Guava(石榴)使用研究-Google开源Collection类库

1)Guava?简介

Guava 中文是石榴的意思，该项目是 Google 的一个开源项目，包含许多 Google 核心的 Java 常用库。

目前主要包含：

• com.google.common.annotations
• com.google.common.base
• com.google.common.collect
• com.google.common.io
• com.google.common.net
• com.google.common.primitives
• com.google.common.util.concurrent

  在线API doc：http://www.osctools.net/apidocs/apidoc?api=guava

  2)代码实现

  package test;

  ?

  import java.text.DecimalFormat;

  import java.util.Arrays;

  import java.util.Collection;

  import java.util.Collections;

  import java.util.Comparator;

  import java.util.HashMap;

  import java.util.HashSet;

  import java.util.List;

  import java.util.Map;

  import java.util.Set;

  import java.util.concurrent.ConcurrentMap;

  import java.util.concurrent.TimeUnit;

  ?

  import com.google.common.base.Function;

  import com.google.common.base.Predicate;

  import com.google.common.collect.Collections2;

  import com.google.common.collect.HashMultimap;

  import com.google.common.collect.HashMultiset;

  import com.google.common.collect.ImmutableSet;

  import com.google.common.collect.Lists;

  import com.google.common.collect.MapMaker;

  import com.google.common.collect.Ordering;

  import com.google.common.collect.ImmutableSet.Builder;

  ?

  /**

  ?* @author gaozzsoft

  ?*

  ?*/

  public class MyGuavaTest {

  ?

  /**

  * @param args

  */

  public static void main(String[] args) {

  // TODO Auto-generated method stub

  List list = Lists.newArrayList();

  ?

  //1 Immutable Collections: 真正的不可修改的集合

  Set<String> set = new HashSet<String>(Arrays.asList(new String[]{"RED", "GREEN"}));?

  Set<String> unmodifiableSet = Collections.unmodifiableSet(set);?

  ?

  ImmutableSet<String> immutableSet = ImmutableSet.of("RED", "GREEN");?

  ?

  ImmutableSet<String> immutableSet2 = ImmutableSet.copyOf(set);?

  ?

  Builder<String> ?builder = ImmutableSet.builder();?

  ImmutableSet<String> immutableSet3 = builder.add("RED").addAll(set).build();?

  ?

  // Multiset: 把重复的元素放入集合

  List<String> wordList =Arrays.asList(new String[]{"RED", "GREEN"});

  Map<String, Integer> map = new HashMap<String, Integer>();?

  for(String word : wordList){?

  ? ?Integer count = map.get(word);?

  ? ?map.put(word, (count == null) ? 1 : count + 1);?

  }?

  //count word “RED”

  Integer count = map.get("RED");?

  ?

  // Quit good method

  HashMultiset<String> multiSet = HashMultiset.create();?

  multiSet.addAll(wordList);?

  //count word “RED”

  Integer count2 = multiSet.count("RED");?

  ?

  ?

  ?

  //2 Multimap: 在 Map 的 value 里面放多个元素

  //Key is candidate name, its value is his voters?

  HashMap<String, HashSet<String>> hMap = new HashMap<String, HashSet<String>>();?

  List<Ticket> tickets = Lists.newArrayList();

  Ticket ticket1 = new Ticket("xijinping","gaozz");

  Ticket ticket2 = new Ticket("xijinping","saiwg");

  tickets.add(ticket1);

  tickets.add(ticket2);

  ?

  for(Ticket ticket: tickets){?

  ? ?HashSet<String> set2 = hMap.get(ticket.getCandidate());?

  ? ?if(set2 == null){?

  ? ?set2 = new HashSet<String>();?

  ? ? ? ?hMap.put(ticket.getCandidate(), set2);?

  ? ?}?

  ? ?set2.add(ticket.getVoter());?

  }

  ?

  HashMultimap<String, String> map2 = HashMultimap.create();?

  for(Ticket ticket: tickets){?

  ? ?map2.put(ticket.getCandidate(), ticket.getVoter());?

  }?

  ?

  //3 BiMap: 双向 Map

  ?

  // for(Map.Entry<User, Address> entry : map.entreSet()){?

  // ? ?if(entry.getValue().equals(anAddess)){?

  // ? ? ? ?return entry.getKey();?

  // ? ?}?

  // }?

  // ? ? return null;?

  ?

  // return biMap.inverse().get(anAddess);?

  // biMap == biMap.inverse().inverse();

  ?

  //4 MapMaker: 超级强大的 Map 构造工具

  ?

  //ConcurrentHashMap with concurrency level 8?

  ConcurrentMap<String, Object> map1 = new MapMaker()?

  ? ?.concurrencyLevel(8)?

  ? ? .makeMap();?

  ?

  //ConcurrentMap with soft reference key and weak reference value?

  ConcurrentMap<String, Object> map3 = new MapMaker()?

  ? ?.softKeys()?

  ? ?.weakValues()?

  ? ?.makeMap();?

  ?

  //Automatically removed entries from map after 30 seconds since they are created?

  ConcurrentMap<String, Object> map4 = new MapMaker()

  ? ?.expireAfterWrite(30, TimeUnit.SECONDS)?

  ? ?.makeMap();

  ?

  ?

  //Map size grows close to the 100, the map will evict?

  //entries that are less likely to be used again?

  ConcurrentMap<String, Object> map5 = new MapMaker()

  ? ?.maximumSize(100)?

  ? ?.makeMap();?

  ?

  //Create an Object to the map, when get() is missing in map?

  ConcurrentMap<String, Object> map6 = new MapMaker()?

  ? ?.makeComputingMap(?

  ? ? ?new Function<String, Object>() {?

  ? ? ? ?public Object apply(String key) {?

  // ? ? ? ? ?return createObject(key);?

  ? ? ? ?return null;

  ? ?}});?

  ?

  ?

  //Put all features together! ?强大之处

  ConcurrentMap<String, Object> mapAll = new MapMaker()?

  ? ?.concurrencyLevel(8)?

  ? ?.softKeys()?

  ? ?.weakValues()?

  ? ?.expireAfterWrite(30, TimeUnit.SECONDS)?

  ? ?.maximumSize(100)?

  ? ?.makeComputingMap(?

  ? ? ?new Function<String, Object>() {?

  ? ? ? ?public Object apply(String key) {?

  // ? ? ? ? ?return createObject(key);?

  ? ? ? ? ?return null;

  ? ? }});?

  ?

  //5 元素排序

  //假设有个待排序的 List<Foo>，而 Foo 里面有两个排序关键字 int a, int b 和 int c

  // Collections.sort(list, new Comparator<Foo>(){ ? ?

  // ? ?@Override ? ?

  // ? ?public int compare(Foo f1, Foo f2) { ? ?

  // ? ? ? ?int resultA = f1.a f2.a;?

  // ? ? ? ?int resultB = f1.b f2.b;?

  // ? ? ? ?return ?resultA == 0 ? (resultB == 0 ? f1.c f2.c : resultB) : resultA;?

  //}});

  ?

  // Collections.sort(list, new Comparator<Foo>(){ ? ?

  // ? ?@Override?

  // ? ?return ComparisonChain.start() ?

  // ? ? ? ? .compare(f1.a, f2.a) ?

  // ? ? ? ? .compare(f1.b, f2.b)?

  // ? ? ? ? .compare(f1.c, f2.c).result();?

  //}});

  ?

  // Foo 里面每个排序关键字都已经有了各自的 Comparator，那么利用 ComparisonChain 可以?

  // Collections.sort(list, new Comparator<Foo>(){ ? ?

  // ? ?@Override?

  // ? ?return ComparisonChain.start() ?

  // ? ? ? ? .compare(f1.a, f2.a, comparatorA) ?

  // ? ? ? ? .compare(f1.b, f2.b, comparatorB)?

  // ? ? ? ? .compare(f1.c, f2.c, comparatorC).result();?

  // ?}});

  ?

  //Ordring 类还提供了一个组合 Comparator 对象的方法

  // 而且 Ordring 本身实现了 Comparator 接口所以它能直接作为 Comparator 使用

  // Ordering<Foo> ordering = Ordering.compound(

  // ? ? Arrays.asList(comparatorA, comparatorB, comparatorC));?

  // Collections.sort(list, ordering);

  ?

  ?

  //6 过滤器&&转换器

  ?

  //过滤器

  Collection<Integer> ?filterCollection =?

  ? ? ? ?Collections2.filter(list, new Predicate<Integer>(){?

  // ? ?@Override?

  ? ?public boolean apply(Integer input) {?

  ? ? ? ?return input >= 10;?

  }});?

  ?

  //转换器

  Set<Integer> ?setTmp = null;

  Collection<String> ?formatCollection =?

  ? ? ?Collections2.transform(setTmp, new Function<Integer, String>(){?

  // ? ?@Override?

  ? ?public String apply(Integer input) {?

  ? ? ? ?return new DecimalFormat("#,###").format(input);?

  }} );?

  ?

  }

  }

  ?