Guava简介

Google Guava很优秀，大有取代Apache Commons之势。闲话少叙，直接上Guava的终极目标，用原汁原味的英文来说就是“Our goal is for you to write less code and for the code you do write to be simpler, cleaner, and more readable”，Guava中主要包括Basic Utilities，Collections，Caches，Functional Idioms，Concurrency，Strings，Primitives Support，Ranges，I/O等等，API参考文档点我，Guava在Github上仓库地址点我

Guava使用示例

Preconditions

可以用在方法的开始或者是构造函数的开始，对于不合法的校验可以快速报错

  1. package cn.codepub.guava.demo;
  3. import static com.google.common.base.Preconditions.checkArgument;
  4. import static com.google.common.base.Preconditions.checkNotNull;
  6. /**
  7.  * <p>
  8.  * Created with IntelliJ IDEA. 2015/11/28 20:12
  9.  * </p>
  10.  * <p>
  11.  * ClassName:PreconditionsDemo
  12.  * </p>
  13.  * <p>
  14.  * Description:TODO
  15.  * </P>
  16.  *
  17.  * @author Wang Xu
  18.  * @version V1.0.0
  19.  * @since V1.0.0
  20.  */
  21. public class PreconditionsDemo {
  22.     public static void main(String[] args) {
  23.         new Car(null);//Exception in thread "main" java.lang.NullPointerException
  24.         //Exception in thread "main" java.lang.IllegalArgumentException: speed (0.0) must be positive
  25.         new Car("Audi").drive(0);
  26.     }
  28. }
  29. class Car {
  30.     private String name;
  32.     public Car(String name) {
  33.         this.name = checkNotNull(name);//NPE Null Pointer Exception
  34.     }
  35.     public void drive(double speed) {
  36.         checkArgument(speed > 0.0, "speed (%s) must be positive", speed);
  37.     }
  38. }
MoreObjects.toStringHelper()

让你可以更优雅的覆写Object.toString()方法

  1. package cn.codepub.guava.demo;
  3. import com.google.common.base.MoreObjects;
  5. /**
  6.  * <p>
  7.  * Created with IntelliJ IDEA. 2015/11/28 20:26
  8.  * </p>
  9.  * <p>
  10.  * ClassName:MoreObjectsDemo
  11.  * </p>
  12.  * <p>
  13.  * Description:TODO
  14.  * </P>
  15.  *
  16.  * @author Wang Xu
  17.  * @version V1.0.0
  18.  * @since V1.0.0
  19.  */
  20. public class MoreObjectsDemo {
  21.     private String name;
  22.     private String userId;
  23.     private String petName;
  24.     private String sex;
  26.     @Override
  27.     public String toString() {
  28.         //prints:MoreObjectsDemo{name=testName, userId=NO1, petName=PIG}
  29.         return MoreObjects.toStringHelper(this).add("name", "testName").add("userId", "NO1").add("petName", "PIG").omitNullValues().toString();
  30.         //prints:MoreObjectsDemo{name=testName, userId=NO1, petName=PIG}
  31.         //return MoreObjects.toStringHelper(this).add("name", "testName").add("userId", "NO1").add("petName", "PIG").toString();
  32.     }
  33.     public static void main(String[] args) {
  34.         System.out.println(new MoreObjectsDemo());
  35.     }
  36. }
用Stopwatch代替System.nanoTime()

简单点说就是Stopwatch使用纳秒计时，使用该类度量时间比使用System.nanoTime()好，好处在哪呢？基于性能和测试来说，它可以作为另一种替代时间源；根据System.nanoTime()的说明，返回的值没有绝对意义，只能解释为相对于另一个返回的时间戳。Stopwatch是一个更有效的抽象,因为它只公开这些相对的值,而不是绝对值。可以通过其提供的start和stop方法得到。

  1. package cn.codepub.guava.demo;
  3. import com.google.common.base.Stopwatch;
  5. import java.util.concurrent.TimeUnit;
  7. /**
  8.  * <p>
  9.  * Created with IntelliJ IDEA. 2015/11/28 20:53
  10.  * </p>
  11.  * <p>
  12.  * ClassName:StopWatchDemo
  13.  * </p>
  14.  * <p>
  15.  * Description:TODO
  16.  * </P>
  17.  *
  18.  * @author Wang Xu
  19.  * @version V1.0.0
  20.  * @since V1.0.0
  21.  */
  22. public class StopWatchDemo {
  23.     public static void main(String[] args) {
  24.         //The Construct Stopwatch is default access permissions
  26.         Stopwatch stopwatch = Stopwatch.createUnstarted();
  27.         //start
  28.         stopwatch.start();
  29.         System.out.println("You can do something!");
  30.         try {
  31.             Thread.sleep(1000);
  32.         } catch (InterruptedException e) {
  33.             e.printStackTrace();
  34.         }
  35.         stopwatch.stop();
  36.         long nanos = stopwatch.elapsed(TimeUnit.NANOSECONDS);
  37.         System.out.println(nanos);//1000076976
  38.     }
  39. }
CharMatcher
  1. package cn.codepub.guava.demo;
  3. import com.google.common.base.CharMatcher;
  5. /**
  6.  * <p>
  7.  * Created with IntelliJ IDEA. 2015/11/28 21:31
  8.  * </p>
  9.  * <p>
  10.  * ClassName:CharMatcherDemo
  11.  * </p>
  12.  * <p>
  13.  * Description:TODO
  14.  * </P>
  15.  *
  16.  * @author Wang Xu
  17.  * @version V1.0.0
  18.  * @since V1.0.0
  19.  */
  20. public class CharMatcherDemo {
  21.     private static final CharMatcher ID_MATCHER = CharMatcher.DIGIT.or(CharMatcher.is('-'));
  23.     public static void main(String[] args) {
  24.         String userID = "123454-333";
  25.         String s = ID_MATCHER.retainFrom(userID);
  26.         System.out.println(s);//123454-333
  27.         s = ID_MATCHER.retainFrom("1    test    11-222");
  28.         System.out.println(s);//111-222
  29.     }
  30. }
String Joining
  1. package cn.codepub.guava.demo;
  3. import com.google.common.base.Joiner;
  5. /**
  6.  * <p>
  7.  * Created with IntelliJ IDEA. 2015/11/28 21:43
  8.  * </p>
  9.  * <p>
  10.  * ClassName:StringJoiningDemo
  11.  * </p>
  12.  * <p>
  13.  * Description:TODO
  14.  * </P>
  15.  *
  16.  * @author Wang Xu
  17.  * @version V1.0.0
  18.  * @since V1.0.0
  19.  */
  20. public class StringJoiningDemo {
  21.     private static final Joiner JOINER = Joiner.on(",").skipNulls();
  22.     //set replace string
  23.     private static final Joiner JOINER_USE_FOR_NULL = Joiner.on(",").useForNull("replace");
  25.     public static void main(String[] args) {
  26.         String join = JOINER.join("Kurt", "Kevin", null, "Chris");
  27.         System.out.println(join);//Kurt, Kevin, Chris
  28.         join = JOINER_USE_FOR_NULL.join("Kurt", "Kevin", null, "Chris");
  29.         System.out.println(join);
  30.     }
  31. }
String Splitting

使用指定的分隔符对字符串进行拆分，默认对空白符不做任何处理，并且不会静默的丢弃末尾分隔符，如果需要处理的话要显式调用trimResults()，omitEmptyStrings()

  1. package cn.codepub.guava.demo;
  3. import com.google.common.base.Splitter;
  5. /**
  6.  * <p>
  7.  * Created with IntelliJ IDEA. 2015/11/28 21:57
  8.  * </p>
  9.  * <p>
  10.  * ClassName:SplitterDemo
  11.  * </p>
  12.  * <p>
  13.  * Description:TODO
  14.  * </P>
  15.  *
  16.  * @author Wang Xu
  17.  * @version V1.0.0
  18.  * @since V1.0.0
  19.  */
  20. public class SplitterDemo {
  21.     public static void main(String[] args) {
  22.         Iterable<String> split = Splitter.on(',').trimResults().omitEmptyStrings()
  23.         .split("foo, ,bar,quux,blue,");
  24.         for (String s : split) {
  25.             System.out.print(s + "---");//foo---bar---quux---blue---
  26.         }
  27.         System.out.println();
  28.         String[] split1 = "foo, ,bar,quux,blue,".split(",");
  29.         for (String s : split1) {
  30.             System.out.print(s + "---");//foo--- ---bar---quux---blue---
  31.         }
  32.     }
  34. }
Optional
  1. package cn.codepub.guava.demo;
  3. import java.util.Optional;
  5. /**
  6.  * <p>
  7.  * Created with IntelliJ IDEA. 2015/11/28 22:24
  8.  * </p>
  9.  * <p>
  10.  * ClassName:OptionalDemo
  11.  * </p>
  12.  * <p>
  13.  * Description:TODO
  14.  * </P>
  15.  *
  16.  * @author Wang Xu
  17.  * @version V1.0.0
  18.  * @since V1.0.0
  19.  */
  20. public class OptionalDemo {
  21.     public static void main(String[] args) {
  22.         //Creating an Optional<T>
  23.         //Optional.of(notNull);
  24.         //Optional.empty();
  25.         //Optional.ofNullable(maybeNull);
  26.         String test = "test";
  27.         // if test == null will throws NPE
  28.         Optional<String> s = Optional.of(test);
  29.         System.out.println(s.get());//test
  31.         Optional<Object> empty = Optional.empty();
  32.         System.out.println(empty);//Optional.empty
  34.         Optional<Object> o = Optional.ofNullable(null);
  35.         System.out.println(o);//Optional.empty
  36.     }
  38. }
Hashing
  1. package cn.codepub.guava.demo;
  3. import com.google.common.base.Charsets;
  4. import com.google.common.hash.HashCode;
  5. import com.google.common.hash.Hashing;
  7. /**
  8.  * <p>
  9.  * Created with IntelliJ IDEA. 2015/11/29 16:24
  10.  * </p>
  11.  * <p>
  12.  * ClassName:HashingDemo
  13.  * </p>
  14.  * <p>
  15.  * Description:TODO
  16.  * </P>
  17.  *
  18.  * @author Wang Xu
  19.  * @version V1.0.0
  20.  * @since V1.0.0
  21.  */
  22. public class HashingDemo {
  23.     public static void main(String[] args) {
  24.         byte sex = 1;
  25.         Person person = new Person(100, "eric", "wang", 1L, sex);
  26.         System.out.println(person.hashCode());//1935260882
  27.     }
  28. }
  29. class Person {
  30.     private int age;
  31.     private String firstName;
  32.     private String lastName;
  33.     private long id;
  34.     private byte sex;
  36.     public Person(int age, String firstName, String lastName, long id, byte sex) {
  37.         this.age = age;
  38.         this.firstName = firstName;
  39.         this.lastName = lastName;
  40.         this.id = id;
  41.         this.sex = sex;
  42.     }
  44.     public int getAge() {
  45.         return this.age;
  46.     }
  48.     public String getFirstName() {
  49.         return this.firstName;
  50.     }
  52.     public String getLastName() {
  53.         return this.lastName;
  54.     }
  56.     public long getId() {
  57.         return this.id;
  58.     }
  60.     public byte getSex() {
  61.         return this.sex;
  62.     }
  64.     @Override
  65.     public int hashCode() {
  66.         HashCode hashCode = Hashing.murmur3_128().newHasher().putInt(this.getAge()).putLong(this.getId())
  67.         .putString(this.getFirstName(), Charsets.UTF_8).putString(this.getLastName(), Charsets.UTF_8)
  68.         .putByte(this.getSex()).hash();
  69.         return hashCode.hashCode();
  70.     }
  71. }
Caching
  1. package cn.codepub.guava.demo;
  3. import com.google.common.cache.*;
  4. import com.sun.corba.se.impl.orbutil.graph.Graph;
  6. import java.security.Key;
  7. import java.util.concurrent.TimeUnit;
  9. /**
  10.  * <p>
  11.  * Created with IntelliJ IDEA. 2015/11/29 16:54
  12.  * </p>
  13.  * <p>
  14.  * ClassName:CachingDemo
  15.  * </p>
  16.  * <p>
  17.  * Description:TODO
  18.  * </P>
  19.  *
  20.  * @author Wang Xu
  21.  * @version V1.0.0
  22.  * @since V1.0.0
  23.  */
  24. public class CachingDemo {
  25.     LoadingCache<Key, Graph> cache = CacheBuilder.newBuilder().maximumSize(10000)
  26.     .expireAfterWrite(10, TimeUnit.MINUTES).removalListener(new RemovalListener<Object, Object>() {
  27.         @Override
  28.         public void onRemoval(RemovalNotification<Object, Object> removalNotification) {
  29.             //implements your listener
  30.         }
  31.     }).build(new CacheLoader<Key, Graph>() {
  32.         @Override
  33.         public Graph load(Key key) throws Exception {
  34.             return null;
  35.         }
  36.     });
  37. }
链式调用

Guava中提供了大量方法，让我们可以使用链式调用的方式从而减少代码量。简单来说方法链一般适合对一个对象进行连续操作（集中在一句代码）。一定程度上可以减少代码量，缺点是它占用了函数的返回值。如果不需要使用到函数返回值的话，建议大家在封装自己的代码库的时候可以使用这种方式，提供一个简单的demo如下：

  1. package cn.codepub.guava.demo;
  3. /**
  4.  * <p>
  5.  * Created with IntelliJ IDEA. 2015/11/29 16:00
  6.  * </p>
  7.  * <p>
  8.  * ClassName:ChainEncapsulationDemo
  9.  * </p>
  10.  * <p>
  11.  * Description:TODO
  12.  * </P>
  13.  *
  14.  * @author Wang Xu
  15.  * @version V1.0.0
  16.  * @since V1.0.0
  17.  */
  18. public class ChainEncapsulationDemo {
  19.     private String message = "";
  21.     public String getMessage() {
  22.         return message;
  23.     }
  25.     public void setMessage(String message) {
  26.         this.message = message;
  27.     }
  29.     public static void main(String[] args) {
  30.         ChainEncapsulationDemo chainEncapsulationDemo = new ChainEncapsulationDemo();
  31.         chainEncapsulationDemo = chainEncapsulationDemo.method1().method2().method3();
  32.         System.out.println(chainEncapsulationDemo.getMessage());
  34.     }
  36.     public ChainEncapsulationDemo method1() {
  37.         this.setMessage(this.getMessage() + "add method1 ...\n");
  38.         return this;
  39.     }
  42.     public ChainEncapsulationDemo method2() {
  43.         this.setMessage(this.getMessage() + "add method2 ...\n");
  44.         return this;
  45.     }
  47.     public ChainEncapsulationDemo method3() {
  48.         this.setMessage(this.getMessage() + "add method3 ...");
  49.         return this;
  50.     }
  51. }
Apache VS. Guava

关于使用Apache Commons还是Guava的讨论看这里