public final class StringUtils extends Object
Operations on String
that are null
safe.
The StringUtils
class defines certain words related to String
handling.
null
""
)' '
, char 32)Character.isWhitespace(char)
String.trim()
StringUtils
handles null
input Strings quietly.
That is to say that a null
input will return null
.
Where a boolean
or int
is being returned details
vary by method.
A side effect of the null
handling is that a
NullPointerException
should be considered a bug in
StringUtils
(except for deprecated methods).
Methods in this class give sample code to explain their operation. The symbol
*
is used to indicate any input including null
.
String
Modifier and Type | Field and Description |
---|---|
static String |
EMPTY
The empty String
"" . |
static int |
INDEX_NOT_FOUND
Represents a failed index search.
|
Modifier and Type | Method and Description |
---|---|
static String |
abbreviate(String str,
int maxWidth)
Abbreviates a String using ellipses.
|
static String |
abbreviate(String str,
int offset,
int maxWidth)
Abbreviates a String using ellipses.
|
static boolean |
containsAny(String str,
char... searchChars)
Checks if the String contains any character in the given
set of characters.
|
static int |
countMatches(String str,
String sub)
Counts how many times the substring appears in the larger String.
|
static String |
defaultIfBlank(String str,
String defaultStr)
Returns either the passed in CharSequence, or if the CharSequence is
whitespace, empty ("") or
null , the value of defaultStr . |
static String |
defaultIfEmpty(String str,
String defaultStr)
Returns either the passed in String, or if the String is
empty or
null , the value of defaultStr . |
static <T> T |
defaultIfNull(T object,
T defaultValue)
Returns a default value if the object passed is
null . |
static String |
defaultString(String str)
Returns either the passed in String, or if the String is
null , an empty String (""). |
static String |
defaultString(String str,
String defaultStr)
Returns either the passed in String, or if the String is
null , the value of defaultStr . |
static boolean |
equals(Object object1,
Object object2)
Compares two objects for equality, where either one or both
objects may be
null . |
static boolean |
isBlank(String str)
Checks if a String is whitespace, empty ("") or null.
|
static boolean |
isEmpty(String str)
Checks if a String is empty ("") or null.
|
static String |
join(Object[] array,
char separator)
Joins the elements of the provided array into a single String
containing the provided list of elements.
|
static String |
join(Object[] array,
char separator,
int startIndex,
int endIndex)
Joins the elements of the provided array into a single String
containing the provided list of elements.
|
static String |
join(Object[] array,
String separator)
Joins the elements of the provided array into a single String
containing the provided list of elements.
|
static String |
join(Object[] array,
String separator,
int startIndex,
int endIndex)
Joins the elements of the provided array into a single String
containing the provided list of elements.
|
static <T> String |
join(T... elements)
Joins the elements of the provided array into a single String
containing the provided list of elements.
|
static String |
leftPad(String str,
int size)
Left pad a String with spaces (' ').
|
static String |
leftPad(String str,
int size,
char padChar)
Left pad a String with a specified character.
|
static String |
leftPad(String str,
int size,
String padStr)
Left pad a String with a specified String.
|
static String |
replace(String text,
String searchString,
String replacement)
Replaces all occurrences of a String within another String.
|
static String |
replace(String text,
String searchString,
String replacement,
int max)
Replaces a String with another String inside a larger String,
for the first
max values of the search String. |
static String |
replaceEach(String text,
String[] searchList,
String[] replacementList)
Replaces all occurrences of Strings within another String.
|
static String |
rightPad(String str,
int size)
Right pad a String with spaces (' ').
|
static String |
rightPad(String str,
int size,
char padChar)
Right pad a String with a specified character.
|
static String |
rightPad(String str,
int size,
String padStr)
Right pad a String with a specified String.
|
static String[] |
split(String regex,
CharSequence input)
A custom adaptation of
Pattern.split(CharSequence, int) . |
static String |
toCamelCase(String string)
Convert a string to camel case
|
static String |
toCamelCaseLC(String string)
Convert a string to camel case starting with a lower case letter
|
static String |
toLC(String string)
Change a string's first letter to lower case
|
public static final String EMPTY
""
.public static final int INDEX_NOT_FOUND
public static String defaultString(String str)
Returns either the passed in String, or if the String is
null
, an empty String ("").
StringUtils.defaultString(null) = "" StringUtils.defaultString("") = "" StringUtils.defaultString("bat") = "bat"
str
- the String to check, may be nullnull
String.valueOf(Object)
public static String defaultString(String str, String defaultStr)
Returns either the passed in String, or if the String is
null
, the value of defaultStr
.
StringUtils.defaultString(null, "NULL") = "NULL" StringUtils.defaultString("", "NULL") = "" StringUtils.defaultString("bat", "NULL") = "bat"
str
- the String to check, may be nulldefaultStr
- the default String to return
if the input is null
, may be nullnull
String.valueOf(Object)
public static String defaultIfEmpty(String str, String defaultStr)
Returns either the passed in String, or if the String is
empty or null
, the value of defaultStr
.
StringUtils.defaultIfEmpty(null, "NULL") = "NULL" StringUtils.defaultIfEmpty("", "NULL") = "NULL" StringUtils.defaultIfEmpty("bat", "NULL") = "bat"
str
- the String to check, may be nulldefaultStr
- the default String to return
if the input is empty ("") or null
, may be nulldefaultString(String, String)
public static String defaultIfBlank(String str, String defaultStr)
Returns either the passed in CharSequence, or if the CharSequence is
whitespace, empty ("") or null
, the value of defaultStr
.
StringUtils.defaultIfBlank(null, "NULL") = "NULL" StringUtils.defaultIfBlank("", "NULL") = "NULL" StringUtils.defaultIfBlank(" ", "NULL") = "NULL" StringUtils.defaultIfBlank("bat", "NULL") = "bat" StringUtils.defaultIfBlank("", null) = null
str
- the CharSequence to check, may be nulldefaultStr
- the default CharSequence to return
if the input is whitespace, empty ("") or null
, may be nulldefaultString(String, String)
public static boolean isEmpty(String str)
Checks if a String is empty ("") or null.
StringUtils.isEmpty(null) = true StringUtils.isEmpty("") = true StringUtils.isEmpty(" ") = false StringUtils.isEmpty("bob") = false StringUtils.isEmpty(" bob ") = false
NOTE: This method changed in Lang version 2.0. It no longer trims the String. That functionality is available in isBlank().
str
- the String to check, may be nulltrue
if the String is empty or nullpublic static boolean isBlank(String str)
Checks if a String is whitespace, empty ("") or null.
StringUtils.isBlank(null) = true StringUtils.isBlank("") = true StringUtils.isBlank(" ") = true StringUtils.isBlank("bob") = false StringUtils.isBlank(" bob ") = false
str
- the String to check, may be nulltrue
if the String is null, empty or whitespacepublic static int countMatches(String str, String sub)
Counts how many times the substring appears in the larger String.
A null
or empty ("") String input returns 0
.
StringUtils.countMatches(null, *) = 0 StringUtils.countMatches("", *) = 0 StringUtils.countMatches("abba", null) = 0 StringUtils.countMatches("abba", "") = 0 StringUtils.countMatches("abba", "a") = 2 StringUtils.countMatches("abba", "ab") = 1 StringUtils.countMatches("abba", "xxx") = 0
str
- the String to check, may be nullsub
- the substring to count, may be nullnull
public static String rightPad(String str, int size)
Right pad a String with spaces (' ').
The String is padded to the size of size
.
StringUtils.rightPad(null, *) = null StringUtils.rightPad("", 3) = " " StringUtils.rightPad("bat", 3) = "bat" StringUtils.rightPad("bat", 5) = "bat " StringUtils.rightPad("bat", 1) = "bat" StringUtils.rightPad("bat", -1) = "bat"
str
- the String to pad out, may be nullsize
- the size to pad tonull
if null String inputpublic static String rightPad(String str, int size, char padChar)
Right pad a String with a specified character.
The String is padded to the size of size
.
StringUtils.rightPad(null, *, *) = null StringUtils.rightPad("", 3, 'z') = "zzz" StringUtils.rightPad("bat", 3, 'z') = "bat" StringUtils.rightPad("bat", 5, 'z') = "batzz" StringUtils.rightPad("bat", 1, 'z') = "bat" StringUtils.rightPad("bat", -1, 'z') = "bat"
str
- the String to pad out, may be nullsize
- the size to pad topadChar
- the character to pad withnull
if null String inputpublic static String rightPad(String str, int size, String padStr)
Right pad a String with a specified String.
The String is padded to the size of size
.
StringUtils.rightPad(null, *, *) = null StringUtils.rightPad("", 3, "z") = "zzz" StringUtils.rightPad("bat", 3, "yz") = "bat" StringUtils.rightPad("bat", 5, "yz") = "batyz" StringUtils.rightPad("bat", 8, "yz") = "batyzyzy" StringUtils.rightPad("bat", 1, "yz") = "bat" StringUtils.rightPad("bat", -1, "yz") = "bat" StringUtils.rightPad("bat", 5, null) = "bat " StringUtils.rightPad("bat", 5, "") = "bat "
str
- the String to pad out, may be nullsize
- the size to pad topadStr
- the String to pad with, null or empty treated as single spacenull
if null String inputpublic static String leftPad(String str, int size)
Left pad a String with spaces (' ').
The String is padded to the size of size
.
StringUtils.leftPad(null, *) = null StringUtils.leftPad("", 3) = " " StringUtils.leftPad("bat", 3) = "bat" StringUtils.leftPad("bat", 5) = " bat" StringUtils.leftPad("bat", 1) = "bat" StringUtils.leftPad("bat", -1) = "bat"
str
- the String to pad out, may be nullsize
- the size to pad tonull
if null String inputpublic static String leftPad(String str, int size, char padChar)
Left pad a String with a specified character.
Pad to a size of size
.
StringUtils.leftPad(null, *, *) = null StringUtils.leftPad("", 3, 'z') = "zzz" StringUtils.leftPad("bat", 3, 'z') = "bat" StringUtils.leftPad("bat", 5, 'z') = "zzbat" StringUtils.leftPad("bat", 1, 'z') = "bat" StringUtils.leftPad("bat", -1, 'z') = "bat"
str
- the String to pad out, may be nullsize
- the size to pad topadChar
- the character to pad withnull
if null String inputpublic static String leftPad(String str, int size, String padStr)
Left pad a String with a specified String.
Pad to a size of size
.
StringUtils.leftPad(null, *, *) = null StringUtils.leftPad("", 3, "z") = "zzz" StringUtils.leftPad("bat", 3, "yz") = "bat" StringUtils.leftPad("bat", 5, "yz") = "yzbat" StringUtils.leftPad("bat", 8, "yz") = "yzyzybat" StringUtils.leftPad("bat", 1, "yz") = "bat" StringUtils.leftPad("bat", -1, "yz") = "bat" StringUtils.leftPad("bat", 5, null) = " bat" StringUtils.leftPad("bat", 5, "") = " bat"
str
- the String to pad out, may be nullsize
- the size to pad topadStr
- the String to pad with, null or empty treated as single spacenull
if null String inputpublic static String abbreviate(String str, int maxWidth)
Abbreviates a String using ellipses. This will turn "Now is the time for all good men" into "Now is the time for..."
Specifically:
str
is less than maxWidth
characters
long, return it.(substring(str, 0, max-3) + "...")
.maxWidth
is less than 4
, throw an
IllegalArgumentException
.maxWidth
.StringUtils.abbreviate(null, *) = null StringUtils.abbreviate("", 4) = "" StringUtils.abbreviate("abcdefg", 6) = "abc..." StringUtils.abbreviate("abcdefg", 7) = "abcdefg" StringUtils.abbreviate("abcdefg", 8) = "abcdefg" StringUtils.abbreviate("abcdefg", 4) = "a..." StringUtils.abbreviate("abcdefg", 3) = IllegalArgumentException
str
- the String to check, may be nullmaxWidth
- maximum length of result String, must be at least 4null
if null String inputIllegalArgumentException
- if the width is too smallpublic static String abbreviate(String str, int offset, int maxWidth)
Abbreviates a String using ellipses. This will turn "Now is the time for all good men" into "...is the time for..."
Works like abbreviate(String, int)
, but allows you to specify
a "left edge" offset. Note that this left edge is not necessarily going to
be the leftmost character in the result, or the first character following the
ellipses, but it will appear somewhere in the result.
In no case will it return a String of length greater than
maxWidth
.
StringUtils.abbreviate(null, *, *) = null StringUtils.abbreviate("", 0, 4) = "" StringUtils.abbreviate("abcdefghijklmno", -1, 10) = "abcdefg..." StringUtils.abbreviate("abcdefghijklmno", 0, 10) = "abcdefg..." StringUtils.abbreviate("abcdefghijklmno", 1, 10) = "abcdefg..." StringUtils.abbreviate("abcdefghijklmno", 4, 10) = "abcdefg..." StringUtils.abbreviate("abcdefghijklmno", 5, 10) = "...fghi..." StringUtils.abbreviate("abcdefghijklmno", 6, 10) = "...ghij..." StringUtils.abbreviate("abcdefghijklmno", 8, 10) = "...ijklmno" StringUtils.abbreviate("abcdefghijklmno", 10, 10) = "...ijklmno" StringUtils.abbreviate("abcdefghijklmno", 12, 10) = "...ijklmno" StringUtils.abbreviate("abcdefghij", 0, 3) = IllegalArgumentException StringUtils.abbreviate("abcdefghij", 5, 6) = IllegalArgumentException
str
- the String to check, may be nulloffset
- left edge of source StringmaxWidth
- maximum length of result String, must be at least 4null
if null String inputIllegalArgumentException
- if the width is too smallpublic static boolean containsAny(String str, char... searchChars)
Checks if the String contains any character in the given set of characters.
A null
String will return false
.
A null
or zero length search array will return false
.
StringUtils.containsAny(null, *) = false StringUtils.containsAny("", *) = false StringUtils.containsAny(*, null) = false StringUtils.containsAny(*, []) = false StringUtils.containsAny("zzabyycdxx",['z','a']) = true StringUtils.containsAny("zzabyycdxx",['b','y']) = true StringUtils.containsAny("aba", ['z']) = false
str
- the String to check, may be nullsearchChars
- the chars to search for, may be nulltrue
if any of the chars are found,
false
if no match or null inputpublic static String replace(String text, String searchString, String replacement)
Replaces all occurrences of a String within another String.
A null
reference passed to this method is a no-op.
StringUtils.replace(null, *, *) = null StringUtils.replace("", *, *) = "" StringUtils.replace("any", null, *) = "any" StringUtils.replace("any", *, null) = "any" StringUtils.replace("any", "", *) = "any" StringUtils.replace("aba", "a", null) = "aba" StringUtils.replace("aba", "a", "") = "b" StringUtils.replace("aba", "a", "z") = "zbz"
text
- text to search and replace in, may be nullsearchString
- the String to search for, may be nullreplacement
- the String to replace it with, may be nullnull
if null String inputreplace(String text, String searchString, String replacement, int max)
public static String replace(String text, String searchString, String replacement, int max)
Replaces a String with another String inside a larger String,
for the first max
values of the search String.
A null
reference passed to this method is a no-op.
StringUtils.replace(null, *, *, *) = null StringUtils.replace("", *, *, *) = "" StringUtils.replace("any", null, *, *) = "any" StringUtils.replace("any", *, null, *) = "any" StringUtils.replace("any", "", *, *) = "any" StringUtils.replace("any", *, *, 0) = "any" StringUtils.replace("abaa", "a", null, -1) = "abaa" StringUtils.replace("abaa", "a", "", -1) = "b" StringUtils.replace("abaa", "a", "z", 0) = "abaa" StringUtils.replace("abaa", "a", "z", 1) = "zbaa" StringUtils.replace("abaa", "a", "z", 2) = "zbza" StringUtils.replace("abaa", "a", "z", -1) = "zbzz"
text
- text to search and replace in, may be nullsearchString
- the String to search for, may be nullreplacement
- the String to replace it with, may be nullmax
- maximum number of values to replace, or -1
if no maximumnull
if null String inputpublic static String replaceEach(String text, String[] searchList, String[] replacementList)
Replaces all occurrences of Strings within another String.
A null
reference passed to this method is a no-op, or if
any "search string" or "string to replace" is null, that replace will be
ignored. This will not repeat. For repeating replaces, call the
overloaded method.
StringUtils.replaceEach(null, *, *) = null StringUtils.replaceEach("", *, *) = "" StringUtils.replaceEach("aba", null, null) = "aba" StringUtils.replaceEach("aba", new String[0], null) = "aba" StringUtils.replaceEach("aba", null, new String[0]) = "aba" StringUtils.replaceEach("aba", new String[]{"a"}, null) = "aba" StringUtils.replaceEach("aba", new String[]{"a"}, new String[]{""}) = "b" StringUtils.replaceEach("aba", new String[]{null}, new String[]{"a"}) = "aba" StringUtils.replaceEach("abcde", new String[]{"ab", "d"}, new String[]{"w", "t"}) = "wcte" (example of how it does not repeat) StringUtils.replaceEach("abcde", new String[]{"ab", "d"}, new String[]{"d", "t"}) = "dcte"
text
- text to search and replace in, no-op if nullsearchList
- the Strings to search for, no-op if nullreplacementList
- the Strings to replace them with, no-op if nullnull
if
null String inputIndexOutOfBoundsException
- if the lengths of the arrays are not the same (null is ok,
and/or size 0)public static <T> String join(T... elements)
Joins the elements of the provided array into a single String containing the provided list of elements.
No separator is added to the joined String. Null objects or empty strings within the array are represented by empty strings.
StringUtils.join(null) = null StringUtils.join([]) = "" StringUtils.join([null]) = "" StringUtils.join(["a", "b", "c"]) = "abc" StringUtils.join([null, "", "a"]) = "a"
T
- the specific type of values to join togetherelements
- the values to join together, may be nullnull
if null array inputpublic static String join(Object[] array, char separator)
Joins the elements of the provided array into a single String containing the provided list of elements.
No delimiter is added before or after the list. Null objects or empty strings within the array are represented by empty strings.
StringUtils.join(null, *) = null StringUtils.join([], *) = "" StringUtils.join([null], *) = "" StringUtils.join(["a", "b", "c"], ';') = "a;b;c" StringUtils.join(["a", "b", "c"], null) = "abc" StringUtils.join([null, "", "a"], ';') = ";;a"
array
- the array of values to join together, may be nullseparator
- the separator character to usenull
if null array inputpublic static String join(Object[] array, char separator, int startIndex, int endIndex)
Joins the elements of the provided array into a single String containing the provided list of elements.
No delimiter is added before or after the list. Null objects or empty strings within the array are represented by empty strings.
StringUtils.join(null, *) = null StringUtils.join([], *) = "" StringUtils.join([null], *) = "" StringUtils.join(["a", "b", "c"], ';') = "a;b;c" StringUtils.join(["a", "b", "c"], null) = "abc" StringUtils.join([null, "", "a"], ';') = ";;a"
array
- the array of values to join together, may be nullseparator
- the separator character to usestartIndex
- the first index to start joining from. It is
an error to pass in an end index past the end of the arrayendIndex
- the index to stop joining from (exclusive). It is
an error to pass in an end index past the end of the arraynull
if null array inputpublic static String join(Object[] array, String separator)
Joins the elements of the provided array into a single String containing the provided list of elements.
No delimiter is added before or after the list.
A null
separator is the same as an empty String ("").
Null objects or empty strings within the array are represented by
empty strings.
StringUtils.join(null, *) = null StringUtils.join([], *) = "" StringUtils.join([null], *) = "" StringUtils.join(["a", "b", "c"], "--") = "a--b--c" StringUtils.join(["a", "b", "c"], null) = "abc" StringUtils.join(["a", "b", "c"], "") = "abc" StringUtils.join([null, "", "a"], ',') = ",,a"
array
- the array of values to join together, may be nullseparator
- the separator character to use, null treated as ""null
if null array inputpublic static String join(Object[] array, String separator, int startIndex, int endIndex)
Joins the elements of the provided array into a single String containing the provided list of elements.
No delimiter is added before or after the list.
A null
separator is the same as an empty String ("").
Null objects or empty strings within the array are represented by
empty strings.
StringUtils.join(null, *) = null StringUtils.join([], *) = "" StringUtils.join([null], *) = "" StringUtils.join(["a", "b", "c"], "--") = "a--b--c" StringUtils.join(["a", "b", "c"], null) = "abc" StringUtils.join(["a", "b", "c"], "") = "abc" StringUtils.join([null, "", "a"], ',') = ",,a"
array
- the array of values to join together, may be nullseparator
- the separator character to use, null treated as ""startIndex
- the first index to start joining from. It is
an error to pass in an end index past the end of the arrayendIndex
- the index to stop joining from (exclusive). It is
an error to pass in an end index past the end of the arraynull
if null array inputpublic static boolean equals(Object object1, Object object2)
Compares two objects for equality, where either one or both
objects may be null
.
ObjectUtils.equals(null, null) = true ObjectUtils.equals(null, "") = false ObjectUtils.equals("", null) = false ObjectUtils.equals("", "") = true ObjectUtils.equals(Boolean.TRUE, null) = false ObjectUtils.equals(Boolean.TRUE, "true") = false ObjectUtils.equals(Boolean.TRUE, Boolean.TRUE) = true ObjectUtils.equals(Boolean.TRUE, Boolean.FALSE) = false
object1
- the first object, may be null
object2
- the second object, may be null
true
if the values of both objects are the samepublic static <T> T defaultIfNull(T object, T defaultValue)
Returns a default value if the object passed is null
.
ObjectUtils.defaultIfNull(null, null) = null ObjectUtils.defaultIfNull(null, "") = "" ObjectUtils.defaultIfNull(null, "zz") = "zz" ObjectUtils.defaultIfNull("abc", *) = "abc" ObjectUtils.defaultIfNull(Boolean.TRUE, *) = Boolean.TRUE
T
- the type of the objectobject
- the Object
to test, may be null
defaultValue
- the default value to return, may be null
object
if it is not null
, defaultValue otherwisepublic static String toCamelCaseLC(String string)
public static String[] split(String regex, CharSequence input)
Pattern.split(CharSequence, int)
.
This is useful if the matched split-tokens should be returned as well.
For example:
split("e", "hello world") // ["h", "e", "llo world"]
split("o", "hello world") // ["hell", "o", " w", "o", "rld"]
split("[eo]", "hello world") // ["h", "e", "ll", "o", " w", "o", "rld"]
The result will always be an odd-length array.
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