java/src/main/com/google/appengine/api/search/Util.java

   1 // Copyright 2010 Google Inc. All Rights Reserved.
   2
   3 package com.google.appengine.api.search;
   4
   5 import com.google.apphosting.api.AppEngineInternal;
   6
   7 import java.util.Iterator;
   8 import java.util.LinkedList;
   9
  10 /**
  11  * A utility class that does various checks on search and indexing parameters.
  12  *
  13  */
  14 @AppEngineInternal
  15 public final class Util {
  16
  17   private static final long MILLISECONDS_IN_DAY = 1000L * 60 * 60 * 24;
  18
  19   private Util() {
  20   }
  21
  22   /**
  23    * A helper method for testing two objects are equal.
  24    *
  25    * @return whether the two objects a and b are equal
  26    */
  27   public static boolean equalObjects(Object a, Object b) {
  28     return a == b || (a != null && a.equals(b));
  29   }
  30
  31   /**
  32    * A helper method for overriding null values with a default value.
  33    *
  34    * @param value the value of some field
  35    * @param defaultValue the default value for the field
  36    * @return value if it is not null, otherwise the defaultValue
  37    */
  38   public static <T> T defaultIfNull(T value, T defaultValue) {
  39     return value == null ? defaultValue : value;
  40   }
  41
  42   /**
  43    * Returns a string representation of the iterable objects. This is
  44    * used in debugging. The limit parameter is used to control how many
  45    * elements of the iterable are used to build the final string. Use
  46    * 0 or negative values, to include all.
  47    *
  48    * @param objects an iterable of objects to be turned into a string
  49    * @param limit the maximum number of objects from iterable to be used
  50    * to build a string
  51    */
  52   public static <T> String iterableToString(Iterable<T> objects, int limit) {
  53     StringBuilder builder = new StringBuilder()
  54         .append("[");
  55     String sep = "";
  56     int head = (limit <= 0) ? Integer.MAX_VALUE : (limit + 1) / 2;
  57     int tail = (limit <= 0) ? 0 : limit - head;
  58     Iterator<T> iter = objects.iterator();
  59     while (iter.hasNext() && --head >= 0) {
  60       builder.append(sep).append(iter.next().toString());
  61       sep = ", ";
  62     }
  63     LinkedList<T> tailMembers = new LinkedList<T>();
  64     int seen = 0;
  65     while (iter.hasNext()) {
  66       tailMembers.add(iter.next());
  67       if (++seen > tail) {
  68         tailMembers.removeFirst();
  69       }
  70     }
  71     if (seen > tail) {
  72       builder.append(", ...");
  73     }
  74     for (T o : tailMembers) {
  75       builder.append(sep).append(o.toString());
  76       sep = ", ";
  77     }
  78     return builder.append("]").toString();
  79   }
  80
  81   /**
  82    * Returns a string which can be used to append an iterable field to a debug
  83    * string.
  84    */
  85   public static <T> String iterableFieldToString(String fieldName, Iterable<T> objects) {
  86     if (!objects.iterator().hasNext()) {
  87       return "";
  88     }
  89     return String.format(", %s=%s", fieldName, Util.iterableToString(objects, 0));
  90   }
  91
  92   /**
  93    * Returns a string that allows a field value pair to be added to a debug
  94    * string.
  95    */
  96   public static String fieldToString(String name, Object value) {
  97     return fieldToString(name, value, false);
  98   }
  99
 100   /**
 101    * Returns a string that allows a field value pair to be added to a debug
 102    * string.
 103    */
 104   public static String fieldToString(String name, Object value, boolean firstParameter) {
 105     if (value == null) {
 106       return "";
 107     }
 108     if (firstParameter) {
 109       return String.format("%s=%s",  name, value);
 110     }
 111     return String.format(", %s=%s",  name, value);
 112   }
 113 }