the given input, the type depends on a tag byte.
*
* @param dataInput Input stream
* @return Constant object
* @throws IOException if an I/O error occurs reading from the given {@code dataInput}.
* @throws ClassFormatException if the next byte is not recognized
*/
static Constant readConstant(final DataInput dataInput) throws IOException, ClassFormatException {
final byte b = dataInput.readByte(); // Read tag byte
int skipSize;
switch (b) {
case Const.CONSTANT_Class:
return new ConstantClass(dataInput);
case Const.CONSTANT_Integer:
return new ConstantInteger(dataInput);
case Const.CONSTANT_Float:
return new ConstantFloat(dataInput);
case Const.CONSTANT_Long:
return new ConstantLong(dataInput);
case Const.CONSTANT_Double:
return new ConstantDouble(dataInput);
case Const.CONSTANT_Utf8:
return ConstantUtf8.getInstance(dataInput);
case Const.CONSTANT_String:
case Const.CONSTANT_MethodType:
case Const.CONSTANT_Module:
case Const.CONSTANT_Package:
skipSize = 2; // unsigned short
break;
case Const.CONSTANT_MethodHandle:
skipSize = 3; // unsigned byte, unsigned short
break;
case Const.CONSTANT_Fieldref:
case Const.CONSTANT_Methodref:
case Const.CONSTANT_InterfaceMethodref:
case Const.CONSTANT_NameAndType:
case Const.CONSTANT_Dynamic:
case Const.CONSTANT_InvokeDynamic:
skipSize = 4; // unsigned short, unsigned short
break;
default:
throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
}
Utility.skipFully(dataInput, skipSize);
return null;
}
@Override
public String toString() {
return "[" + tag + "]";
}
}