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Guava: String Manipulation with CharMatcher, Spliter and Joiner

Guava has very simple and powerful string manipulation mechanism. Here are some classes like CharMatcher, Splitter and Joiner provides very simple way to perform some complex operation on string collections.

CharMatcher
Determines a true or false value for any Java char value, just as Predicate does for any Object.[from guava doc]


Use a predefined constant (predefine CharMatcher)
  • CharMatcher.WHITESPACE (Java whitespace character)
  • CharMatcher.JAVA_DIGIT
  • CharMatcher.JAVA_LETTER
  • CharMatcher.JAVA_LOWER_CASE 
  • CharMatcher.JAVA_UPPER_CASE 
  • CharMatcher.ASCII
  • CharMatcher.ANY
  • ...

String str = "FirstName LastName +1 123 456 789 !@#$%^&*()_+|}{:\"?><";

CharMatcher.DIGIT.retainFrom(str);

Output:->
"1123456789"


CharMatcher.JAVA_LETTER.retainFrom(str);

Output:->
"FirstNameLastName"


CharMatcher.JAVA_LETTER_OR_DIGIT.retainFrom(str);

Output:->
"FirstNameLastName1123456789"


CharMatcher.ANY.countIn(str)

Output:->
54


CharMatcher.DIGIT.countIn(str);

Output:->
10



Use a factory method
  • CharMatcher.is('x')
  • CharMatcher.isNot('_')
  • CharMatcher.oneOf("aeiou").negate()
  • CharMatcher.inRange('a', 'z').or(inRange('A', 'Z'))
  • ...

Use Combination
  • CharMatcher and(CharMatcher other) 
  • CharMatcher or(CharMatcher other) 
  • CharMatcher negate() 


String str = "FirstName LastName +1 123 456 789 !@#$%^&*()_+|}{:\"?><";

CharMatcher.JAVA_LOWER_CASE.negate().retainFrom(str);

Output:->
"FN LN +1 123 456 789 !@#$%^&*()_+|}{:\"?><"


CharMatcher.JAVA_DIGIT.or(CharMatcher.anyOf("aeiou")).retainFrom(str);

Output:->
"iaeaae1123456789"




Splitter
An object that divides strings (or other instances of CharSequence) into substrings, by recognizing a separator (a.k.a. "delimiter") which can be expressed as a single character, literal string, regular expression, CharMatcher, or by using a fixed substring length. [from guava doc]

String str = "test1, , test2, test3";
Iterable<String> strArr = Splitter.on(',')
  .trimResults()
  .omitEmptyStrings()
  .split(str);

Output:->
["test1", "test2", "test3"]


String str = "key1: 1; key2: 2  ; key3: 3";
Map<String, String> m = Splitter.on(';')
  .trimResults()
  .withKeyValueSeparator(":")
  .split(str);

Output:->
{key1= 1, key2= 2, key3= 3}


private static final Splitter COMMA_SPLITTER = Splitter.on(',')
       .trimResults()
       .omitEmptyStrings();
COMMA_SPLITTER.split("foo, ,bar, quux,");

Output:->
["foo", "bar", "quux"]




Joiner
An object which joins pieces of text (specified as an array, Iterable, varargs or even a Map) with a separator.
If neither skipNulls() nor useForNull(String) is specified, the joining methods will throw NullPointerException if any given element is null.[from guava doc]

ArrayList<String> strArr1 = Lists.newArrayList(
                         "test1","test2","test3",null,"test4",null,null);

Joiner.on(';')
  .skipNulls()
  .join(strArr1);

Output:->
"test1;test2;test3;test4"


Joiner.on(';')
  .useForNull("_")
  .join(strArr1);

Output:->
"test1;test2;test3;_;test4;_;_"


Joiner can be use for Map
Map<String, String> map = Maps.newHashMap();
map.put("key1", "value1");
map.put("key2", "value2");
map.put("key3", null);
map.put("key4", "value3");
 
Joiner.on(';')
 .useForNull("NULL")
 .withKeyValueSeparator("=")
 .join(map);

Output:->
"key4=value3;key3=NULL;key2=value2;key1=value1"

Advance use-case for joiner
Skip null and trim the result before joining


ArrayList<String> strArr = Lists.newArrayList(
                         " test1","test2 "," test3 ",null,"test4",null,null,"", "  ");
Predicate<String> EMPTY_OR_NULL_FILTER = new Predicate<String>() {
 @Override
 public boolean apply(String str){
  str = Strings.nullToEmpty(str).trim();
  return !Strings.isNullOrEmpty(str);
 }
};

Function<String, String> TRIM_RESULT = new Function<String, String>(){
 @Override
 public String apply(String str){
  return Strings.nullToEmpty(str).trim();
 }
};
  
String joinStr = Joiner.on(';')
 .skipNulls()
 .join(Collections2.transform(Collections2.filter(strArr, EMPTY_OR_NULL_FILTER), TRIM_RESULT));

Output:->
"test1;test2;test3;test4"


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