Where Can I get source code files of jsse.jar?

You can get source code files of jsse.jar (JSSE) from OpenJDK GitHub Website in the src/share/classes/sun/security/ssl/ directory.

You can also browse JSSE Source Code files below:

⏎ sun/security/ssl/Debug.java

/*
 * Copyright (c) 1999, 2010, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.security.ssl;

import java.io.PrintStream;
import java.security.AccessController;
import java.util.Locale;

import sun.security.action.GetPropertyAction;

/**
 * This class has be shamefully lifted from sun.security.util.Debug
 *
 * @author Gary Ellison
 */
public class Debug {

    private String prefix;

    private static String args;

    static {
        args = java.security.AccessController.doPrivileged(
            new GetPropertyAction("javax.net.debug", ""));
        args = args.toLowerCase(Locale.ENGLISH);
        if (args.equals("help")) {
            Help();
        }
    }

    public static void Help()
    {
        System.err.println();
        System.err.println("all            turn on all debugging");
        System.err.println("ssl            turn on ssl debugging");
        System.err.println();
        System.err.println("The following can be used with ssl:");
        System.err.println("\trecord       enable per-record tracing");
        System.err.println("\thandshake    print each handshake message");
        System.err.println("\tkeygen       print key generation data");
        System.err.println("\tsession      print session activity");
        System.err.println("\tdefaultctx   print default SSL initialization");
        System.err.println("\tsslctx       print SSLContext tracing");
        System.err.println("\tsessioncache print session cache tracing");
        System.err.println("\tkeymanager   print key manager tracing");
        System.err.println("\ttrustmanager print trust manager tracing");
        System.err.println("\tpluggability print pluggability tracing");
        System.err.println();
        System.err.println("\thandshake debugging can be widened with:");
        System.err.println("\tdata         hex dump of each handshake message");
        System.err.println("\tverbose      verbose handshake message printing");
        System.err.println();
        System.err.println("\trecord debugging can be widened with:");
        System.err.println("\tplaintext    hex dump of record plaintext");
        System.err.println("\tpacket       print raw SSL/TLS packets");
        System.err.println();
        System.exit(0);
    }

    /**
     * Get a Debug object corresponding to whether or not the given
     * option is set. Set the prefix to be the same as option.
     */

    public static Debug getInstance(String option)
    {
        return getInstance(option, option);
    }

    /**
     * Get a Debug object corresponding to whether or not the given
     * option is set. Set the prefix to be prefix.
     */
    public static Debug getInstance(String option, String prefix)
    {
        if (isOn(option)) {
            Debug d = new Debug();
            d.prefix = prefix;
            return d;
        } else {
            return null;
        }
    }

    /**
     * True if the property "javax.net.debug" contains the
     * string "option".
     */
    public static boolean isOn(String option)
    {
        if (args == null) {
            return false;
        } else {
            int n = 0;
            option = option.toLowerCase(Locale.ENGLISH);

            if (args.indexOf("all") != -1) {
                return true;
            } else if ((n = args.indexOf("ssl")) != -1) {
                if (args.indexOf("sslctx", n) == -1) {
                    // don't enable data and plaintext options by default
                    if (!(option.equals("data")
                        || option.equals("packet")
                        || option.equals("plaintext"))) {
                        return true;
                    }
                }
            }
            return (args.indexOf(option) != -1);
        }
    }

    /**
     * print a message to stderr that is prefixed with the prefix
     * created from the call to getInstance.
     */

    public void println(String message)
    {
        System.err.println(prefix + ": "+message);
    }

    /**
     * print a blank line to stderr that is prefixed with the prefix.
     */

    public void println()
    {
        System.err.println(prefix + ":");
    }

    /**
     * print a message to stderr that is prefixed with the prefix.
     */

    public static void println(String prefix, String message)
    {
        System.err.println(prefix + ": "+message);
    }

    public static void println(PrintStream s, String name, byte[] data) {
        s.print(name + ":  { ");
        if (data == null) {
            s.print("null");
        } else {
            for (int i = 0; i < data.length; i++) {
                if (i != 0) s.print(", ");
                s.print(data[i] & 0x0ff);
            }
        }
        s.println(" }");
    }

    /**
     * Return the value of the boolean System property propName.
     *
     * Note use of doPrivileged(). Do make accessible to applications.
     */
    static boolean getBooleanProperty(String propName, boolean defaultValue) {
        // if set, require value of either true or false
        String b = AccessController.doPrivileged(
                new GetPropertyAction(propName));
        if (b == null) {
            return defaultValue;
        } else if (b.equalsIgnoreCase("false")) {
            return false;
        } else if (b.equalsIgnoreCase("true")) {
            return true;
        } else {
            throw new RuntimeException("Value of " + propName
                + " must either be 'true' or 'false'");
        }
    }

    static String toString(byte[] b) {
        return sun.security.util.Debug.toString(b);
    }
}

⏎ sun/security/ssl/Debug.java

Or download all of them as a single archive file:

File name: sun-security-ssl-openjdk7u-fyi.zip
File size: 277845 bytes
Release date: 2012-05-03
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