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/fo/expr/Function.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: Function.java 1330317 2012-04-25 14:48:09Z gadams $ */

package org.apache.fop.fo.expr;

import org.apache.fop.datatypes.PercentBase;
import org.apache.fop.fo.properties.Property;

/**
 * Interface for managing XSL-FO Functions
 */
public interface Function {

    /**
     * @return the number of required (non-optional) arguments that must be specified
     * in the argument list
     */
    int getRequiredArgsCount();

    /**
     * @return the number of non-required (optional) arguments that may be specified
     * in the argument list, which, if specified, must follow the required arguments
     */
    int getOptionalArgsCount();

    /**
     * @param index of optional argument
     * @param pi property information instance that applies to property being evaluated
     * @return the default property value for the optional argument at INDEX, where
     * INDEX is with respect to optional arguments; i.e., the first optional argument
     * position is index 0; if no default for a given index, then null is returned
     * @throws PropertyException if index is greater than or equal to optional args count
     */
    Property getOptionalArgDefault(int index, PropertyInfo pi) throws PropertyException;

    /**
     * Determine if function allows variable arguments. If it does, then they must appear
     * after required and optional arguments, and all optional arguments must be specified.
     * @return true if function permits additional variable number of arguments after
     * required and (completely specified) optional arguments
     */
    boolean hasVariableArgs();

    /**
     * @return the basis for percentage calculations
     */
    PercentBase getPercentBase();

    /**
     * Evaluate the function
     * @param args an array of Properties that should be evaluated
     * @param pi property information instance that applies to property being evaluated
     * @return the Property satisfying the function
     * @throws PropertyException for problems when evaluating the function
     */
    Property eval(Property[] args, PropertyInfo pi) throws PropertyException;

}

⏎ org/apache/fop/fo/expr/Function.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)