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.Date;
   8 import java.util.Iterator;
   9 import java.util.LinkedList;
  10
  11 /**
  12  * A utility class that does various checks on search and indexing parameters.
  13  *
  14  */
  15 @AppEngineInternal
  16 public final class Util {
  17
  18   private static final long MILLISECONDS_IN_DAY = 1000L * 60 * 60 * 24;
  19
  20   private Util() {
  21   }
  22
  23   /**
  24    * A helper method for testing two objects are equal.
  25    *
  26    * @return whether the two objects a and b are equal
  27    */
  28   public static boolean equalObjects(Object a, Object b) {
  29     return a == b || (a != null && a.equals(b));
  30   }
  31
  32   /**
  33    * A helper method for overriding null values with a default value.
  34    *
  35    * @param value the value of some field
  36    * @param defaultValue the default value for the field
  37    * @return value if it is not null, otherwise the defaultValue
  38    */
  39   public static <T> T defaultIfNull(T value, T defaultValue) {
  40     return value == null ? defaultValue : value;
  41   }
  42
  43   /**
  44    * Returns a string representation of the iterable objects. This is
  45    * used in debugging. The limit parameter is used to control how many
  46    * elements of the iterable are used to build the final string. Use
  47    * 0 or negative values, to include all.
  48    *
  49    * @param objects an iterable of objects to be turned into a string
  50    * @param limit the maximum number of objects from iterable to be used
  51    * to build a string
  52    */
  53   public static <T> String iterableToString(Iterable<T> objects, int limit) {
  54     StringBuilder builder = new StringBuilder()
  55         .append("[");
  56     String sep = "";
  57     int head = (limit <= 0) ? Integer.MAX_VALUE : (limit + 1) / 2;
  58     int tail = (limit <= 0) ? 0 : limit - head;
  59     Iterator<T> iter = objects.iterator();
  60     while (iter.hasNext() && --head >= 0) {
  61       builder.append(sep).append(iter.next().toString());
  62       sep = ", ";
  63     }
  64     LinkedList<T> tailMembers = new LinkedList<T>();
  65     int seen = 0;
  66     while (iter.hasNext()) {
  67       tailMembers.add(iter.next());
  68       if (++seen > tail) {
  69         tailMembers.removeFirst();
  70       }
  71     }
  72     if (seen > tail) {
  73       builder.append(", ...");
  74     }
  75     for (T o : tailMembers) {
  76       builder.append(sep).append(o.toString());
  77       sep = ", ";
  78     }
  79     return builder.append("]").toString();
  80   }
  81
  82   /**
  83    * Returns a string which can be used to append an iterable field to a debug
  84    * string.
  85    */
  86   public static <T> String iterableFieldToString(String fieldName, Iterable<T> objects) {
  87     if (!objects.iterator().hasNext()) {
  88       return "";
  89     }
  90     return String.format(", %s=%s", fieldName, Util.iterableToString(objects, 0));
  91   }
  92
  93   /**
  94    * Returns a string that allows a field value pair to be added to a debug
  95    * string.
  96    */
  97   public static String fieldToString(String name, Object value) {
  98     return fieldToString(name, value, false);
  99   }
 100
 101   /**
 102    * Returns a string that allows a field value pair to be added to a debug
 103    * string.
 104    */
 105   public static String fieldToString(String name, Object value, boolean firstParameter) {
 106     if (value == null) {
 107       return "";
 108     }
 109     if (firstParameter) {
 110       return String.format("%s=%s",  name, value);
 111     }
 112     return String.format(", %s=%s",  name, value);
 113   }
 114
 115   /**
 116    * Converts a given date to a numeric value, ignoring any time component.
 117    *
 118    * @param date the date to convert to an int
 119    * @return a number representing the given date
 120    * @deprecated as of 1.7.2
 121    */
 122   @Deprecated
 123   public static int getIntForDate(Date date) {
 124     return (int) (date.getTime() / MILLISECONDS_IN_DAY);
 125   }
 126 }