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Venice, a sandboxed Lisp implemented in Java.
There is a newer version: 1.12.34
/*   __    __         _
 *   \ \  / /__ _ __ (_) ___ ___
 *    \ \/ / _ \ '_ \| |/ __/ _ \
 *     \  /  __/ | | | | (_|  __/
 *      \/ \___|_| |_|_|\___\___|
 *
 *
 * Copyright 2017-2024 Venice
 *
 * Licensed 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 com.github.jlangch.venice.impl.javainterop;

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

import com.github.jlangch.venice.impl.util.io.ClassPathResource;


/**
 * Reads the Java major version from a class file
 *
 * The definition of the class file format can be found here:
 * Format
 *
 * 

 *  Java 1.2 uses major version 46
 *  Java 1.3 uses major version 47
 *  Java 1.4 uses major version 48
 *  Java 5 uses major version 49
 *  Java 6 uses major version 50
 *  Java 7 uses major version 51
 *  Java 8 uses major version 52
 *  Java 9 uses major version 53
 *  Java 10 uses major version 54
 *  Java 11 uses major version 55
 *  Java 12 uses major version 56
 *  Java 13 uses major version 57
 *  Java 14 uses major version 58
 *  Java 15 uses major version 59
 * 
 */
public class ClassVersionChecker {

    public static int getClassResourceMajorVersion(final String classResource) {
        try {
            return readMajorVersion(
                        new ClassPathResource(classResource).getInputStream(),
                        classResource);
        }
        catch(IOException ex) {
            throw new RuntimeException(
                    "Failed to retrieve Java major version for class "
                        + "resource '" + classResource + "'!");
        }
    }

    public static int getClassFileMajorVersion(final String filename) {
        try {
            return readMajorVersion(
                        new FileInputStream(filename),
                        filename);
        }
        catch(IOException ex) {
            throw new RuntimeException(
                    "Failed to retrieve Java major version for file"
                        + " '" + filename + "'!");
        }
    }

    @SuppressWarnings("unused")
    private static int readMajorVersion(final InputStream in, final String source) throws IOException {
        try (DataInputStream din = new DataInputStream(in)) {

            final int magic = din.readInt();
            if (magic != MAGIC) {
                throw new RuntimeException(source + " is not a valid class!");
            }

            final int minor = din.readUnsignedShort();
            final int major = din.readUnsignedShort();

            return major;
        }
    }


    private static int MAGIC = 0xcafebabe; // 4 bytes
}