问读取和显示Java .class版本的工具

EN

public static void main(String[] args) throws IOException {
    var files = Arrays.stream(args).map(Path::of).collect(Collectors.toList());
    ShowClassVersions v = new ShowClassVersions();
    for (var f : files) {
        v.scan(f);
    }
    v.print();
}

Version: 49.0 ~ JDK-5
   C:\jars\junit-platform-console-standalone-1.7.1.jar
Version: 50.0 ~ JDK-6
   C:\jars\junit-platform-console-standalone-1.7.1.jar
Version: 52.0 ~ JDK-8
   C:\java\apache-tomcat-10.0.12\lib\catalina.jar
   C:\jars\junit-platform-console-standalone-1.7.1.jar
Version: 53.0 ~ JDK-9
   C:\java\apache-tomcat-10.0.12\lib\catalina.jar
   C:\jars\junit-platform-console-standalone-1.7.1.jar

public class ShowClassVersions {
    private TreeMap<String, ArrayList<String>> vers = new TreeMap<>();
    private static final byte[] CLASS_MAGIC = new byte[] { (byte) 0xca, (byte) 0xfe, (byte) 0xba, (byte) 0xbe };
    private final byte[] bytes = new byte[8];

    private String versionOfClass(InputStream in) throws IOException  {
        int c = in.readNBytes(bytes, 0, bytes.length);
        if (c == bytes.length && Arrays.mismatch(bytes, CLASS_MAGIC) == CLASS_MAGIC.length) {
            int minorVersion = (bytes[4] << 8) + (bytes[4] << 0);
            int majorVersion = (bytes[6] << 8) + (bytes[7] << 0);
            return ""+ majorVersion + "." + minorVersion;
        }
        return "Unknown";
    }

    private Matcher classes = Pattern.compile("\\.(class|ear|war|jar)$").matcher("");

    // This code scans any path (dir or file):
    public void scan(Path f) throws IOException {
        try (var stream = Files.find(f, Integer.MAX_VALUE,
                (p, a) -> a.isRegularFile() && classes.reset(p.toString()).find())) {
            stream.forEach(this::scanFile);
        }
    }

    private void scanFile(Path f) {
        String fn = f.getFileName().toString();
        try {
            if (fn.endsWith(".ear") || fn.endsWith(".war") || fn.endsWith(".jar"))
                scanArchive(f);
            else if (fn.endsWith(".class"))
                store(f.toAbsolutePath().toString(), versionOfClass(f));
        } catch (IOException e) {
            throw new UncheckedIOException(e);
        }
    }

    private void scanArchive(Path p) throws IOException {
        try (InputStream in = Files.newInputStream(p)) {
            scanArchive(p.toAbsolutePath().toString(), Files.newInputStream(p));
        }
    }

    private void scanArchive(String desc, InputStream in) throws IOException {
        HashSet<String> versions = new HashSet<>();
        ZipInputStream zip = new ZipInputStream(in);
        for (ZipEntry entry = null; (entry = zip.getNextEntry()) != null; ) {
            String name = entry.getName();
            // There could be different compiler versions per class in one jar
            if (name.endsWith(".class")) {
                versions.add(versionOfClass(zip));
            } else if (name.endsWith(".jar") || name.endsWith(".war")) {
                scanArchive(desc + " => " + name, zip);
            }
        }
        if (versions.size() > 1)
            System.out.println("Warn: "+desc+" contains multiple versions: "+versions);

        for (String version : versions)
            store(desc, version);
    }

    private String versionOfClass(Path p) throws IOException {
        try (InputStream in = Files.newInputStream(p)) {
            return versionOfClass(in);
        }
    }

    private void store(String path, String jdkVer) {
        vers.computeIfAbsent(jdkVer, k -> new ArrayList<>()).add(path);
    }

    // Could add a mapping table for JDK names, this guesses based on (JDK17 = 61.0)
    public void print() {
        for (var ver : vers.keySet()) {
            System.out.println("Version: " + ver + " ~ " +jdkOf(ver));
            for (var p : vers.get(ver)) {
                System.out.println("   " + p);
            }
        }
    }

    private static String jdkOf(String ver)  {
        try {
            return "JDK-"+((int)Float.parseFloat(ver)-44);
        }
        catch(NumberFormatException nfe)
        {
            return "JDK-??";
        }
    }
}