Examples of java.lang.ref.SoftReference

java.lang.ref.SoftReference
Soft reference objects, which are cleared at the discretion of the garbage collector in response to memory demand. Soft references are most often used to implement memory-sensitive caches.
Suppose that the garbage collector determines at a certain point in time that an object is softly reachable. At that time it may choose to clear atomically all soft references to that object and all soft references to any other softly-reachable objects from which that object is reachable through a chain of strong references. At the same time or at some later time it will enqueue those newly-cleared soft references that are registered with reference queues.
All soft references to softly-reachable objects are guaranteed to have been cleared before the virtual machine throws an OutOfMemoryError. Otherwise no constraints are placed upon the time at which a soft reference will be cleared or the order in which a set of such references to different objects will be cleared. Virtual machine implementations are, however, encouraged to bias against clearing recently-created or recently-used soft references.
Direct instances of this class may be used to implement simple caches; this class or derived subclasses may also be used in larger data structures to implement more sophisticated caches. As long as the referent of a soft reference is strongly reachable, that is, is actually in use, the soft reference will not be cleared. Thus a sophisticated cache can, for example, prevent its most recently used entries from being discarded by keeping strong referents to those entries, leaving the remaining entries to be discarded at the discretion of the garbage collector. @version 1.36, 02/26/09 @author Mark Reinhold @since 1.2


    // generate the tangent table used in IHStoRGB for byte type
    private synchronized void generateTanTable() {
        if ((tanSoftRef == null) || (tanSoftRef.get() == null)) {
            tanTable = new double[256] ;
            tanSoftRef = new SoftReference(tanTable);


            for (int i = 0; i < 256; i++)
                tanTable[i] = Math.tan(i * PI2 / 255.0) ;
        }
    }

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  if (softRef == null ||
            ((colorConvertOpBuf = (HashMap)softRef.get()) == null)) {


      colorConvertOpBuf = new HashMap();
      softRef = new SoftReference(colorConvertOpBuf);
  }


  ArrayList hashcode = new ArrayList(2);
  hashcode.add(0, src);
  hashcode.add(1, dst);

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      throw new NullPointerException( "Key to get cannot be null" );
    }


    clearObsoleteReferences();


    SoftReference ref = (SoftReference) softRefCache.get( key );
    if ( ref != null ) {
      Object refValue = ref.get();
      if ( refValue != null ) {
        // This ensures recently used entries are strongly-reachable
        strongRefCache.put( key, refValue );
        return refValue;
      }

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    }


    clearObsoleteReferences();


    strongRefCache.put( key, value );
    SoftReference ref = (SoftReference) softRefCache.put(
        key,
        new KeyedSoftReference( key, value, referenceQueue )
    );


    return ( ref != null ) ? ref.get() : null;
  }

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            return value;
        }


        public void put(String key, Object value) {
            if (value != null) {
                CACHE.put(prefix + key, new SoftReference(value));
            }
            else
                CACHE.remove(prefix + key); 
            expiryTime = -1;
        }

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        }


        public void put(String key, Object value, long timeToLive) {
            if (value != null) {
                expiryTime = System.currentTimeMillis() + timeToLive*1000;
                CACHE.put(prefix + key, new SoftReference(value));
            }
            else {
                CACHE.remove(prefix + key);
                expiryTime = -1;
            }

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                // we're using the parser only as an XNI-to-SAX converter,
                // so that we can use the SAX-based serializer
                SAXParser parser = (SAXParser) fParser.get();
                if (newConfig || parser == null) {
                    parser = new SAXParser(config);
                    fParser = new SoftReference(parser);
                }
                else {
                    parser.reset();
                }
                config.setDocumentHandler(fSchemaValidator);

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        config.setProperty(VALIDATION_MANAGER, fComponentManager.getProperty(VALIDATION_MANAGER));
        config.setProperty(SECURITY_MANAGER, fComponentManager.getProperty(SECURITY_MANAGER));
        config.setDocumentHandler(fSchemaValidator);
        config.setDTDHandler(null);
        config.setDTDContentModelHandler(null);
        fConfiguration = new SoftReference(config);
        return config;
    }

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            // create new validator - we should not attempt
            // to restrict the number of validation handlers being
            // requested
            while (freeSchemaValidatorIndex >= 0) {
                // return first available validator
                SoftReference ref = schemaValidators[freeSchemaValidatorIndex];
                RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
                if (holder != null && holder.handler != null) {
                    RevalidationHandler val = holder.handler;
                    holder.handler = null;
                    --freeSchemaValidatorIndex;
                    return val;
                }
                schemaValidators[freeSchemaValidatorIndex--] = null;
            }
            //MF
            return (RevalidationHandler) (ObjectFactory
                    .newInstance(
                        "mf.org.apache.xerces.impl.xs.XMLSchemaValidator",
                        ObjectFactory.findClassLoader(),
                        true));
        }
        else if(schemaType == XMLGrammarDescription.XML_DTD) {
            // return an instance of XML11DTDValidator
            if ("1.1".equals(xmlVersion)) {
                while (freeXML11DTDValidatorIndex >= 0) {
                    // return first available validator
                    SoftReference ref = xml11DTDValidators[freeXML11DTDValidatorIndex];
                    RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
                    if (holder != null && holder.handler != null) {
                        RevalidationHandler val = holder.handler;
                        holder.handler = null;
                        --freeXML11DTDValidatorIndex;
                        return val;
                    }
                    xml11DTDValidators[freeXML11DTDValidatorIndex--] = null;
                }
                //MF
                return (RevalidationHandler) (ObjectFactory
                        .newInstance(
                                "mf.org.apache.xerces.impl.dtd.XML11DTDValidator",
                                ObjectFactory.findClassLoader(),
                                true));
            }
            // return an instance of XMLDTDValidator
            else {
                while (freeXML10DTDValidatorIndex >= 0) {
                    // return first available validator
                    SoftReference ref = xml10DTDValidators[freeXML10DTDValidatorIndex];
                    RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
                    if (holder != null && holder.handler != null) {
                        RevalidationHandler val = holder.handler;
                        holder.handler = null;
                        --freeXML10DTDValidatorIndex;
                        return val;

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      if (schemaType == XMLGrammarDescription.XML_SCHEMA) {
          ++freeSchemaValidatorIndex;
          if (schemaValidators.length == freeSchemaValidatorIndex) {
              // resize size of the validators
              schemaValidatorsCurrentSize += SIZE;
              SoftReference newarray[] =  new SoftReference[schemaValidatorsCurrentSize];
              System.arraycopy(schemaValidators, 0, newarray, 0, schemaValidators.length);
              schemaValidators = newarray;
          }
          SoftReference ref = schemaValidators[freeSchemaValidatorIndex];
          if (ref != null) {
              RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
              if (holder != null) {
                  holder.handler = validator;
                  return;
              }
          }
          schemaValidators[freeSchemaValidatorIndex] = new SoftReference(new RevalidationHandlerHolder(validator));
      }
      else if (schemaType == XMLGrammarDescription.XML_DTD) {
          // release an instance of XML11DTDValidator
          if ("1.1".equals(xmlVersion)) {
              ++freeXML11DTDValidatorIndex;
              if (xml11DTDValidators.length == freeXML11DTDValidatorIndex) {
                  // resize size of the validators
                  xml11DTDValidatorsCurrentSize += SIZE;
                  SoftReference [] newarray = new SoftReference[xml11DTDValidatorsCurrentSize];
                  System.arraycopy(xml11DTDValidators, 0, newarray, 0, xml11DTDValidators.length);
                  xml11DTDValidators = newarray;
              }
              SoftReference ref = xml11DTDValidators[freeXML11DTDValidatorIndex];
              if (ref != null) {
                  RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
                  if (holder != null) {
                      holder.handler = validator;
                      return;
                  }
              }
              xml11DTDValidators[freeXML11DTDValidatorIndex] = new SoftReference(new RevalidationHandlerHolder(validator));
          }
          // release an instance of XMLDTDValidator
          else {
              ++freeXML10DTDValidatorIndex;
              if (xml10DTDValidators.length == freeXML10DTDValidatorIndex) {
                  // resize size of the validators
                  xml10DTDValidatorsCurrentSize += SIZE;
                  SoftReference [] newarray = new SoftReference[xml10DTDValidatorsCurrentSize];
                  System.arraycopy(xml10DTDValidators, 0, newarray, 0, xml10DTDValidators.length);
                  xml10DTDValidators = newarray;
              }
              SoftReference ref = xml10DTDValidators[freeXML10DTDValidatorIndex];
              if (ref != null) {
                  RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
                  if (holder != null) {
                      holder.handler = validator;
                      return;
                  }
              }
              xml10DTDValidators[freeXML10DTDValidatorIndex] = new SoftReference(new RevalidationHandlerHolder(validator));
          }
      }
  }

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