What Is fop.jar? I got it from the fop-2.7-bin.zip.

fop.jar in fop-2.7-bin.zip is the JAR file for FOP 2.7, which is a print formatter driven by XSL formatting objects (XSL-FO). You can obtain fop.jar from the build folder of the fop-2.7-bin.zip file.

Below is the information about the fop.jar (2.2) file:

JAR File Size and Download Location:

JAR name: fop.jar, fop-2.7.jar
Target JDK version: 1.7
File name: fop.jar
File size: 4442817 bytes
Release date: 20-Jan-2022
Download: Apache FOP Website

Java source code files for fop.jar:

⏎ org/apache/fop/pdf/ObjectStreamManager.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.
 */

/* $Id: ObjectStreamManager.java 1305467 2012-03-26 17:39:20Z vhennebert $ */

package org.apache.fop.pdf;

import java.util.ArrayList;
import java.util.List;

import org.apache.fop.pdf.xref.CompressedObjectReference;

/**
 * Manages a collection of object streams, creating new streams as necessary to keep the
 * number of objects in each stream at the recommended value. Streams are related to each
 * other through the use of the Extends entry in the stream dictionary.
 */
class ObjectStreamManager {

    private static final int OBJECT_STREAM_CAPACITY = 100;

    private final PDFDocument pdfDocument;

    private final List<CompressedObjectReference> compressedObjectReferences;

    private int numObjectsInStream;

    private ObjectStream currentObjectStream;

    ObjectStreamManager(PDFDocument pdfDocument) {
        this.pdfDocument = pdfDocument;
        createObjectStream();
        compressedObjectReferences = new ArrayList<CompressedObjectReference>();
    }

    void add(CompressedObject compressedObject) {
        if (numObjectsInStream++ == OBJECT_STREAM_CAPACITY) {
            createObjectStream();
            numObjectsInStream = 1;
        }
        compressedObjectReferences.add(currentObjectStream.addObject(compressedObject));
    }

    private void createObjectStream() {
        currentObjectStream = currentObjectStream == null
                ? new ObjectStream()
                : new ObjectStream(currentObjectStream);
        pdfDocument.assignObjectNumber(currentObjectStream);
        pdfDocument.addTrailerObject(currentObjectStream);
    }

    List<CompressedObjectReference> getCompressedObjectReferences() {
        return compressedObjectReferences;
    }
}

⏎ org/apache/fop/pdf/ObjectStreamManager.java

Or download all of them as a single archive file:

File name: fop-2.7-src.zip
File size: 3401312 bytes
Release date: 2022-01-20
Download 

⇒ "fop" Command in fop-2.7-bin.zip

⇐ What Is fop-2.7-bin.zip

⇑ Download and Installing of FOP 2.x

⇑⇑ FAQ for FOP (Formatting Object Processor)