http://macrochen.iteye.com/blog/737058

参考:
http://codemunchies.com/2009/10/beautiful-code-with-google-collections-guava-and-static-imports-part-1/ (2,3,4)
http://blog.publicobject.com

更多用法参考http://ajoo.iteye.com/category/119082

以前这么用:

Map<String, Map<Long, List<String>>> map = new HashMap<String, Map<Long,List<String>>>();

现在这么用(JDK7将实现该功能):

Map<String, Map<Long, List<String>>> map = Maps.newHashMap();

针对不可变集合:
以前这么用:

List<String> list = new ArrayList<String>();
list.add("a");
list.add("b");
list.add("c");
list.add("d");

现在Guava这么用:

ImmutableList<String> of = ImmutableList.of("a", "b", "c", "d");
ImmutableMap<String,String> map = ImmutableMap.of("key1", "value1", "key2", "value2");

文本文件读取现在Guava这么用

File file = new File(getClass().getResource("/test.txt").getFile());
List<String> lines = null;
try {
lines = Files.readLines(file, Charsets.UTF_8);
} catch (IOException e) {
e.printStackTrace();
}

基本类型比较, 现在Guava这么用:

int compare = Ints.compare(a, b);

Guava中CharMatcher的用法:

assertEquals("89983", CharMatcher.DIGIT.retainFrom("some text 89983 and more"))
assertEquals("some text  and more", CharMatcher.DIGIT.removeFrom("some text 89983 and more"))

Guava中Joiner的用法:

int[] numbers = { 1, 2, 3, 4, 5 };
String numbersAsString = Joiner.on(";").join(Ints.asList(numbers));

另一种写法:

String numbersAsStringDirectly = Ints.join(";", numbers);

Guava中Splitter的用法:

Iterable split = Splitter.on(",").split(numbsAsString);

对于这样的字符串进行切分:

String testString = "foo , what,,,more,";
Iterable<String> split = Splitter.on(",").omitEmptyStrings().trimResults().split(testString);

Ints中一些用法:

int[] array = { 1, 2, 3, 4, 5 };
int a = 4;
boolean contains = Ints.contains(array, a);
int indexOf = Ints.indexOf(array, a);
int max = Ints.max(array);
int min = Ints.min(array);
int[] concat = Ints.concat(array, array2);

集合
set的交集, 并集, 差集的用法(http://publicobject.com/2008/08/coding-in-small-with-google-collections.html)

HashSet setA = newHashSet(1, 2, 3, 4, 5);
HashSet setB = newHashSet(4, 5, 6, 7, 8);
SetView union = Sets.union(setA, setB);
System.out.println("union:");
for (Integer integer : union)
System.out.println(integer);
SetView difference = Sets.difference(setA, setB);
System.out.println("difference:");
for (Integer integer : difference)
System.out.println(integer);
SetView intersection = Sets.intersection(setA, setB);
System.out.println("intersection:");
for (Integer integer : intersection)
System.out.println(integer);

针对Map的用法:

MapDifference differenceMap = Maps.difference(mapA, mapB);
differenceMap.areEqual();
Map entriesDiffering = differenceMap.entriesDiffering();
Map entriesOnlyOnLeft = differenceMap.entriesOnlyOnLeft();
Map entriesOnlyOnRight = differenceMap.entriesOnlyOnRight();
Map entriesInCommon = differenceMap.entriesInCommon();

验证与条件检查
原来的写法:

if (count <= 0) {
throw new IllegalArgumentException("must be positive: " + count);
}

Guava的写法(Jakarta Commons中有类似的方法):

Preconditions.checkArgument(count > 0, "must be positive: %s", count);

一个更酷的用法:

public PostExample(final String title, final Date date, final String author) {
this.title = checkNotNull(title);
this.date = checkNotNull(date);
this.author = checkNotNull(author);
}

如果一个key对应多个value的Map, 你会怎么处理? 如果还在使用Map<K, List<V>>的话, 你就out了
使用MultiMap吧:

Multimap<Person, BlogPost> multimap = ArrayListMultimap.create();

Multimap的另一个使用场景:
比如有一个文章数据的map:

List<Map<String, String>> listOfMaps = mapOf("type", "blog", "id", "292", "author", "john");

如果要按照type分组生成一个List

Multimap<String, Map<String, String>> partitionedMap = Multimaps.index(
listOfMaps,
new Function<Map<String, String>, String>() {
public String apply(final Map<String, String> from) {
return from.get("type");
}
}); 

针对集合中只有一个元素的情况:
Iterables.getOnlyElement();
这个主要是用来替换Set.iterator.next()或 List.get(0), 而且在测试中使用非常方便, 如果出现0个或者2+则直接抛出异常

比较的最大最小值:
Comparators.max
Comparators.min

equals和hashcode的用法:

  public boolean equals(Object o) {
if (o instanceof Order) {
Order that = (Order)o;
return Objects.equal(address, that.address)
&& Objects.equal(targetArrivalDate, that.targetArrivalDate)
&& Objects.equal(lineItems, that.lineItems);
} else {
return false;
}
}
public int hashCode() {
return Objects.hashCode(address, targetArrivalDate, lineItems);
}

ImmutableList.copyOf的用法:
以前这么用:

  public Directions(Address from, Address to, List<Step> steps) {
this.from = from;
this.to = to;
this.steps = Collections.unmodifiableList(new ArrayList<Step>(steps));
}

现在这么用:

  public Directions(Address from, Address to, List<Step> steps) {
this.from = from;
this.to = to;
this.steps = ImmutableList.of(steps);
}

Iterables.concat()的用法:
以前这么用:

  public boolean orderContains(Product product) {
List<LineItem> allLineItems = new ArrayList<LineItem>();
allLineItems.addAll(getPurchasedItems());
allLineItems.addAll(getFreeItems());
for (LineItem lineItem : allLineItems) {
if (lineItem.getProduct() == product) {
return true;
}
}
return false;
}

现在这么用:

  public boolean orderContains(Product product) {
for (LineItem lineItem : Iterables.concat(getPurchasedItems(), getFreeItems())) {
if (lineItem.getProduct() == product) {
return true;
}
}
return false;
}

Constraints.constrainedList: 给List操作注入约束逻辑, 比如添加不合法元素直接报错.
以前这么写:

  private final List<LineItem> purchases = new ArrayList<LineItem>();
/**
* Don't modify this! Instead, call {@link #addPurchase(LineItem)} to add
* new purchases to this order.
*/
public List<LineItem> getPurchases() {
return Collections.unmodifiableList(purchases);
}
public void addPurchase(LineItem purchase) {
Preconditions.checkState(catalog.isOffered(getAddress(), purchase.getProduct()));
Preconditions.checkState(purchase.getCharge().getUnits() > 0);
purchases.add(purchase);
}
现在这么写:
private final List<LineItem> purchases = Constraints.constrainedList(
new ArrayList<LineItem>(),
new Constraint<LineItem>() {
public void checkElement(LineItem element) {
Preconditions.checkState(catalog.isOffered(getAddress(), element.getProduct()));
Preconditions.checkState(element.getCharge().getUnits() > 0);
}
});
/**
* Returns the modifiable list of purchases in this order.
*/
public List<LineItem> getPurchases() {
return purchases;
}

不允许插入空值的Set(Constraints的用法):

        Set<String> set = Sets.newHashSet();
Set<String> constrainedSet = Constraints.constrainedSet(set, Constraints.notNull());
constrainedSet.add("A");
constrainedSet.add(null); // NullPointerException here

Multimap的用法(允许多值的map):
以前这么写:

  Map<Salesperson, List<Sale>> map = new Hashmap<SalesPerson, List<Sale>>();
public void makeSale(Salesperson salesPerson, Sale sale) {
List<Sale> sales = map.get(salesPerson);
if (sales == null) {
sales = new ArrayList<Sale>();
map.put(salesPerson, sales);
}
sales.add(sale);
}

现在这么写:

  Multimap<Salesperson, Sale> multimap
= new ArrayListMultimap<Salesperson,Sale>();
public void makeSale(Salesperson salesPerson, Sale sale) {
multimap.put(salesperson, sale);
}

以前这么写:

  public Sale getBiggestSale() {
Sale biggestSale = null;
for (List<Sale> sales : map.values()) {
Sale biggestSaleForSalesman
= Collections.max(sales, SALE_COST_COMPARATOR);
if (biggestSale == null
|| biggestSaleForSalesman.getCharge() > biggestSale().getCharge()) {
biggestSale = biggestSaleForSalesman;
}
}
return biggestSale;
}

现在这么写(需要将map转换成multimap):

  public Sale getBiggestSale() {
return Collections.max(multimap.values(), SALE_COST_COMPARATOR);
}

Joiner的用法:
以前这样写:

public class ShoppingList {
private List<Item> items = ...;
...
public String toString() {
StringBuilder stringBuilder = new StringBuilder();
for (Iterator<Item> s = items.iterator(); s.hasNext(); ) {
stringBuilder.append(s.next());
if (s.hasNext()) {
stringBuilder.append(" and ");
}
}
return stringBuilder.toString();
}
}

现在这样写:

public class ShoppingList {
private List<Item> items = ...;
...
public String toString() {
return Join.join(" and ", items);
}
}

Comparators.fromFunction的用法:
以前这样写:

 public Comparator<Product> createRetailPriceComparator(
final CurrencyConverter currencyConverter) {
return new Comparator<Product>() {
public int compare(Product a, Product b) {
return getRetailPriceInUsd(a).compareTo(getRetailPriceInUsd(b));
}
public Money getRetailPriceInUsd(Product product) {
Money retailPrice = product.getRetailPrice();
return retailPrice.getCurrency() == CurrencyCode.USD
? retailPrice
: currencyConverter.convert(retailPrice, CurrencyCode.USD);
}
};
}

现在这样写(感觉也没省多少):

 public Comparator<Product> createRetailPriceComparator(
final CurrencyConverter currencyConverter) {
return Comparators.fromFunction(new Function<Product,Money>() {
/** returns the retail price in USD */
public Money apply(Product product) {
Money retailPrice = product.getRetailPrice();
return retailPrice.getCurrency() == CurrencyCode.USD
? retailPrice
: currencyConverter.convert(retailPrice, CurrencyCode.USD);
}
});
}

BiMap(双向map)的用法:
以前的用法:

 private static final Map<Integer, String> NUMBER_TO_NAME;
private static final Map<String, Integer> NAME_TO_NUMBER;
static {
NUMBER_TO_NAME = Maps.newHashMap();
NUMBER_TO_NAME.put(1, "Hydrogen");
NUMBER_TO_NAME.put(2, "Helium");
NUMBER_TO_NAME.put(3, "Lithium");
/* reverse the map programatically so the actual mapping is not repeated */
NAME_TO_NUMBER = Maps.newHashMap();
for (Integer number : NUMBER_TO_NAME.keySet()) {
NAME_TO_NUMBER.put(NUMBER_TO_NAME.get(number), number);
}
}
public static int getElementNumber(String elementName) {
return NUMBER_TO_NAME.get(elementName);
}
public static string getElementName(int elementNumber) {
return NAME_TO_NUMBER.get(elementNumber);
}

现在的用法:

 private static final BiMap<Integer,String> NUMBER_TO_NAME_BIMAP;
static {
NUMBER_TO_NAME_BIMAP = Maps.newHashBiMap();
NUMBER_TO_NAME_BIMAP.put(1, "Hydrogen");
NUMBER_TO_NAME_BIMAP.put(2, "Helium");
NUMBER_TO_NAME_BIMAP.put(3, "Lithium");
}
public static int getElementNumber(String elementName) {
return NUMBER_TO_NAME_BIMAP.inverse().get(elementName);
}
public static string getElementName(int elementNumber) {
return NUMBER_TO_NAME_BIMAP.get(elementNumber);
}

换一种写法:

 private static final BiMap<Integer,String> NUMBER_TO_NAME_BIMAP
= new ImmutableBiMapBuilder<Integer,String>()
.put(1, "Hydrogen")
.put(2, "Helium")
.put(3, "Lithium")
.getBiMap();

关于Strings的一些用法(http://blog.ralscha.ch/?p=888):

assertEquals("test", Strings.emptyToNull("test"));
assertEquals(" ", Strings.emptyToNull(" "));
assertNull(Strings.emptyToNull(""));
assertNull(Strings.emptyToNull(null));
assertFalse(Strings.isNullOrEmpty("test"));
assertFalse(Strings.isNullOrEmpty(" "));
assertTrue(Strings.isNullOrEmpty(""));
assertTrue(Strings.isNullOrEmpty(null));
assertEquals("test", Strings.nullToEmpty("test"));
assertEquals(" ", Strings.nullToEmpty(" "));
assertEquals("", Strings.nullToEmpty(""));
assertEquals("", Strings.nullToEmpty(null));
assertEquals("Ralph_____", Strings.padEnd("Ralph", 10, '_'));
assertEquals("Bob_______", Strings.padEnd("Bob", 10, '_'));
assertEquals("_____Ralph", Strings.padStart("Ralph", 10, '_'));
assertEquals("_______Bob", Strings.padStart("Bob", 10, '_'));
assertEquals("xyxyxyxyxy", Strings.repeat("xy", 5));

Throwables的用法(将检查异常转换成未检查异常):

package com.ociweb.jnb.apr2010;
import com.google.common.base.Throwables;
import java.io.InputStream;
import java.net.URL;
public class ExerciseThrowables {
public static void main(String[] args) {
try {
URL url = new URL("http://ociweb.com");
final InputStream in = url.openStream();
// read from the input stream
in.close();
} catch (Throwable t) {
throw Throwables.propagate(t);
}
}
}

Multimap用法整理(http://jnb.ociweb.com/jnb/jnbApr2008.html):
用来统计多值出现的频率:

        Multimap<Integer, String> siblings = Multimaps.newHashMultimap();
siblings.put(0, "Kenneth");
siblings.put(1, "Joe");
siblings.put(2, "John");
siblings.put(3, "Jerry");
siblings.put(3, "Jay");
siblings.put(5, "Janet");
for (int i = 0; i < 6; i++) {
int freq = siblings.get(i).size();
System.out.printf("%d siblings frequency %d\n", i, freq);
}

输出结果:

Functions(闭包功能)

        Function<String, Integer> strlen = new Function<String, Integer>() {
public Integer apply(String from) {
Preconditions.checkNotNull(from);
return from.length();
}
};
List<String> from = Lists.newArrayList("abc", "defg", "hijkl");
List<Integer> to = Lists.transform(from, strlen);
for (int i = 0; i < from.size(); i++) {
System.out.printf("%s has length %d\n", from.get(i), to.get(i));
}
}

不过这种转换是在访问元素的时候才进行, 下面的例子可以说明:

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