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 java.util.Iterator;
   6 import java.util.LinkedList;
   7
   8 /**
   9  * A utility class that does various checks on search and indexing parameters.
  10  */
  11 final class Util {
  12   /**
  13    * A helper method for testing two objects are equal.
  14    *
  15    * @return whether the two objects a and b are equal
  16    */
  17   static boolean equalObjects(Object a, Object b) {
  18     return a == b || (a != null && a.equals(b));
  19   }
  20
  21   /**
  22    * A helper method for overriding null values with a default value.
  23    *
  24    * @param value the value of some field
  25    * @param defaultValue the default value for the field
  26    * @return value if it is not null, otherwise the defaultValue
  27    */
  28   static <T> T defaultIfNull(T value, T defaultValue) {
  29     return value == null ? defaultValue : value;
  30   }
  31
  32   /**
  33    * Returns a string representation of the iterable objects. This is
  34    * used in debugging. The limit parameter is used to control how many
  35    * elements of the iterable are used to build the final string. Use
  36    * 0 or negative values, to include all.
  37    *
  38    * @param objects an iterable of objects to be turned into a string
  39    * @param limit the maximum number of objects from iterable to be used
  40    * to build a string
  41    */
  42   static <T> String iterableToString(Iterable<T> objects, int limit) {
  43     StringBuilder builder = new StringBuilder()
  44         .append("[");
  45     String sep = "";
  46     int head = (limit <= 0) ? Integer.MAX_VALUE : (limit + 1) / 2;
  47     int tail = (limit <= 0) ? 0 : limit - head;
  48     Iterator<T> iter = objects.iterator();
  49     while (iter.hasNext() && --head >= 0) {
  50       builder.append(sep).append(iter.next());
  51       sep = ", ";
  52     }
  53     LinkedList<T> tailMembers = new LinkedList<T>();
  54     int seen = 0;
  55     while (iter.hasNext()) {
  56       tailMembers.add(iter.next());
  57       if (++seen > tail) {
  58         tailMembers.removeFirst();
  59       }
  60     }
  61     if (seen > tail) {
  62       builder.append(", ...");
  63     }
  64     for (T o : tailMembers) {
  65       builder.append(sep).append(o);
  66       sep = ", ";
  67     }
  68     return builder.append("]").toString();
  69   }
  70
  71   /**
  72    * Helper for constructing {@link String} representations of Search API objects.
  73    */
  74   static class ToStringHelper {
  75     private final StringBuilder sb;
  76     private boolean first = true;
  77     private boolean done = false;
  78
  79     ToStringHelper(String objectName) {
  80       sb = new StringBuilder(objectName + "(");
  81     }
  82
  83     ToStringHelper addField(String fieldName, Object value) {
  84       if (done) {
  85         throw new IllegalStateException();
  86       }
  87       if (value != null) {
  88         if (first) {
  89           first = false;
  90         } else {
  91           sb.append(", ");
  92         }
  93         sb.append(fieldName).append("=").append(value);
  94       }
  95       return this;
  96     }
  97
  98     ToStringHelper addIterableField(String fieldName, Iterable<?> objects, int max) {
  99       if (done) {
 100         throw new IllegalStateException();
 101       }
 102       Iterator<?> iterator = objects.iterator();
 103       if (iterator.hasNext()) {
 104         if (first) {
 105           first = false;
 106         } else {
 107           sb.append(", ");
 108         }
 109         sb.append(fieldName).append("=").append(Util.iterableToString(objects, max));
 110       }
 111       return this;
 112     }
 113
 114     ToStringHelper addIterableField(String fieldName, Iterable<?> objects) {
 115       return addIterableField(fieldName, objects, 0);
 116     }
 117
 118     String finish() {
 119       done = true;
 120       sb.append(")");
 121       return sb.toString();
 122     }
 123
 124     @Override
 125     public String toString() {
 126       return done ? sb.toString() : sb + ")";
 127     }
 128   }
 129
 130   private Util() {}
 131 }