Guava学习笔记--01. Joiner使用

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对于Guava的认识来自于阅读QMQ源码的时候，有很多没有使用过的Java方法和集合，所以就查了查，发现是用的是Guava的类库，所以就有了下面的博客：

1. 字符串的拼接

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private final List<String> stringList = Arrays.asList("Google", "Guava", "Java", "Scala", "Kafka");
private final List<String> stringListWithNullValue = Arrays.asList("Google", "Guava", "Java", "Scala", null);


 //1. 字符串的拼接
@Test
public void Test() {
    String join = Joiner.on("*").join(stringList);
    System.out.println(join);
    assertEquals(join, "Google*Guava*Java*Scala*Kafka");
}

@Test(expected = NullPointerException.class)
public void TestJoinValue() {
    String join = Joiner.on("*").join(stringListWithNullValue);
    System.out.println(join);
    assertEquals(join, "Google*Guava*Java*Scala*Kafka");
}

2. 跳过空数据

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//2. 跳过空数据
@Test
public void TestJoinSkipValue() {
    String join = Joiner.on("*").skipNulls().join(stringListWithNullValue);
    System.out.println(join);
    assertEquals(join, "Google*Guava*Java*Scala");
}

3. 为空的数据指定一个默认值

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 //3. 为空的数据指定一个默认值
@Test
public void TestJoinDefalutValue() {
    String join = Joiner.on("*").useForNull("Defalut").join(stringListWithNullValue);
    System.out.println(join);
    assertEquals(join, "Google*Guava*Java*Scala*Defalut");
}

4. 追加到StringBuilder

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//4. 追加到StringBuilder
@Test
public void TestJoinDefalutValueStringBuffer() {
    StringBuilder stringBuilder = new StringBuilder();
    StringBuilder thatBuilder = Joiner.on("*").useForNull("Defalut").appendTo(stringBuilder, stringListWithNullValue);
    assertThat(thatBuilder, sameInstance(stringBuilder));
    assertThat(stringBuilder.toString(), equalTo("Google*Guava*Java*Scala*Defalut"));
    assertThat(thatBuilder.toString(), equalTo("Google*Guava*Java*Scala*Defalut"));
}

5. 追加到文件

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//5. 追加到文件
@Test
public void TestJoinDefalutValueToWrite() {

    try (FileWriter fileWriter = new FileWriter(new File("1.txt"))) {
        Joiner.on("#").useForNull("Default").appendTo(fileWriter, stringListWithNullValue);
        assert (Files.isFile().test(new File("1.txt")));
    } catch (IOException e) {
        e.printStackTrace();
    }
}

6. 使用Java8实现相同的功能

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//java8
@Test
public void TestJoinDefalutByStream() {
    String result = stringListWithNullValue.stream().map(x -> x == null || x.isEmpty() ? "Defalut" : x).collect(Collectors.joining("*"));
    assertThat(result, equalTo("Google*Guava*Java*Scala*Defalut"));
}

7. 使用Guava对Map进行join

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@Test
public void testJoinOnWithMap(){
     //创建一个map
    Map<String,String> stringMap= ImmutableMap.of("Hello","Guava","Java","Scala"); 
    String join = Joiner.on("#").withKeyValueSeparator("=").join(stringMap);
    System.out.println(join);
    assert join.equals("Hello=Guava#Java=Scala");
}