Java的jLinqer包介绍

1.介绍

熟悉C#的lambda 表达式，想要使用 LINQ 在 Java，是个问题，虽然 Java8用函数式接口已经实现了部分lambda 表达式，但是还是不够灵活。



2.Linqer简介

Linqer 是在 Java 中的可以使用 LINQ 语言集成查询 (LINQ)。可以弥补目前Java8在 LINQ方面的一些不足，实现了在 c# 中 的(selectMany，Union, Intersect, Except等)。
 
3.使用方法
 
如果你使用 Maven，请在以下 pom.xml 应用以下包。
<dependency>
    <groupId>com.github.jlinqer</groupId>
    <artifactId>jlinqer</artifactId>
    <version>1.0.0</version>
</dependency>

如果没有使用Maven 时，直接使用 jLinqer jar，下载地址：

https://oss.sonatype.org/content/groups/public/com/github/jlinqer/jlinqer/1.0.0/jlinqer-1.0.0.jar

 

4.LINQ jLinqer 对比

 

功能LINQ(C#)jLinqer(Java)Stream(Java)
【基本】      
筛选 Where where filter
投影 Select select map
排序（升序） OrderBy orderBy sorted
排序（降序） OrderByDescending orderByDescending n/a
按升序对序列中的元素执行后续排序 ThenBy thenBy n/a
按降序对序列中的元素执行后续排序。 ThenByDescending thenByDescending n/a
将序列的每个元素投影到 IEnumerable<T> 并将结果序列合并为一个序列。 SelectMany selectMany flatMap
【提取】      
跳过序列中指定数量的元素，然后返回剩余的元素。 Skip skip skip
只要满足指定的条件，就跳过序列中的元素，然后返回剩余元素。 SkipWhile skipWhile n/a
从序列的开头返回指定数量的连续元素。 Take take limit
只要满足指定的条件，就会返回序列的元素，然后跳过剩余的元素。 TakeWhile takeWhile n/a
【合成】      
连接两个序列 Concat concat concat
生成两个序列的交集 Intersect intersect n/a
生成两个序列的并集 Union union n/a
生成两个序列的差集 Except except n/a
基于匹配键对两个序列的元素进行关联 Join join n/a
基于键相等对两个序列的元素进行关联并对结果进行分组 GroupJoin groupJoin n/a
反转序列中元素的顺序 Reverse reverse n/a
将指定函数应用于两个序列的对应元素，以生成结果序列 Zip zip n/a
【分组和总计】      
返回序列中的非重复元素 Distinct distinct distinct
累加器函数 Aggregate aggregate reduce
对序列中的元素进行分组 GroupBy groupBy Collectors.groupingBy
计算数值序列的平均值 Average averageXXX Collectors.summarizingXXX
返回序列中的元素数量 Count count n/a
返回一个 Int64，表示序列中的元素的数量 LongCount longCount count
返回值序列中的最大值 Max max max
返回值序列中的最小值 Min min min
计算数值序列之和 Sum sumXXX Collectors.summarizingXXX
返回序列中的第一个元素 First first findFirst
返回序列中的第一个元素；如果未找到元素，则返回默认值 FirstOrDefault firstOrDefault n/a
返回序列的最后一个元素 Last last n/a
返回序列中的最后一个元素；如果未找到元素，则返回默认值 LastOrDefault lastOrDefault n/a
返回值序列的单个特定元素 Single single n/a
返回序列中单个特定元素，如果未找到这样的元素，则返回默认值 SingleOrDefault singleOrDefault n/a
返回指定序列的元素；如果序列为空，则返回集合中的类型参数的默认值。 DefaultIfEmpty defaultIfEmpty n/a
返回序列中指定索引处的元素 ElementAt elementAt n/a
返回序列中指定索引处的元素；如果索引超出范围，则返回默认值 ElementAtOrDefault elementAtOrDefault n/a
确定序列中的所有元素是否满足条件 All all allMatch
确定序列中的任何元素是否存在或满足条件 Any any anyMatch
【区间】      
返回一个具有指定的类型参数的空 Empty empty n/a
生成指定范围内的整数的序列 Range range n/a
生成包含一个重复值的序列 Repeat repeat n/a
【其他】      
根据相等比较器确定两个序列是否相等 SequenceEqual sequenceEqual n/a
强制转换为指定的类型 Cast cast n/a
根据指定类型筛选 IEnumerable 的元素 OfType ofType n/a

 

5.使用方法

Where

1 List<Integer> list = new List<>(1, 2, 3);
2 
3 List<Integer> actual = list.where(x -> x == 1 || x == 3).toList();
4 
5 assertEquals(true , actual.contains(1));
6 assertEquals(false, actual.contains(2));
7 assertEquals(true , actual.contains(3));

 

Select

 1 List<Person> list = new List<>(
 2 new Person("React" , 1),
 3 new Person("Angular" , 3),
 4 new Person("Backbone", 5)
 5 );
 6 
 7 List<String> actual = list.select(x -> x.name).toList();
 8 
 9 assertEquals("React" , actual.get(0));
10 assertEquals("Angular" , actual.get(1));
11 assertEquals("Backbone", actual.get(2));

 

OrderBy

1 List<String> list = new List<>("Backbone", "Angular", "React");
2 
3 List<String> actual = list.orderBy(x -> x).toList();
4 
5 assertEquals("Angular" , actual.get(0));
6 assertEquals("Backbone", actual.get(1));
7 assertEquals("React" , actual.get(2));

 

OrderByDescending

1 List<String> list = new List<>("Backbone", "Angular", "React");
2 
3 List<String> actual = list.orderByDescending(x -> x).toList();
4 
5 assertEquals("React" , actual.get(0));
6 assertEquals("Backbone", actual.get(1));
7 assertEquals("Angular" , actual.get(2));

 

ThenBy

 1 List<Person> list = new List<>(
 2 new Person("Angular2", 2),
 3 new Person("Angular1", 2),
 4 new Person("React" , 1)
 5 );
 6 
 7 List<String> actual = list.orderBy(x -> x.age).thenBy(x -> x.name).toList();
 8 
 9 assertEquals("React" , actual.get(0).name);
10 assertEquals("Angular1", actual.get(1).name);
11 assertEquals("Angular2" , actual.get(2).name);

 

ThenByDescending

 1 List<Person> list = new List<>(
 2 new Person("Angular2", 2),
 3 new Person("Angular1", 2),
 4 new Person("React" , 1)
 5 );
 6 
 7 List<String> actual = list.orderBy(x -> x.age).thenByDescending(x -> x.name).toList();
 8 
 9 assertEquals("React" , actual.get(0).name);
10 assertEquals("Angular2", actual.get(1).name);
11 assertEquals("Angular1" , actual.get(2).name);

 

SelectMany

 1 List<Person> list = new List<>(
 2 new Person("Angular", 3, new List("1.0.1", "1.0.2")),
 3 new Person("React" , 1, new List("2.0.1", "2.0.2"))
 4 );
 5 
 6 List<String> actual = list.selectMany(x -> x.versionHistory).toList();
 7 
 8 assertEquals("1.0.1", actual.get(0));
 9 assertEquals("1.0.2", actual.get(1));
10 assertEquals("2.0.1", actual.get(2));
11 assertEquals("2.0.2", actual.get(3));

 

Skip

1 List<Integer> list = new List<>(1, 2, 3);
2 
3 List<Integer> actual = list.skip(2).toList();
4 
5 assertEquals(3, actual.get(0).intValue());

 

SkipWhile

1 List<Integer> list = new List<>(1, 2, 3, 4, 5);
2 
3 List<Integer> actual = list.skipWhile(x -> x <= 3).toList();
4 
5 assertEquals(4, actual.get(0).intValue());
6 assertEquals(5, actual.get(1).intValue());

 

Take

1 List<String> list = new List<>("Backbone", "Angular", "React");
2 
3 List<String> actual = list.take(2).toList();
4 
5 assertEquals(2, actual.size());
6 assertEquals("Backbone", actual.get(0));
7 assertEquals("Angular" , actual.get(1));

 

TakeWhile

1 List<String> list = new List<>("Backbone", "Angular", "React");
2 
3 List<String> actual = list.takeWhile(x -> x.equals("Backbone") || x.equals("Angular")).toList();
4 
5 assertEquals(2, actual.size());
6 assertEquals("Backbone", actual.get(0));
7 assertEquals("Angular" , actual.get(1));

 

Concat

1 List<Integer> first = new List<>(1, 2);
2 List<Integer> second = new List<>(2, 3);
3 
4 List<Integer> actual = first.concat(second).toList();
5 
6 assertEquals(1, actual.get(0).intValue());
7 assertEquals(2, actual.get(1).intValue());
8 assertEquals(2, actual.get(2).intValue());
9 assertEquals(3, actual.get(3).intValue());

 

Intersect

1 List<Integer> first = new List<>(1, 2, 3);
2 List<Integer> second = new List<>(1, 3);
3 
4 List<Integer> actual = first.intersect(second).toList();
5 
6 assertEquals(1, actual.get(0).intValue());
7 assertEquals(3, actual.get(1).intValue());

 

Union

 1 List<Integer> first = new List<>(1, 2, 3);
 2 List<Integer> second = new List<>(0, 1, 3, 4);
 3 
 4 List<Integer> actual = first.union(second).toList();
 5 
 6 assertEquals(5, actual.size());
 7 assertEquals(1, actual.get(0).intValue());
 8 assertEquals(2, actual.get(1).intValue());
 9 assertEquals(3, actual.get(2).intValue());
10 assertEquals(0, actual.get(3).intValue());
11 assertEquals(4, actual.get(4).intValue());

 

Except

1 List<Integer> first = new List<>(1, 2, 3);
2 List<Integer> second = new List<>(1, 3);
3 
4 List<Integer> actual = first.except(second).toList();
5 
6 assertEquals(2, actual.get(0).intValue());

 

Join

 1 List<Javascript> outer = new List<>(
 2 new Javascript("Angular", 1),
 3 new Javascript("React" , 4),
 4 new Javascript("ES2016" , 5)
 5 );
 6 List<Javascript> inner = new List<>(
 7 new Javascript("Angular", 2),
 8 new Javascript("Angular", 3),
 9 new Javascript("ES2016" , 6),
10 new Javascript("ES7" , 7)
11 );
12 
13 Function<Javascript, String> outerKey = (x) -> x.name;
14 Function<Javascript, String> innerKey = (y) -> y.name;
15 BiFunction<Javascript, Javascript, Javascript> selector = (x, y) -> new Javascript(x.name, y.age);
16 List<Javascript> actual = outer.join(inner, outerKey, innerKey, selector).toList();
17 
18 assertEquals(3, actual.size());
19 assertEquals("Angular", actual.get(0).name);
20 assertEquals("Angular", actual.get(1).name);
21 assertEquals("ES2016" , actual.get(2).name);
22 assertEquals(2, actual.get(0).age);
23 assertEquals(3, actual.get(1).age);
24 assertEquals(6, actual.get(2).age);

 

GroupJoin

 1 List<Javascript> outer = new List<>(
 2 new Javascript("Angular", 1),
 3 new Javascript("React" , 4),
 4 new Javascript("ES2016" , 5)
 5 );
 6 List<Javascript> inner = new List<>(
 7 new Javascript("Angular", 2),
 8 new Javascript("Angular", 3),
 9 new Javascript("ES2016" , 6),
10 new Javascript("ES7" , 7)
11 );
12 
13 Function<Javascript, String> outerKey = (x) -> x.name;
14 Function<Javascript, String> innerKey = (y) -> y.name;
15 BiFunction<Javascript, IEnumerable<Javascript>, Javascript> selector = (x, y) -> new Javascript(x.name, y.select(z -> z.age));
16 List<Javascript> actual = outer.groupJoin(inner, outerKey, innerKey, selector).toList();
17 
18 assertEquals(3, actual.size());
19 assertEquals("Angular", actual.get(0).name);
20 assertEquals("React" , actual.get(1).name);
21 assertEquals("ES2016" , actual.get(2).name);
22 assertEquals(2, actual.get(0).ages.elementAt(0));
23 assertEquals(3, actual.get(0).ages.elementAt(1));
24 assertEquals(0, actual.get(1).ages.count());
25 assertEquals(6, actual.get(2).ages.elementAt(0));

 

Reverse

1 List<Integer> list = new List<>(1, 2, 3);
2 
3 List<Integer> actual = list.reverse().toList();
4 
5 assertEquals(3, actual.get(0).intValue());
6 assertEquals(2, actual.get(1).intValue());
7 assertEquals(1, actual.get(2).intValue());

 

Zip

1 List<Integer> first = new List<>(1, 2, 3);
2 List<String> second = new List<>("Angular", "React", "Backbone");
3 
4 List<Integer> actual = first.zip(second, (x, y) -> String.format("%s %d", x, y)).toList();
5 
6 assertEquals("1 Angular" , actual.get(0));
7 assertEquals("2 React" , actual.get(1));
8 assertEquals("3 Backbone", actual.get(2));

 

Distinct

1 List<Integer> list =new List<>(1, 2, 3,1, 2, 3, 4);
2 
3 List<Integer> actual = list.distinct().toList();
4 
5 assertEquals(1, actual.get(0).intValue());
6 assertEquals(2, actual.get(1).intValue());
7 assertEquals(3, actual.get(2).intValue());
8 assertEquals(4, actual.get(3).intValue());

 

Aggregate

1 List<Integer> list = new List<>(1, 2, 3);
2 
3 int actual = list.aggregate((sum, elem) -> sum + elem);
4 
5 assertEquals(6, actual);

 

GroupBy

 1 List<Person> list = new List<>(
 2 new Person("React" , 1),
 3 new Person("Angular" , 1),
 4 new Person("Backbone", 5)
 5 );
 6 
 7 Map<Integer, IEnumerable<Person>> actual = list.groupBy(x -> x.age);
 8 
 9 assertEquals(true, actual.get(1).any(x -> x.name.equals("React")));
10 assertEquals(true, actual.get(1).any(x -> x.name.equals("Angular")));
11 assertEquals(true, actual.get(5).any(x -> x.name.equals("Backbone")));

 

Average

1 List<Long> listLong = new List<>(1l, 2l, 3l, 4l);
2 
3 double actualLong = listLong.averageLong(x -> x);
4 
5 assertEquals(2.5d, actualLong, 0);

 

Count

1 List<String> list = new List<>("Backbone", "Angular", "React");
2 
3 long actual = list.longCount();
4 int actualNone = list.count(x -> x.equals("jquery"));
5 
6 assertEquals(3, actual);
7 assertEquals(0, actualNone);

 

Max

1 List<Double> listDouble = new List<>(1d, 2d, 3d);
2 
3 double actualDouble = listDouble.max(x -> x);
4 
5 assertEquals(3d, actualDouble, 0);

 

Min

1 List<BigDecimal> listBigDecimal = new List<>(
2 new BigDecimal(1d),
3 new BigDecimal(2d),
4 new BigDecimal(3d)
5 );
6 
7 BigDecimal actualBigDecimal = listBigDecimal.min(x -> x);
8 
9 assertEquals(1d, actualBigDecimal.doubleValue(), 0);

 

Sum

1 List<Integer> listInt = new List<>(1, 2, 3);
2 
3 int actualInt = listInt.sumInt(x -> x);
4 
5 assertEquals(6, actualInt);

 

FirstOrDefault

1 List<String> list = new List<>("Backbone", "Angular", "React");
2 
3 String actualFirst = list.firstOrDefault();
4 String actualMatch = list.firstOrDefault(x -> x.equals("Angular"));
5 String actualUnMatch = list.firstOrDefault(x -> x.equals("jquery"));
6 
7 assertEquals("Backbone", actualFirst);
8 assertEquals("Angular" , actualMatch);
9 assertEquals(null , actualUnMatch);

 

LastOrDefault

1 List<Integer> list = new List<>(1, 2, 3);
2 List<Integer> listEmpty = new List<>();
3 
4 int actual = list.lastOrDefault();
5 Integer actualDefaultNone = listEmpty.lastOrDefault(x -> x == 0);
6 
7 assertEquals(3, actual);
8 assertEquals(null, actualDefaultNone);

 

SingleOrDefault

1 List<Integer> listMany = new List<>(1, 2, 3);
2 List<Integer> listEmpty = new List<>();
3 
4 int actualFilter = listMany.singleOrDefault(x -> x == 3);
5 Integer actualUnMatch = listEmpty.singleOrDefault(x -> x == 0);
6 
7 assertEquals(3, actualFilter);
8 assertEquals(null, actualUnMatch);

 

DefaultIfEmpty

 1 List<String> listEmpty = new List<>();
 2 
 3 List<String> actualDefault = listEmpty.defaultIfEmpty("ES7").toList();
 4 
 5 assertEquals("ES7", actualDefault.get(0));
 6 ElementAtOrDefault
 7 
 8 List<Integer> list = new List<>(1, 2, 3);
 9 
10 int actual = list.elementAtOrDefault(2);
11 Integer actualDefault = list.elementAtOrDefault(3);
12 
13 assertEquals(3, actual);
14 assertEquals(null, actualDefault);

 

All

1 List<String> list = new List<>("Backbone", "Angular", "React");
2 
3 boolean actual = list.all(x -> x.equals("Angular") || x.equals("Backbone") || x.equals("React"));
4 boolean actualNotFound = list.all(x -> x.equals("Angular") || x.equals("React"));
5 
6 assertEquals(true, actual);
7 assertEquals(false, actualNotFound);

 

Any

1 List<String> list = new List<>("Backbone", "Angular", "React");
2 
3 boolean actual = list.any(x -> x.equals("Angular"));
4 boolean actualNotFound = list.any(x -> x.equals("jquery"));
5 
6 assertEquals(true, actual);
7 assertEquals(false, actualNotFound);

 

Empty

1 List<Double> actual = IEnumerable.empty(Double.class);
2 
3 assertEquals(0, actual.count());

 

Range

1 List<Integer> actual = IEnumerable.range(-2, 3);
2 
3 assertEquals(-2, actual.get(0).intValue());
4 assertEquals(-1, actual.get(1).intValue());
5 assertEquals(0 , actual.get(2).intValue());

 

Repeat

 1 List<String> actual = IEnumerable.repeat(String.class, "Law of Cycles", 10);
 2 
 3 assertEquals(10, actual.count());
 4 assertEquals("Law of Cycles", actual.get(9));
 5 SequenceEqual
 6 
 7 List<Integer> first = new List<>(1, 2, 3);
 8 List<Integer> secondMatch = new List<>(1, 2, 3);
 9 List<Integer> secondUnMatchElem = new List<>(1, 2, 4);
10 
11 boolean actualMatch = first.sequenceEqual(secondMatch);
12 boolean actualUnMatchElm = first.sequenceEqual(secondUnMatchElem);
13 
14 assertEquals(true, actualMatch);
15 assertEquals(false, actualUnMatchElm);

 

Cast

1 List<Object> list = new List<>(1, 2, 3);
2 
3 List<Integer> actual = list.cast(Integer.class).toList();
4 
5 assertEquals(1, actual.get(0).intValue());
6 assertEquals(2, actual.get(1).intValue());
7 assertEquals(3, actual.get(2).intValue());

 

OfType

1 List<Object> list = new List<>(1, "2", 3, "4");
2 
3 List<String> actualStr = list.ofType(String.class).toList();
4 List<Integer> actualInt = list.ofType(Integer.class).toList();
5 
6 assertEquals("2", actualStr.get(0));
7 assertEquals("4", actualStr.get(1));
8 assertEquals(1 , actualInt.get(0).intValue());
9 assertEquals(3 , actualInt.get(1).intValue());

 

6.源代码 

https://github.com/k--kato/jLinqer

 

 

posted @ 2015-12-22 01:45  cnkker.com  阅读(628)  评论(0)  编辑  收藏  举报