Apache BCEL Source Code Files are inside the Apache BCEL source package file like bcel-6.6.1-src.zip. Unzip the source package file and go to the "src/main" sub-directory, you will see source code files.

Here is the list of Java source code files of the Apache BCEL 6.6.1 in \Users\fyicenter\bcel-6.6.1\src:

⏎ org/apache/bcel/classfile/UnknownAttributeReader.java

/*
 * 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.bcel.classfile;

/**
 * Unknown (non-standard) attributes may be read via user-defined factory objects that can be registered with the
 * Attribute.addAttributeReader method. These factory objects should implement this interface.
 *
 * @see Attribute
 * @since 6.0
 */
public interface UnknownAttributeReader {

    /**
     * When this attribute reader is added via the static method Attribute.addAttributeReader, an attribute name is
     * associated with it. As the class file parser parses attributes, it will call various AttributeReaders based on the
     * name of the attributes it is constructing.
     *
     * @param nameIndex An index into the constant pool, indexing a ConstantUtf8 that represents the name of the attribute.
     * @param length The length of the data contained in the attribute. This is written into the constant pool and should
     *        agree with what the factory expects the length to be.
     * @param file This is the data input that the factory needs to read its data from.
     * @param constantPool This is the constant pool associated with the Attribute that we are constructing.
     *
     * @return The user-defined AttributeReader should take this data and use it to construct an attribute. In the case of
     *         errors, a null can be returned which will cause the parsing of the class file to fail.
     *
     * @see Attribute#addAttributeReader(String, UnknownAttributeReader)
     */
    Attribute createAttribute(int nameIndex, int length, java.io.DataInput file, ConstantPool constantPool);
}

⏎ org/apache/bcel/classfile/UnknownAttributeReader.java

Or download all of them as a single archive file:

File name: bcel-6.6.1-sources.jar
File size: 688374 bytes
Release date: 2022-09-18
Download 

⇒ Install Apache BCEL 6.5.0 Binary Package

⇐ Download and Install Apache BCEL Source Package

⇑ Apache BCEL (Byte Code Engineering Library)

⇑⇑ Java Bytecode Tools