Expand Authors Top

If you have a few years of experience in the Java ecosystem and you’d like to share that with the community, have a look at our Contribution Guidelines.

Expanded Audience – Frontegg – Security (partner)
announcement - icon User management is very complex, when implemented properly. No surprise here.

Not having to roll all of that out manually, but instead integrating a mature, fully-fledged solution - yeah, that makes a lot of sense.
That's basically what Frontegg is - User Management for your application. It's focused on making your app scalable, secure and enjoyable for your users.
From signup to authentication, it supports simple scenarios all the way to complex and custom application logic.

Have a look:

>> Elegant User Management, Tailor-made for B2B SaaS

Generic Top

Get started with Spring 5 and Spring Boot 2, through the Learn Spring course:

>> CHECK OUT THE COURSE

1. Overview

In this tutorial, we will learn how to use the Joiner and Splitter in the Guava library. We'll convert collections into a String with the Joiner and we'll split a String into a collection with the Splitter.

2. Convert List into String Using Joiner

Let's start with a simple example to join a List into a String using Joiner. In the following example, we join a List of names into one String using the comma “,” as a separator:

@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");
}

3. Convert Map to String Using Joiner

Next – let's see how to use Joiner to convert a Map to a String. In the following example, we use withKeyValueSeparator() to join the key with its value:

@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"));
}

4. Join Nested Collections

Now – let's see how to join nested collections into a String. In the following example, we join the result of transforming each List to a String:

@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("John-Jane-Adam"));
}

5. Handle Null Values While Using Joiner

Now – let's see different ways to Handle Null Values While Using Joiner.

To skip null values while joining collection use skipNulls() as in the following example:

@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");
}

If you don't want to skip null values and want to replace them instead, use useForNull() as in the following example:

@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");
}

Note that useForNull() doesn't change the original list, it only affect the output of the join.

6. Create List From String Using Splitter

Now – let's see how to split a String into a List. In the following example, we use “-” separator to split the input String to List:

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

    assertThat(result, contains("apple", "banana", "orange"));
}

Note that trimResults() removes the leading and trailing whitespace from the resulting substrings.

7. Create Map From String Using Splitter

Next – let's see how Create Map from String Using Splitter. In the following example, we use withKeyValueSeparator() to split a String into a Map:

@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"));
}

8. Split String With Multiple Separators

Now – let's see how to split a String with multiple separators. In the following example, we use both “.” and “,” to split our String:

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

    assertThat(result, contains("apple", "banana", "orange"));
}

Note that omitEmptyStrings() ignores empty strings and doesn't add them to the resulting List.

9. Split a String at Specific Length

Next – let's take a look on splitting a String at specific length. In the following example, we split our String every 3 characters:

@Test
public void whenSplitStringOnSpecificLength_thenSplit() {
    String input = "Hello world";
    List<String> result = Splitter.fixedLength(3).splitToList(input);

    assertThat(result, contains("Hel", "lo ", "wor", "ld"));
}

10. Limit the Split Result

Finally – let's see how to Limit the Split Result. If you want the Splitter to stop splitting after specific number of items – use limit() as in the following example:

@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"));
}

11. Conclusion

In this tutorial we illustrated how to use both the Joiner and Splitter in Guava to do a variety of transformations between collections and Strings.

The implementation of all these examples and code snippets can be found in my Guava github project – this is an Eclipse based project, so it should be easy to import and run as it is.

Generic bottom

Get started with Spring 5 and Spring Boot 2, through the Learn Spring course:

>> CHECK OUT THE COURSE
Generic footer banner
Comments are closed on this article!