【Guava 】Collections – Join and Split

Convert Collections to String Using Joiner

Convert List into String Using Joiner

@Test
public void whenConvertListToString_thenConverted() {
    List<String> names = Lists.newArrayList("John", "Jane", "Adam", "Tom");
    String result = Joiner.on(",").join(names);
 
    assertEquals(result, "John,Jane,Adam,Tom");
}

Convert Map to String Using Joiner

@Test
public void whenConvertMapToString_thenConverted() {
    Map<String, Integer> salary = Maps.newHashMap();
    salary.put("John", 1000);
    salary.put("Jane", 1500);
    String result = Joiner.on(" , ").withKeyValueSeparator(" = ")
                                    .join(salary);
 
    assertThat(result, containsString("John = 1000"));
    assertThat(result, containsString("Jane = 1500"));
}

Join Nested Collections

@Test
public void whenJoinNestedCollections_thenJoined() {
    List<ArrayList<String>> nested = Lists.newArrayList(
      Lists.newArrayList("apple", "banana", "orange"),
      Lists.newArrayList("cat", "dog", "bird"),
      Lists.newArrayList("John", "Jane", "Adam"));
    String result = Joiner.on(";").join(Iterables.transform(nested,
      new Function<List<String>, String>() {
          @Override
          public String apply(List<String> input) {
              return Joiner.on("-").join(input);
          }
      }));
 
    assertThat(result, containsString("apple-banana-orange"));
    assertThat(result, containsString("cat-dog-bird"));
    assertThat(result, containsString("apple-banana-orange"));
}

Handle null values while using Joiner

skip null values

@Test
public void whenConvertListToStringAndSkipNull_thenConverted() {
    List<String> names = Lists.newArrayList("John", null, "Jane", "Adam", "Tom");
    String result = Joiner.on(",").skipNulls().join(names);
 
    assertEquals(result, "John,Jane,Adam,Tom");
}

replace them instead

@Test
public void whenUseForNull_thenUsed() {
    List<String> names = Lists.newArrayList("John", null, "Jane", "Adam", "Tom");
    String result = Joiner.on(",").useForNull("nameless").join(names);
 
    assertEquals(result, "John,nameless,Jane,Adam,Tom");
}

---

Create Collections from String using Splitter

Create List from String using Splitter

@Test
public void whenCreateListFromString_thenCreated() {
    String input = "apple - banana - orange";
    List<String> result = Splitter.on("-").trimResults()
                                          .splitToList(input);
 
    assertThat(result, contains("apple", "banana", "orange"));
}

Create Map from String using Splitter

@Test
public void whenCreateMapFromString_thenCreated() {
    String input = "John=first,Adam=second";
    Map<String, String> result = Splitter.on(",")
                                         .withKeyValueSeparator("=")
                                         .split(input);
 
    assertEquals("first", result.get("John"));
    assertEquals("second", result.get("Adam"));
}

---

Split String

Split String with multiple separators

@Test
public void whenSplitStringOnMultipleSeparator_thenSplit() {
    String input = "apple.banana,,orange,,.";
    List<String> result = Splitter.onPattern("[.|,]")
                                  .omitEmptyStrings()
                                  .splitToList(input);
 
    assertThat(result, contains("apple", "banana", "orange"));
}

Split a String at specific length

@Test
public void whenSplitStringOnSpecificLength_thenSplit() {
    String input = "Hello world";
    List<String> result = Splitter.fixedLength(3).splitToList(input);
 
    assertThat(result, contains("Hel", "lo ", "wor", "ld"));
}

Limit the split result

@Test
public void whenLimitSplitting_thenLimited() {
    String input = "a,b,c,d,e";
    List<String> result = Splitter.on(",")
                                  .limit(4)
                                  .splitToList(input);
 
    assertEquals(4, result.size());
    assertThat(result, contains("a", "b", "c", "d,e"));
}

---

參考

Guava – Join and Split Collections