Java Farms: JAVA Strings Utility methods

import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;

/**
* A set of commonly used utilities for {@link String}s
* */
public class Strings {

 /**
 * A function that encodes any Object string value i.e.
 * {@code String.valueOf(object)}, within single-quotes (')
 */
 public static final Function<Object, String> WITHIN_SINGLE_QUOTES = new WithinSingleQuoteFunction();
 private static final Function<Object, String> TO_STRING_FUNCTION = new ToStringFunction();

 /**
 * Returns {@code true} if the string is {@code null} or is an empty string. 
 * 
 * NOTE: Does not consider any whitespace characters in the string as
 * empty. If you want to consider whitespace characters as effectively empty
 * then use {@link Strings#isNullOrBlank(String)} instead.
 *
 * 
 * 
 * Example: {@code Strings.isNullOrEmpty(null)} or
 * {@code Strings.isNullOrEmpty("")} will return true
 *
 * @param inputString
 * string reference to check
 * @return {@code true} if the string is null or is an empty string
 */
 public static boolean isNullOrEmpty(String inputString) {
 return inputString == null || inputString.length() == 0;
 }

 /**
 * Returns {@code true} if the optional string is absent or is an
 * empty string. 
 * 
 * NOTE: Does not consider any whitespace characters in the string as
 * empty. If you want to consider whitespace characters as effectively empty
 * then use {@link Strings#isAbsentOrBlank(String)} instead.
 *
 * 
 * 
 * Example: {@code Strings.isAbsentOrEmpty(Optional.absent())} or
 * {@code Strings.isNullOrEmpty(Optional.of("")} will return true
 *
 * @param a
 * non-null optional inputString string reference to check
 * @return {@code true} if the optional string is absent or is an empty
 * string
 */
 public static boolean isAbsentOrEmpty(Optional<String> optionalInputString) {
 return optionalInputString.isPresent() == false
 || optionalInputString.get().length() == 0;
 }

 /**
 * Returns {@code true} if the string is {@code null} or is a blank string.
 * Considers any whitespace characters as blank. Trims the string to check
 * for blankness.
 *
 * 
 * 
 * NOTE: Does consider any whitespace characters in the string as
 * empty. If you do not want to consider whitespace characters as
 * effectively empty then use {@link Strings#isNullOrEmpty(String)} instead.
 *
 * 
 * 
 * Example: {@code Strings.isNullOrBlank(null)} or
 * {@code Strings.isNullOrBlank(" ")} will return true
 *
 * @param inputString
 * string reference to check
 * @return {@code true} if the string is null or is a blank string
 * (considering space, \t or other whitespace characters as blank)
 */
 public static boolean isNullOrBlank(String inputString) {
 return inputString == null || inputString.trim().length() == 0;
 }

 /**
 * Returns {@code true} if the optional string is absent or is a
 * blank string. Considers any whitespace characters as blank. Trims the
 * string to check for blankness.
 *
 * 
 * 
 * NOTE: Does consider any whitespace characters in the string as
 * empty. If you do not want to consider whitespace characters as
 * effectively empty then use {@link Strings#isAbsentOrEmpty(String)}
 * instead.
 *
 * 
 * 
 * Example: {@code Strings.isAbsentOrBlank(Optinal.absent())} or
 * {@code Strings.isAbsentOrBlank(Optional.of(" ")} will return true
 *
 * @param a
 * non-null optional inputString string reference to check
 * @return {@code true} if the optional string is absent or is a blank
 * string (considering space, \t or other whitespace characters as
 * blank)
 * @throws NullPointerException
 * if inputString is null
 */
 public static boolean isAbsentOrBlank(Optional<String> optionalInputString) {
 return optionalInputString.isPresent() == false
 || optionalInputString.get().trim().length() == 0;
 }

 /**
 * Returns a string consisting of a specific number of concatenated copies
 * of an input string. For example, {@code repeat("hey", 3)} returns the
 * string {@code "heyheyhey"}.
 *
 * @param string
 * any non-null string
 * @param count
 * the number of times to repeat it; a nonnegative integer
 * @return a string containing {@code string} repeated {@code count} times
 * (the empty string if {@code count} is zero)
 * @throws IllegalArgumentException
 * if {@code count} is negative
 */
 public static String repeat(String string, int count) {
 checkNotNull(string, "string is null");

 if (count <= 1) {
 checkArgument(count >= 0, "invalid count: " + count);
 return (count == 0) ? "" : string;
 }

 final int len = string.length();
 final long longSize = (long) len * (long) count;
 final int size = (int) longSize;
 if (size != longSize) {
 throw new ArrayIndexOutOfBoundsException(
 "Required array size too large: " + longSize);
 }

 final char[] array = new char[size];
 string.getChars(0, len, array, 0);
 int n;
 for (n = len; n < size - n; n <<= 1) {
 System.arraycopy(array, 0, array, n, n);
 }
 System.arraycopy(array, 0, array, n, size - n);
 return new String(array);
 }

 /**
 * Joins the String representation ( {@code String.valueOf(..)} ) of each
 * part given in {@code parts} array using the separator provided.
 *
 * 
 * Example: <code>
 * Strings.join(",", new String[]{"a","b"})
 * }</code> will return {@code a,b}
 * 
 * NOTE: This method skips any {@code null} parts encountered.
 *
 * 
 * Example: {@code Strings.join(",", new String[] "a",null,"b"})} will
 * return {@code a,b}
 *
 * @param separator
 * any non-null string
 * @param parts
 * are the objects whose string representation will be joined
 * using separator
 * @return a string containing the string representation of each part with
 * separator in between each
 */
 public static String join(String separator, Object[] parts) {
 return join(separator, parts, TO_STRING_FUNCTION);
 }

 /**
 * Joins the String representation of each part in {@code parts} by applying
 * {@code partFunction} on it, using the separator provided.
 *
 * 
 * Example: <code>
 * Strings.join(",", new String[]{"a","b"}, Strings.WITHIN_SINGLE_QUOTES)
 * }</code> will return {@code 'a','b'}
 * 
 * NOTE: This method skips any {@code null} parts encountered.
 *
 * 
 * Example: {@code Strings.join(",", new String[] "a",null,"b"},
 * Strings.WITHIN_SINGLE_QUOTES)} will return {@code 'a','b'}
 *
 * @param separator
 * any non-null string
 * @param parts
 * are the objects whose string representation will be joined
 * using separator
 * @param partFunction
 * a non-null function that will be applied to all non-null parts
 * @return a string containing the string representation of each part with
 * separator in between each
 */
 public static String join(String separator, Object[] parts,
 Function<Object, String> partFunction) {
 checkNotNull(parts, "parts are null");
 return join(separator, Arrays.asList(parts), partFunction);
 }

 /**
 * @see Strings#join(String, Object[])
 */
 public static String join(String string, Iterable<?> parts) {
 return join(string, parts, TO_STRING_FUNCTION);
 }

 /**
 * @see Strings#join(String, Object[], Function)
 */
 public static String join(String string, Iterable<?> parts,
 Function<Object, String> partFunction) {
 checkNotNull(parts, "parts are null");
 return join(string, parts.iterator(), partFunction);
 }

 private static String join(String separator, Iterator<?> parts,
 Function<Object, String> partFunction) {
 checkNotNull(separator, "separator is null");
 checkNotNull(partFunction, "partFunction is null");

 StringBuilder builder = new StringBuilder();

 while (parts.hasNext()) {
 Object part = parts.next();
 if (part != null) {
 builder.append(partFunction.apply(part));
 break;
 }
 }

 while (parts.hasNext()) {
 Object part = parts.next();
 if (part != null) {
 builder.append(separator);
 builder.append(partFunction.apply(part));
 }
 }
 return builder.toString();
 }

 /**
 * Returns a string, of length at least {@code minLength}, consisting of
 * {@code string} prepended with as many copies of {@code padChar} as are
 * necessary to reach that length. For example,
 *
 * <ul>
 * <li>{@code padStart("7", 3, '0')} returns {@code "007"}
 * <li>{@code padStart("2010", 3, '0')} returns {@code "2010"}
 * </ul>
 *
 * @param string
 * the string which should appear at the end of the result
 * @param minLength
 * the minimum length the resulting string must have. Can be zero
 * or negative, in which case the input string is always
 * returned.
 * @param padChar
 * the character to insert at the beginning of the result until
 * the minimum length is reached
 * @return the padded string
 */
 public static String padStart(String string, int minLength, char padChar) {
 checkNotNull(string, "string is null");
 if (string.length() >= minLength) {
 return string;
 }

 int padCount = minLength - string.length();
 StringBuilder builder = new StringBuilder(minLength);
 for (int i = 0; i < padCount; i++) {
 builder.append(padChar);
 }

 builder.append(string);
 return builder.toString();
 }

 /**
 * Returns a string, of length at least {@code minLength}, consisting of
 * {@code string} appended with as many copies of {@code padChar} as are
 * necessary to reach that length. For example,
 *
 * <ul>
 * <li>{@code padEnd("4.", 5, '0')} returns {@code "4.000"}
 * <li>{@code padEnd("2010", 3, '!')} returns {@code "2010"}
 * </ul>
 *
 * @param string
 * the string which should appear at the beginning of the result
 * @param minLength
 * the minimum length the resulting string must have. Can be zero
 * or negative, in which case the input string is always
 * returned.
 * @param padChar
 * the character to append to the end of the result until the
 * minimum length is reached
 * @return the padded string
 */
 public static String padEnd(String string, int minLength, char padChar) {
 checkNotNull(string, "string is null");
 if (string.length() >= minLength) {
 return string;
 }

 int padCount = minLength - string.length();
 StringBuilder builder = new StringBuilder(minLength);
 builder.append(string);
 for (int i = 0; i < padCount; i++) {
 builder.append(padChar);
 }

 return builder.toString();
 }

 static class WithinSingleQuoteFunction implements Function<Object, String> {

 private static final String SINGLE_QUOTE = "'";

 @Override
 public String apply(Object input) {
 return SINGLE_QUOTE + TO_STRING_FUNCTION.apply(input)
 + SINGLE_QUOTE;
 }
 }

 static class ToStringFunction implements Function<Object, String> {

 @Override
 public String apply(Object input) {
 return String.valueOf(input);
 }
 }

 /**
 * Provides a splitter for given separator.
 *
 * @param separator
 * on which split is done.
 *
 * @return Splitter on Separator.
 * @see Splitter
 */
 public static Splitter splitter(final char separator) {
 return Splitter.on(separator);
 }

 /**
 * Returns predicate which evaluates to true if the string passed is
 * non-null and non-empty. It can be used in other utilities such as
 * {@link Collectionz#filter(java.util.Collection, Predicate)}
 *
 * 
 * Usage:
 *
 * <pre>
 * <code>Collectionz.filter(unfilteredCollection, Strings.nonNullAndNonEmpty())
 * </code>
 * </pre>
 *
 * @return predicate which evaluates to true if the string passed is
 * non-null and non-empty
 * @see Predicate
 * @see Collectionz
 */
 public static Predicate<String> nonNullAndNonEmpty() {
 return NonNullAndNonEmpty.INSTANCE;
 }

 private static enum NonNullAndNonEmpty implements Predicate<String> {
 INSTANCE;

 @Override
 public boolean apply(String input) {
 return isNullOrEmpty(input) == false;
 }
 }

 /**
 * Returns predicate which evaluates to true if the string passed is
 * non-null and non-blank (whitespace characters are considered as empty).
 * It can be used in other utilities such as
 * {@link Collectionz#filter(java.util.Collection, Predicate)}
 *
 * 
 * Usage:
 *
 * <pre>
 * <code>Collectionz.filter(unfilteredCollection, Strings.nonNullAndNonBlank())
 * </code>
 * </pre>
 *
 * @return predicate which evaluates to true if the string passed is
 * non-null and non-blank
 * @see Predicate
 * @see Collectionz
 */
 public static Predicate<String> nonNullAndNonBlank() {
 return NonNullAndNonBlank.INSTANCE;
 }

 private static enum NonNullAndNonBlank implements Predicate<String> {
 INSTANCE;

 @Override
 public boolean apply(String input) {
 return isNullOrBlank(input) == false;
 }
 }

 /**
 * Filters all null or empty elements from the underlying {@code collection}
 *
 * 
 * NOTE: Does not remove blank elements, use
 * {@link Strings#filterNullOrBlank(Collection)} for that.
 *
 * 
 * It has the same effect as calling
 * {@code Collectionz.filter(collection, Strings.nonNullAndNonEmpty());}
 *
 * @param collection
 * a non-null collection of strings
 * @throws NullPointerException
 * if collection passed is null
 */
 public static void filterNullOrEmpty(Collection<String> collection) {
 Collectionz.filter(collection, nonNullAndNonEmpty());
 }

 /**
 * Filters all null or blank elements from the underlying {@code collection}
 * , elements containing just whitespace characters are also removed from
 * the collection.
 *
 * 
 * NOTE: For removing just empty elements, use
 * {@link Strings#filterNullOrEmpty(Collection)} for that.
 *
 * 
 * It has the same effect as calling
 * {@code Collectionz.filter(collection, Strings.nonNullAndNonBlank());}
 *
 * @param collection
 * a non-null collection of strings
 * @throws NullPointerException
 * if collection passed is null
 */
 public static void filterNullOrBlank(Collection<String> collection) {
 Collectionz.filter(collection, nonNullAndNonBlank());
 }

 /**
 * Returns {@code true} if trimmed input is true or yes, false otherwise.
 * 
 * Note that this method trims the input and performs a case insensitive match.
 */
 public static boolean toBoolean(String booleanInString) {
 if (booleanInString == null) {
 return false;
 }

 String trimmedString = booleanInString.trim();
 return "true".equalsIgnoreCase(trimmedString)
 || "yes".equalsIgnoreCase(trimmedString);
 }

 /**
 * Returns a function that converts the string to integer.
 * 
 * Note that the returned function throws {@code NumberFormatException} if the
 * string does not contain a parsable integer.
 *
 * @see Integer#parseInt(String)
 */
 public static Function<String, Integer> toInt() {
 return ToIntFunction.INSTANCE;
 }

 private static enum ToIntFunction implements Function<String, Integer> {
 INSTANCE;

 @Override
 public Integer apply(String input) {
 return Integer.parseInt(input);
 }
 }
}

/**
* Simple static methods to be called at the start of your own methods to verify
* correct arguments and state. This allows constructs such as
* <pre>
* if (count <= 0) {
* throw new IllegalArgumentException("must be positive: " + count);
* }</pre>
*
* to be replaced with the more compact
* <pre>
* checkArgument(count > 0, "must be positive: %s", count);
* </pre>
*
* Use of check nulls can be used before assigning the references for fail fast approach such as
* <pre>
* class MyClass{
* public MyClass(Object arg1, Object arg2){
* this.arg1 = checkNotNull(arg1,"arg1 is null");
* this.arg2 = checkNotNull(arg2,"arg2 is null");
* }
* }</pre>
*
* NOTE: Best when used as static imports.
*
*
*
*/
public class Preconditions {
 private Preconditions(){}

 /**
 * Ensures that an object reference passed as a parameter to the calling method is not null.
 *
 * @param reference an object reference
 * @param errorMessage the exception message to use if the check fails; will be converted to a
 * string using {@link String#valueOf(Object)}
 * @return the non-null reference that was validated
 * @throws NullPointerException if {@code reference} is null
 */
 public static <T> T checkNotNull(T reference, Object errorMessage) {
 if (reference == null) {
 throw new NullPointerException(String.valueOf(errorMessage));
 }
 return reference;
 }

 /**
 * Ensures the truth of an expression involving one or more parameters to the calling method.
 *
 * @param expression a boolean expression
 * @param errorMessage the exception message to use if the check fails; will be converted to a
 * string using {@link String#valueOf(Object)}
 * @throws IllegalArgumentException if {@code expression} is false
 */
 public static void checkArgument(boolean expression, Object errorMessage) {
 if (!expression) {
 throw new IllegalArgumentException(String.valueOf(errorMessage));
 }
 }

 /**
 * Ensures the truth of an expression involving the state of the calling instance, but not
 * involving any parameters to the calling method.
 *
 * @param expression a boolean expression
 * @param errorMessage the exception message to use if the check fails; will be converted to a
 * string using {@link String#valueOf(Object)}
 * @throws IllegalStateException if {@code expression} is false
 */
 public static void checkState(boolean expression, Object errorMessage) {
 if (!expression) {
 throw new IllegalStateException(String.valueOf(errorMessage));
 }
 }
}

Java Farms

Tuesday, September 8, 2015

JAVA Strings Utility methods

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