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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,
* 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.tomcat.util.bcel.classfile;
import java.io.DataInput;
import java.io.IOException;
import org.apache.tomcat.util.bcel.Const;
/**
* This class represents the constant pool, i.e., a table of constants, of a parsed classfile. It may contain null references, due to the JVM specification that
* skips an entry after an 8-byte constant (double, long) entry. Those interested in generating constant pools programmatically should see
* <a href="../generic/ConstantPoolGen.html"> ConstantPoolGen</a>.
*
* @see Constant
*/
public class ConstantPool {
private final Constant[] constantPool;
/**
* Reads constants from given input stream.
*
* @param input Input stream
* @throws IOException if an I/O error occurs reading the the InputStream
* @throws ClassFormatException If the .class file is not valid
*/
ConstantPool(final DataInput input) throws IOException, ClassFormatException {
final int constantPoolCount = input.readUnsignedShort();
constantPool = new Constant[constantPoolCount];
/*
* constantPool[0] is unused by the compiler and may be used freely by the implementation.
*/
for (int i = 1; i < constantPoolCount; i++) {
constantPool[i] = Constant.readConstant(input);
/*
* Quote from the JVM specification: "All eight byte constants take up two spots in the constant pool. If this is the n'th byte in the constant
* pool, then the next item will be numbered n+2"
*
* Thus we have to increment the index counter.
*/
if (constantPool[i] != null) {
byte tag = constantPool[i].getTag();
if (tag == Const.CONSTANT_Double || tag == Const.CONSTANT_Long) {
i++;
}
}
}
}
/**
* Gets constant from constant pool.
*
* @param <T> A {@link Constant} subclass
* @param index Index in constant pool
* @return Constant value
* @see Constant
* @throws ClassFormatException if index is invalid
*/
@SuppressWarnings("unchecked")
public <T extends Constant> T getConstant(final int index) throws ClassFormatException {
return (T) getConstant(index, Constant.class);
}
/**
* Gets constant from constant pool and check whether it has the expected type.
*
* @param <T> A {@link Constant} subclass
* @param index Index in constant pool
* @param tag Tag of expected constant, i.e., its type
* @return Constant value
* @see Constant
* @throws ClassFormatException if constant type does not match tag
*/
public <T extends Constant> T getConstant(final int index, final byte tag) throws ClassFormatException {
final T c = getConstant(index);
if (c.getTag() != tag) {
throw new ClassFormatException("Expected class '" + Const.getConstantName(tag) + "' at index " + index + " and got " + c);
}
return c;
}
/**
* Gets constant from constant pool.
*
* @param <T> A {@link Constant} subclass
* @param index Index in constant pool
* @param castTo The {@link Constant} subclass to cast to.
* @return Constant value
* @see Constant
* @throws ClassFormatException if index is invalid
*/
public <T extends Constant> T getConstant(final int index, final Class<T> castTo) throws ClassFormatException {
if (index >= constantPool.length || index < 0) {
throw new ClassFormatException("Invalid constant pool reference using index: " + index + ". Constant pool size is: " + constantPool.length);
}
if (constantPool[index] != null && !castTo.isAssignableFrom(constantPool[index].getClass())) {
throw new ClassFormatException("Invalid constant pool reference at index: " + index +
". Expected " + castTo + " but was " + constantPool[index].getClass());
}
// Previous check ensures this won't throw a ClassCastException
final T c = castTo.cast(constantPool[index]);
// the 0th element is always null
if (c == null && index != 0) {
final Constant prev = constantPool[index - 1];
if (prev == null || prev.getTag() != Const.CONSTANT_Double && prev.getTag() != Const.CONSTANT_Long) {
throw new ClassFormatException("Constant pool at index " + index + " is null.");
}
}
return c;
}
/**
* Gets constant from constant pool and check whether it has the expected type.
*
* @param index Index in constant pool
* @return ConstantInteger value
* @see ConstantInteger
* @throws ClassFormatException if constant type does not match tag
*/
public ConstantInteger getConstantInteger(final int index) {
return getConstant(index, Const.CONSTANT_Integer);
}
/**
* Gets constant from constant pool and check whether it has the expected type.
*
* @param index Index in constant pool
* @return ConstantUtf8 value
* @see ConstantUtf8
* @throws ClassFormatException if constant type does not match tag
*/
public ConstantUtf8 getConstantUtf8(final int index) throws ClassFormatException {
return getConstant(index, Const.CONSTANT_Utf8);
}
}
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