netconf/netconf-netty-util/src/main/java/org/opendaylight/netconf/nettyutil/handler/ThreadLocalTransformers.java

   1 /*
   2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
   3  *
   4  * This program and the accompanying materials are made available under the
   5  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   6  * and is available at http://www.eclipse.org/legal/epl-v10.html
   7  */
   8 package org.opendaylight.netconf.nettyutil.handler;
   9
  10 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
  11 import javax.xml.transform.OutputKeys;
  12 import javax.xml.transform.Transformer;
  13 import javax.xml.transform.TransformerConfigurationException;
  14 import javax.xml.transform.TransformerFactory;
  15 import javax.xml.transform.TransformerFactoryConfigurationError;
  16
  17 /**
  18  * Utility class for cached thread-local transformers. This class exists mostly for use by handlers.
  19  */
  20 final class ThreadLocalTransformers {
  21     private static final TransformerFactory FACTORY = TransformerFactory.newInstance();
  22
  23     private static final ThreadLocal<Transformer> DEFAULT_TRANSFORMER = new ThreadLocal<Transformer>() {
  24         @Override
  25         protected Transformer initialValue() {
  26             return createTransformer();
  27         }
  28
  29         @Override
  30         public void set(final Transformer value) {
  31             throw new UnsupportedOperationException();
  32         }
  33     };
  34
  35     private static final ThreadLocal<Transformer> PRETTY_TRANSFORMER = new ThreadLocal<Transformer>() {
  36         @Override
  37         protected Transformer initialValue() {
  38             final Transformer ret = createTransformer();
  39             ret.setOutputProperty(OutputKeys.INDENT, "yes");
  40             ret.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no");
  41             return ret;
  42         }
  43
  44         @Override
  45         public void set(final Transformer value) {
  46             throw new UnsupportedOperationException();
  47         }
  48     };
  49
  50     private ThreadLocalTransformers() {
  51         throw new UnsupportedOperationException("Utility class");
  52     }
  53
  54     /**
  55      * Get the transformer with default configuration.
  56      *
  57      * @return A transformer with default configuration based on the default implementation.
  58      */
  59     static Transformer getDefaultTransformer() {
  60         return DEFAULT_TRANSFORMER.get();
  61     }
  62
  63     /**
  64      * Get the transformer with default configuration, but with automatic indentation
  65      * and the XML declaration removed.
  66      *
  67      * @return A transformer with human-friendly configuration.
  68      */
  69     static Transformer getPrettyTransformer() {
  70         return PRETTY_TRANSFORMER.get();
  71     }
  72
  73     @SuppressFBWarnings(value = "UPM_UNCALLED_PRIVATE_METHOD",
  74             justification = "https://github.com/spotbugs/spotbugs/issues/811")
  75     private static Transformer createTransformer() {
  76         try {
  77             return FACTORY.newTransformer();
  78         } catch (TransformerConfigurationException | TransformerFactoryConfigurationError e) {
  79             throw new IllegalStateException("Unexpected error while instantiating a Transformer", e);
  80         }
  81     }
  82 }