Google Guava 库用法整理_JAVA_编程开发_程序员俱乐部

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

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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:?

Java代码? ?

1. 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):?

Java代码? ?

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

针对不可变集合:?
以前这么用:?

Java代码? ?

1. List<String>?list?=?new?ArrayList<String>();??
2. list.add("a");??
3. list.add("b");??
4. list.add("c");??
5. list.add("d");??

现在Guava这么用:?

Java代码? ?

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

文本文件读取现在Guava这么用?

Java代码? ?

1. File?file?=?new?File(getClass().getResource("/test.txt").getFile());??
2. List<String>?lines?=?null;??
3. try?{??
4. lines?=?Files.readLines(file,?Charsets.UTF_8);??
5. }?catch?(IOException?e)?{??
6. e.printStackTrace();??
7. }??

基本类型比较, 现在Guava这么用:?

Java代码? ?

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

Guava中CharMatcher的用法:?

Java代码? ?

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

Guava中Joiner的用法:?

Java代码? ?

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

另一种写法:?

Java代码? ?

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

Guava中Splitter的用法:?

Java代码? ?

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

对于这样的字符串进行切分:?

Java代码? ?

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

Ints中一些用法:?

Java代码? ?

1. int[]?array?=?{?1,?2,?3,?4,?5?};??
2. int?a?=?4;??
3. boolean?contains?=?Ints.contains(array,?a);??
4. int?indexOf?=?Ints.indexOf(array,?a);??
5. int?max?=?Ints.max(array);??
6. int?min?=?Ints.min(array);??
7. 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)?

Java代码? ?

1. HashSet?setA?=?newHashSet(1,?2,?3,?4,?5);??
2. HashSet?setB?=?newHashSet(4,?5,?6,?7,?8);??
3. ???
4. SetView?union?=?Sets.union(setA,?setB);??
5. System.out.println("union:");??
6. for?(Integer?integer?:?union)??
7. ????System.out.println(integer);?????????
8. ???
9. SetView?difference?=?Sets.difference(setA,?setB);??
10. System.out.println("difference:");??
11. for?(Integer?integer?:?difference)??
12. ????System.out.println(integer);????????
13. ???
14. SetView?intersection?=?Sets.intersection(setA,?setB);??
15. System.out.println("intersection:");??
16. for?(Integer?integer?:?intersection)??
17. ????System.out.println(integer);??

针对Map的用法:?

Java代码? ?

1. MapDifference?differenceMap?=?Maps.difference(mapA,?mapB);??
2. ??
3. differenceMap.areEqual();??
4. Map?entriesDiffering?=?differenceMap.entriesDiffering();??
5. Map?entriesOnlyOnLeft?=?differenceMap.entriesOnlyOnLeft();??
6. Map?entriesOnlyOnRight?=?differenceMap.entriesOnlyOnRight();??
7. Map?entriesInCommon?=?differenceMap.entriesInCommon();??

验证与条件检查?
原来的写法:?

Java代码? ?

1. if?(count?<=?0)?{???????????????????????????????????????????????????????????????????????????????????????????
2. ????throw?new?IllegalArgumentException("must?be?positive:?"?+?count);?????????
3. }????
4. ??????

????????????
Guava的写法(Jakarta Commons中有类似的方法):?

Java代码? ?

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

一个更酷的用法:?

Java代码? ?

1. public?PostExample(final?String?title,?final?Date?date,?final?String?author)?{??
2. ????this.title?=?checkNotNull(title);??
3. ????this.date?=?checkNotNull(date);??
4. ????this.author?=?checkNotNull(author);??
5. }??

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:?

Java代码? ?

1. 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:?

Java代码? ?

1. 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?

Java代码? ?

1. Multimap<String,?Map<String,?String>>?partitionedMap?=?Multimaps.index(?????
2. ????????????????listOfMaps,?????????????????????????????????????????????????????????????????????????????????????????
3. ????????????????new?Function<Map<String,?String>,?String>()?{???????????????????????????????????
4. ????????????????????public?String?apply(final?Map<String,?String>?from)?{??????????????????????
5. ????????????????????????return?from.get("type");???????????????????????????????????????????????????????????????
6. ????????????????????}?????????????????????????????????????????????????????????????????????????????????????????????????????
7. ????????????????});???

?????????????????????????????????????????????????????????????????????????????????????????????????????
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:?

Java代码? ?

1. public?boolean?equals(Object?o)?{??
2. ??if?(o?instanceof?Order)?{??
3. ????Order?that?=?(Order)o;??
4. ??
5. ????return?Objects.equal(address,?that.address)??
6. ????????&&?Objects.equal(targetArrivalDate,?that.targetArrivalDate)??
7. ????????&&?Objects.equal(lineItems,?that.lineItems);??
8. ??}?else?{??
9. ????return?false;??
10. ??}??
11. }??
12. ??
13. public?int?hashCode()?{??
14. ??return?Objects.hashCode(address,?targetArrivalDate,?lineItems);??
15. }??

ImmutableList.copyOf的用法:?
以前这么用:?

Java代码? ?

1. public?Directions(Address?from,?Address?to,?List<Step>?steps)?{??
2. ??this.from?=?from;??
3. ??this.to?=?to;??
4. ??this.steps?=?Collections.unmodifiableList(new?ArrayList<Step>(steps));??
5. }??

现在这么用:?

Java代码? ?

1. public?Directions(Address?from,?Address?to,?List<Step>?steps)?{??
2. ??this.from?=?from;??
3. ??this.to?=?to;??
4. ??this.steps?=?ImmutableList.of(steps);??
5. }??

Iterables.concat()的用法:?
以前这么用:?

Java代码? ?

1. public?boolean?orderContains(Product?product)?{??
2. ??List<LineItem>?allLineItems?=?new?ArrayList<LineItem>();??
3. ??allLineItems.addAll(getPurchasedItems());??
4. ??allLineItems.addAll(getFreeItems());??
5. ??
6. ??for?(LineItem?lineItem?:?allLineItems)?{??
7. ????if?(lineItem.getProduct()?==?product)?{??
8. ??????return?true;??
9. ????}??
10. ??}??
11. ??
12. ??return?false;??
13. }??

现在这么用:?

Java代码? ?

1. public?boolean?orderContains(Product?product)?{??
2. ??for?(LineItem?lineItem?:?Iterables.concat(getPurchasedItems(),?getFreeItems()))?{??
3. ????if?(lineItem.getProduct()?==?product)?{??
4. ??????return?true;??
5. ????}??
6. ??}??
7. ??
8. ??return?false;??
9. }??

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:?

Java代码? ?

1. private?final?List<LineItem>?purchases?=?new?ArrayList<LineItem>();??
2. ??
3. /**?
4. ?*?Don't?modify?this!?Instead,?call?{@link?#addPurchase(LineItem)}?to?add?
5. ?*?new?purchases?to?this?order.?
6. ?*/??
7. public?List<LineItem>?getPurchases()?{??
8. ??return?Collections.unmodifiableList(purchases);??
9. }??
10. ??
11. public?void?addPurchase(LineItem?purchase)?{??
12. ??Preconditions.checkState(catalog.isOffered(getAddress(),?purchase.getProduct()));??
13. ??Preconditions.checkState(purchase.getCharge().getUnits()?>?0);??
14. ??purchases.add(purchase);??
15. }??
16. 这么写:??
17. private?final?List<LineItem>?purchases?=?Constraints.constrainedList(??
18. ????new?ArrayList<LineItem>(),??
19. ????new?Constraint<LineItem>()?{??
20. ??????public?void?checkElement(LineItem?element)?{??
21. ????????Preconditions.checkState(catalog.isOffered(getAddress(),?element.getProduct()));??
22. ????????Preconditions.checkState(element.getCharge().getUnits()?>?0);??
23. ??????}??
24. ????});??
25. ??
26. /**?
27. ?*?Returns?the?modifiable?list?of?purchases?in?this?order.?
28. ?*/??
29. public?List<LineItem>?getPurchases()?{??
30. ??return?purchases;??
31. }??

不允许插入空值的Set(Constraints的用法):?

Java代码? ?

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

Multimap的用法(允许多值的map):?
以前这么写:?

Java代码? ?

1. Map<Salesperson,?List<Sale>>?map?=?new?Hashmap<SalesPerson,?List<Sale>>();??
2. ??
3. public?void?makeSale(Salesperson?salesPerson,?Sale?sale)?{??
4. ??List<Sale>?sales?=?map.get(salesPerson);??
5. ??if?(sales?==?null)?{??
6. ????sales?=?new?ArrayList<Sale>();??
7. ????map.put(salesPerson,?sales);??
8. ??}??
9. ??sales.add(sale);??
10. }??

现在这么写:?

Java代码? ?

1. Multimap<Salesperson,?Sale>?multimap???
2. ????=?new?ArrayListMultimap<Salesperson,Sale>();??
3. ??
4. public?void?makeSale(Salesperson?salesPerson,?Sale?sale)?{??
5. ??multimap.put(salesperson,?sale);??
6. }??

以前这么写:?

Java代码? ?

1. public?Sale?getBiggestSale()?{??
2. ??Sale?biggestSale?=?null;??
3. ??for?(List<Sale>?sales?:?map.values())?{??
4. ????Sale?biggestSaleForSalesman??
5. ????????=?Collections.max(sales,?SALE_COST_COMPARATOR);??
6. ????if?(biggestSale?==?null??
7. ????????||?biggestSaleForSalesman.getCharge()?>?biggestSale().getCharge())?{??
8. ??????biggestSale?=?biggestSaleForSalesman;??
9. ????}??
10. ??}??
11. ??return?biggestSale;??
12. }??

现在这么写(需要将map转换成multimap):?

Java代码? ?

1. public?Sale?getBiggestSale()?{??
2. ??return?Collections.max(multimap.values(),?SALE_COST_COMPARATOR);??
3. }??

Joiner的用法:?
以前这样写:?

Java代码? ?

1. public?class?ShoppingList?{??
2. ??private?List<Item>?items?=?...;??
3. ??
4. ??...??
5. ??
6. ??public?String?toString()?{??
7. ????StringBuilder?stringBuilder?=?new?StringBuilder();??
8. ????for?(Iterator<Item>?s?=?items.iterator();?s.hasNext();?)?{??
9. ??????stringBuilder.append(s.next());??
10. ??????if?(s.hasNext())?{??
11. ????????stringBuilder.append("?and?");??
12. ??????}??
13. ????}??
14. ????return?stringBuilder.toString();??
15. ??}??
16. }??

现在这样写:?

Java代码? ?

1. public?class?ShoppingList?{??
2. ?private?List<Item>?items?=?...;??
3. ??
4. ?...??
5. ??
6. ?public?String?toString()?{??
7. ???return?Join.join("?and?",?items);??
8. ?}??
9. }??

Comparators.fromFunction的用法:?
以前这样写:?

Java代码? ?

1. public?Comparator<Product>?createRetailPriceComparator(??
2. ????final?CurrencyConverter?currencyConverter)?{??
3. ??return?new?Comparator<Product>()?{??
4. ????public?int?compare(Product?a,?Product?b)?{??
5. ??????return?getRetailPriceInUsd(a).compareTo(getRetailPriceInUsd(b));??
6. ????}??
7. ????public?Money?getRetailPriceInUsd(Product?product)?{??
8. ??????Money?retailPrice?=?product.getRetailPrice();??
9. ??????return?retailPrice.getCurrency()?==?CurrencyCode.USD??
10. ????????????retailPrice??
11. ??????????:?currencyConverter.convert(retailPrice,?CurrencyCode.USD);??
12. ????}??
13. ??};??
14. }??

现在这样写(感觉也没省多少):?

Java代码? ?

1. public?Comparator<Product>?createRetailPriceComparator(??
2. ????final?CurrencyConverter?currencyConverter)?{??
3. ??return?Comparators.fromFunction(new?Function<Product,Money>()?{??
4. ????/**?returns?the?retail?price?in?USD?*/??
5. ????public?Money?apply(Product?product)?{??
6. ??????Money?retailPrice?=?product.getRetailPrice();??
7. ??????return?retailPrice.getCurrency()?==?CurrencyCode.USD??
8. ????????????retailPrice??
9. ??????????:?currencyConverter.convert(retailPrice,?CurrencyCode.USD);??
10. ????}??
11. ??});??
12. }??

BiMap(双向map)的用法:?
以前的用法:?

Java代码? ?

1. private?static?final?Map<Integer,?String>?NUMBER_TO_NAME;??
2. private?static?final?Map<String,?Integer>?NAME_TO_NUMBER;??
3. ??
4. static?{??
5. ??NUMBER_TO_NAME?=?Maps.newHashMap();??
6. ??NUMBER_TO_NAME.put(1,?"Hydrogen");??
7. ??NUMBER_TO_NAME.put(2,?"Helium");??
8. ??NUMBER_TO_NAME.put(3,?"Lithium");??
9. ????
10. ??/*?reverse?the?map?programatically?so?the?actual?mapping?is?not?repeated?*/??
11. ??NAME_TO_NUMBER?=?Maps.newHashMap();??
12. ??for?(Integer?number?:?NUMBER_TO_NAME.keySet())?{??
13. ????NAME_TO_NUMBER.put(NUMBER_TO_NAME.get(number),?number);??
14. ??}??
15. }??
16. ??
17. public?static?int?getElementNumber(String?elementName)?{??
18. ??return?NUMBER_TO_NAME.get(elementName);??
19. }??
20. ??
21. public?static?string?getElementName(int?elementNumber)?{??
22. ??return?NAME_TO_NUMBER.get(elementNumber);??
23. }??

现在的用法:?

Java代码? ?

1. private?static?final?BiMap<Integer,String>?NUMBER_TO_NAME_BIMAP;??
2. ??
3. static?{??
4. ??NUMBER_TO_NAME_BIMAP?=?Maps.newHashBiMap();??
5. ??NUMBER_TO_NAME_BIMAP.put(1,?"Hydrogen");??
6. ??NUMBER_TO_NAME_BIMAP.put(2,?"Helium");??
7. ??NUMBER_TO_NAME_BIMAP.put(3,?"Lithium");??
8. }??
9. ??
10. public?static?int?getElementNumber(String?elementName)?{??
11. ??return?NUMBER_TO_NAME_BIMAP.inverse().get(elementName);??
12. }??
13. ??
14. public?static?string?getElementName(int?elementNumber)?{??
15. ??return?NUMBER_TO_NAME_BIMAP.get(elementNumber);??
16. }??

换一种写法:?

Java代码? ?

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

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

Java代码? ?

1. assertEquals("test",?Strings.emptyToNull("test"));??
2. assertEquals("?",?Strings.emptyToNull("?"));??
3. assertNull(Strings.emptyToNull(""));??
4. assertNull(Strings.emptyToNull(null));??
5. ???
6. assertFalse(Strings.isNullOrEmpty("test"));??
7. assertFalse(Strings.isNullOrEmpty("?"));??
8. assertTrue(Strings.isNullOrEmpty(""));??
9. assertTrue(Strings.isNullOrEmpty(null));??
10. ???
11. assertEquals("test",?Strings.nullToEmpty("test"));??
12. assertEquals("?",?Strings.nullToEmpty("?"));??
13. assertEquals("",?Strings.nullToEmpty(""));??
14. assertEquals("",?Strings.nullToEmpty(null));??
15. ???
16. assertEquals("Ralph_____",?Strings.padEnd("Ralph",?10,?'_'));??
17. assertEquals("Bob_______",?Strings.padEnd("Bob",?10,?'_'));??
18. ???
19. assertEquals("_____Ralph",?Strings.padStart("Ralph",?10,?'_'));??
20. assertEquals("_______Bob",?Strings.padStart("Bob",?10,?'_'));??
21. ??
22. assertEquals("xyxyxyxyxy",?Strings.repeat("xy",?5));??

Throwables的用法(将检查异常转换成未检查异常):?

Java代码? ?

1. package?com.ociweb.jnb.apr2010;??
2. ??
3. import?com.google.common.base.Throwables;??
4. ??
5. import?java.io.InputStream;??
6. import?java.net.URL;??
7. ??
8. public?class?ExerciseThrowables?{??
9. ????public?static?void?main(String[]?args)?{??
10. ????????try?{??
11. ????????????URL?url?=?new?URL("http://ociweb.com");??
12. ????????????final?InputStream?in?=?url.openStream();??
13. ????????????//?read?from?the?input?stream??
14. ????????????in.close();??
15. ????????}?catch?(Throwable?t)?{??
16. ????????????throw?Throwables.propagate(t);??
17. ????????}??
18. ????}??
19. }??

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

Java代码? ?

1. Multimap<Integer,?String>?siblings?=?Multimaps.newHashMultimap();??
2. siblings.put(0,?"Kenneth");??
3. siblings.put(1,?"Joe");??
4. siblings.put(2,?"John");??
5. siblings.put(3,?"Jerry");??
6. siblings.put(3,?"Jay");??
7. siblings.put(5,?"Janet");??
8. ??
9. for?(int?i?=?0;?i?<?6;?i++)?{??
10. ????int?freq?=?siblings.get(i).size();??
11. ????System.out.printf("%d?siblings?frequency?%d\n",?i,?freq);??
12. }??

输出结果:?

引用 ??????? 0 siblings frequency 1?
??????? 1 siblings frequency 1?
??????? 2 siblings frequency 1?
??????? 3 siblings frequency 2?
??????? 4 siblings frequency 0?
??????? 5 siblings frequency 1

Functions(闭包功能)?

Java代码? ?

1. Function<String,?Integer>?strlen?=?new?Function<String,?Integer>()?{??
2. ????public?Integer?apply(String?from)?{??
3. ????????Preconditions.checkNotNull(from);??
4. ????????return?from.length();??
5. ????}??
6. };??
7. List<String>?from?=?Lists.newArrayList("abc",?"defg",?"hijkl");??
8. List<Integer>?to?=?Lists.transform(from,?strlen);??
9. for?(int?i?=?0;?i?<?from.size();?i++)?{??
10. ????System.out.printf("%s?has?length?%d\n",?from.get(i),?to.get(i));??
11. }??

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:?

Java代码? ?

1. Function<String,?Boolean>?isPalindrome?=?new?Function<String,?Boolean>()?{??
2. ????public?Boolean?apply(String?from)?{??
3. ????????Preconditions.checkNotNull(from);??
4. ????????return?new?StringBuilder(from).reverse().toString().equals(from);??
5. ????}??
6. };??
7. List<String>?from?=?Lists.newArrayList("rotor",?"radar",?"hannah",?"level",?"botox");??
8. List<Boolean>?to?=?Lists.transform(from,?isPalindrome);??
9. for?(int?i?=?0;?i?<?from.size();?i++)?{??
10. ????System.out.printf("%s?is%sa?palindrome\n",?from.get(i),?to.get(i)???"?"?:?"?NOT?");??
11. }???
12. //?changes?in?the?"from"?list?are?reflected?in?the?"to"?list??
13. System.out.printf("\nnow?replace?hannah?with?megan...\n\n");??
14. from.set(2,?"megan");??
15. for?(int?i?=?0;?i?<?from.size();?i++)?{??
16. ????System.out.printf("%s?is%sa?palindrome\n",?from.get(i),?to.get(i)???"?"?:?"?NOT?");??
17. } ?