聊聊java的java.security.egd

    // name of the *System* property, takes precedence over PROP_RNDSOURCE
    private final static String PROP_EGD = "java.security.egd";
    // name of the *Security* property
    private final static String PROP_RNDSOURCE = "securerandom.source";

    final static String URL_DEV_RANDOM = "file:/dev/random";
    final static String URL_DEV_URANDOM = "file:/dev/urandom";

    private static final String seedSource;

    static {
        seedSource = AccessController.doPrivileged(
                new PrivilegedAction<String>() {

            @Override
            public String run() {
                String egdSource = System.getProperty(PROP_EGD, "");
                if (egdSource.length() != 0) {
                    return egdSource;
                }
                egdSource = Security.getProperty(PROP_RNDSOURCE);
                if (egdSource == null) {
                    return "";
                }
                return egdSource;
            }
        });
    }

    // Static initializer to hook in selected or best performing generator
    static {
        String egdSource = SunEntries.getSeedSource();

        /*
         * Try the URL specifying the source (e.g. file:/dev/random)
         *
         * The URLs "file:/dev/random" or "file:/dev/urandom" are used to
         * indicate the SeedGenerator should use OS support, if available.
         *
         * On Windows, this causes the MS CryptoAPI seeder to be used.
         *
         * On Solaris/Linux/MacOS, this is identical to using
         * URLSeedGenerator to read from /dev/[u]random
         */
        if (egdSource.equals(SunEntries.URL_DEV_RANDOM) ||
                egdSource.equals(SunEntries.URL_DEV_URANDOM)) {
            try {
                instance = new NativeSeedGenerator(egdSource);
                if (debug != null) {
                    debug.println(
                        "Using operating system seed generator" + egdSource);
                }
            } catch (IOException e) {
                if (debug != null) {
                    debug.println("Failed to use operating system seed "
                                  + "generator: " + e.toString());
                }
            }
        } else if (egdSource.length() != 0) {
            try {
                instance = new URLSeedGenerator(egdSource);
                if (debug != null) {
                    debug.println("Using URL seed generator reading from "
                                  + egdSource);
                }
            } catch (IOException e) {
                if (debug != null) {
                    debug.println("Failed to create seed generator with "
                                  + egdSource + ": " + e.toString());
                }
            }
        }

        // Fall back to ThreadedSeedGenerator
        if (instance == null) {
            if (debug != null) {
                debug.println("Using default threaded seed generator");
            }
            instance = new ThreadedSeedGenerator();
        }
    }

/**
 * Native seed generator for Unix systems. Inherit everything from
 * URLSeedGenerator.
 *
 */
class NativeSeedGenerator extends SeedGenerator.URLSeedGenerator {

    NativeSeedGenerator(String seedFile) throws IOException {
        super(seedFile);
    }

}

public final class NativePRNG extends SecureRandomSpi {

    private static final long serialVersionUID = -6599091113397072932L;

    private static final Debug debug = Debug.getInstance("provider");

    // name of the pure random file (also used for setSeed())
    private static final String NAME_RANDOM = "/dev/random";
    // name of the pseudo random file
    private static final String NAME_URANDOM = "/dev/urandom";

    // which kind of RandomIO object are we creating?
    private enum Variant {
        MIXED, BLOCKING, NONBLOCKING
    }

    // singleton instance or null if not available
    private static final RandomIO INSTANCE = initIO(Variant.MIXED);

    /**
     * Get the System egd source (if defined).  We only allow "file:"
     * URLs for now. If there is a egd value, parse it.
     *
     * @return the URL or null if not available.
     */
    private static URL getEgdUrl() {
        // This will return "" if nothing was set.
        String egdSource = SunEntries.getSeedSource();
        URL egdUrl;

        if (egdSource.length() != 0) {
            if (debug != null) {
                debug.println("NativePRNG egdUrl: " + egdSource);
            }
            try {
                egdUrl = new URL(egdSource);
                if (!egdUrl.getProtocol().equalsIgnoreCase("file")) {
                    return null;
                }
            } catch (MalformedURLException e) {
                return null;
            }
        } else {
            egdUrl = null;
        }

        return egdUrl;
    }

    //......
}