Example usage for java.lang.invoke MethodHandle bindTo

Introduction

In this page you can find the example usage for java.lang.invoke MethodHandle bindTo.

Prototype

public MethodHandle bindTo(Object x) 

Source Link

Document

Binds a value x to the first argument of a method handle, without invoking it.

Usage

From source file:de.zib.sfs.WrappedFSDataInputStream.java

/**
 * Gets the datanode that was last read from as a string. Should be called
 * after the first read operation has been performed.
 * //w  w w .ja  va 2 s.c om
 * @return "->" + hostname of the datanode, or empty string if the
 *         information is not available
 */
private String getDatanodeHostNameString() {
    if (this.datanodeHostnameSupplier == null) {
        if (this.in instanceof HdfsDataInputStream) {
            // call Hadoop's method directly
            final HdfsDataInputStream hdfsIn = (HdfsDataInputStream) this.in;
            if (hdfsIn.getCurrentDatanode() != null) {
                this.datanodeHostnameSupplier = () -> hdfsIn.getCurrentDatanode().getHostName();
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Using datanodeHostNameSupplier from Hadoop.");
                }
            } else {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("datanodeHostNameSupplier from Hadoop has no DataNode information.");
                }
                this.datanodeHostnameSupplier = () -> "";
            }
        } else {
            try {
                // Check if there's an appropriately named method available
                // that returns the hostname of the current node that is
                // being read from. Using the lambda factory provides almost
                // direct invocation performance.
                MethodHandles.Lookup methodHandlesLookup = MethodHandles.lookup();

                // try this stream or the one it wraps
                Method getCurrentDatanodeHostNameMethod = null;
                InputStream bindToStream = null;
                try {
                    getCurrentDatanodeHostNameMethod = this.in.getClass()
                            .getDeclaredMethod("getCurrentDatanodeHostName");
                    bindToStream = this.in;
                } catch (NoSuchMethodException e) {
                    getCurrentDatanodeHostNameMethod = this.in.getWrappedStream().getClass()
                            .getDeclaredMethod("getCurrentDatanodeHostName");
                    bindToStream = this.in.getWrappedStream();
                }

                MethodHandle datanodeHostNameSupplierTarget = LambdaMetafactory.metafactory(methodHandlesLookup,
                        "get", MethodType.methodType(Supplier.class, bindToStream.getClass()),
                        MethodType.methodType(Object.class),
                        methodHandlesLookup.unreflect(getCurrentDatanodeHostNameMethod),
                        MethodType.methodType(Object.class)).getTarget();
                this.datanodeHostnameSupplier = (Supplier<String>) datanodeHostNameSupplierTarget
                        .bindTo(bindToStream).invoke();

                if (LOG.isDebugEnabled()) {
                    LOG.debug("Using 'getCurrentDatanodeHostName' as datanodeHostNameSupplier.");
                }
            } catch (Throwable t) {
                this.datanodeHostnameSupplier = () -> "";
                if (LOG.isDebugEnabled()) {
                    LOG.debug("No datanodeHostNameSupplier available.", t);
                }
            }
        }
    }

    // handle cases where we have to perform a reverse lookup if
    // hostname is an IP
    String dnHostname = this.datanodeHostnameSupplier.get();
    String cachedHostname = HOSTNAME_CACHE.get(dnHostname);
    if (cachedHostname == null) {
        try {
            // strip port if necessary
            int portIndex = dnHostname.indexOf(":");
            cachedHostname = InetAddress
                    .getByName(portIndex == -1 ? dnHostname : dnHostname.substring(0, portIndex)).getHostName();
        } catch (UnknownHostException e) {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Could not determine hostname for " + dnHostname, e);
            }
            cachedHostname = "";
        }
        HOSTNAME_CACHE.put(dnHostname, cachedHostname);
    }
    return cachedHostname;
}

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