Skip to main content

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"


Popular posts from this blog

ERROR: Ignored call to 'alert()'. The document is sandboxed, and the 'allow-modals' keyword is not set.

Recently I found this issue while writing code snippet in "JSFiddle". And after searching, found this was happening because of new feature added in "Chrome 46+". But at the same time Chrome doesn't have support for "allow-modals" property in "sandbox" attribute.

Chromium issue for above behavior:
https://codereview.chromium.org/1126253007

To make it work you have to add "allow-scripts allow-modals" in "sandbox" attribute, and use "window.alert" instead of "alert".



<!-- Sandbox frame will execute javascript and show modal dialogs --> <iframe sandbox="allow-scripts allow-modals" src="iframe.html"> </iframe>


Feature added: Block modal dialog inside a sandboxed iframe.
Link: https://www.chromestatus.com/feature/4747009953103872

Feature working Demo page:
https://googlechrome.github.io/samples/block-modal-dialogs-sandboxed-iframe/index.html



CSS Specificity

Many time different CSS rules overlap on one or more element. And some people always get confuse about, which rule will take higher priority then other and why? CSS Specificity is the answer of all these kind of questions.
As the name suggest, the CSS rule which is more specific to the element will take higher priority then other. Means something like “#some_id{}” will always take higher priority then “*{}” universal selector.  And if duplicate rules are define then the last rule will be applied to the element.

The following list of selectors is by increasing specificity:
Type selector (e.g., div) and pseudo-elements in selector (e.g., :after) Class selectors (e.g., .some_class), attributes selectors (e.g., [type=”radio”]) and pseudo-class selector (e.g., :hover) Id selectors (e.g., #some_id)


ID takes higher priority then Class, Type and Universal selector (Note: Universal selector has no effect on specificity, see below special conditions). 



If duplicate rules are given, then last…

Guava: Some useful IO utilities

Guava IO package provides very useful utility classes for input/ouput stream, byte stream, file handling and many more. Here are few example which show case how these utilities can make your code much cleaner, modular and more readable.Copy “InputStream” to “OutputStream InputStream is = CopyStreams.class.getResourceAsStream("test.txt"); OutputStream os = System.out; ByteStreams.copy(is, os);Changing InputStream to “byte[]” InputStream is = CopyStreams.class.getResourceAsStream("test.txt"); byte[] isBytes = ByteStreams.toByteArray(is); // Now if you want to get base64 encoded string then it will be like this String isBase64Str = new sun.misc.BASE64Encoder().encode(isBytes);Combining two files in one File input1 = new File("c:\\testio\\AWords.txt"); File input2 = new File("c:\\testio\\BWords.txt"); File output = new File("c:\\testio\\ABWords.txt"); …