234 lines
10 KiB
Java
234 lines
10 KiB
Java
/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/**
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* <p>
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* Provides highly reusable static utility methods, chiefly concerned with
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* adding value to the {@link java.lang} classes. Most of these classes are
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* immutable and thus thread-safe. However
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* {@link org.apache.commons.lang3.CharSet} is not currently guaranteed
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* thread-safe under all circumstances.
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* </p>
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*
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* <p>
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* The top level package contains various Utils classes, whilst there are
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* various subpackages including {@link org.apache.commons.lang3.math},
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* {@link org.apache.commons.lang3.concurrent} and
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* {@link org.apache.commons.lang3.builder}. Using the Utils classes is
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* generally simplicity itself. They are the equivalent of global functions in
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* another language, a collection of stand-alone, thread-safe, static methods.
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* In contrast, subpackages may contain interfaces which may have to be
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* implemented or classes which may need to be extended to get the full
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* functionality from the code. They may, however, contain more global-like
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* functions.
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* </p>
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*
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* <p>
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* Lang 3.0 requires JDK 1.5+, since Lang 3.2 it requires JDK 6+; The legacy
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* release 2.6 requires JDK 1.2+. In both cases you can find features of later
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* JDKs being maintained by us and likely to be removed or modified in favour of
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* the JDK in the next major version. Note that Lang 3.0 uses a different
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* package than its predecessors, allowing it to be used at the same time as an
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* earlier version.
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* </p>
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*
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* <p>
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* You will find deprecated methods as you stroll through the Lang
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* documentation. These are removed in the next major version.
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* </p>
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*
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* <p>
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* All util classes contain empty public constructors with warnings not to use.
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* This may seem an odd thing to do, but it allows tools like Velocity to access
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* the class as if it were a bean. In other words, yes we know about private
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* constructors and have chosen not to use them.
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* </p>
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*
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* <h2>String manipulation - StringUtils, StringEscapeUtils,
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* RandomStringUtils</h2>
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*
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* <p>
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* Lang has a series of String utilities. The first is
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* {@link org.apache.commons.lang3.StringUtils}, oodles and oodles of functions
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* which tweak, transform, squeeze and cuddle {@link java.lang.String
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* java.lang.Strings}. In addition to StringUtils, there are a series of other
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* String manipulating classes;
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* {@link org.apache.commons.lang3.RandomStringUtils} and
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* {@link org.apache.commons.lang3.StringEscapeUtils StringEscapeUtils}.
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* RandomStringUtils speaks for itself. It's provides ways in which to generate
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* pieces of text, such as might be used for default passwords.
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* StringEscapeUtils contains methods to escape and unescape Java, JavaScript,
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* JSON, HTML and XML.
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* </p>
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*
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* <p>
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* These are ideal classes to start using if you're looking to get into Lang.
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* StringUtils' {@link org.apache.commons.lang3.StringUtils#capitalize(String)},
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* {@link org.apache.commons.lang3.StringUtils#substringBetween(String, String)}/{@link org.apache.commons.lang3.StringUtils#substringBefore(String, String)
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* Before}/{@link org.apache.commons.lang3.StringUtils#substringAfter(String, String)
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* After}, {@link org.apache.commons.lang3.StringUtils#split(String)} and
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* {@link org.apache.commons.lang3.StringUtils#join(Object[])} are good methods
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* to begin with.
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* </p>
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*
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* <h2>Character handling - CharSetUtils, CharSet, CharRange, CharUtils</h2>
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*
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* <p>
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* In addition to dealing with Strings, it's also important to deal with chars
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* and Characters. {@link org.apache.commons.lang3.CharUtils} exists for this
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* purpose, while {@link org.apache.commons.lang3.CharSetUtils} exists for
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* set-manipulation of Strings. Be careful, although CharSetUtils takes an
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* argument of type String, it is only as a set of characters. For example,
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* {@code CharSetUtils.delete("testtest", "tr")} will remove all t's and all r's
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* from the String, not just the String "tr".
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* </p>
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*
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* <p>
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* {@link org.apache.commons.lang3.CharRange} and
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* {@link org.apache.commons.lang3.CharSet} are both used internally by
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* CharSetUtils, and will probably rarely be used.
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* </p>
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*
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* <h2>JVM interaction - SystemUtils, CharEncoding</h2>
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*
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* <p>
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* SystemUtils is a simple little class which makes it easy to find out
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* information about which platform you are on. For some, this is a necessary
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* evil. It was never something I expected to use myself until I was trying to
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* ensure that Commons Lang itself compiled under JDK 1.2. Having pushed out a
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* few JDK 1.3 bits that had slipped in ({@code Collections.EMPTY_MAP} is a
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* classic offender), I then found that one of the Unit Tests was dying
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* mysteriously under JDK 1.2, but ran fine under JDK 1.3. There was no obvious
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* solution and I needed to move onwards, so the simple solution was to wrap
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* that particular test in a
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* <code>if (SystemUtils.isJavaVersionAtLeast(1.3f)) {</code>, make a note and
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* move on.
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* </p>
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*
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* <p>
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* The {@link org.apache.commons.lang3.CharEncoding} class is also used to
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* interact with the Java environment and may be used to see which character
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* encodings are supported in a particular environment.
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* </p>
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*
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* <h2>Serialization - SerializationUtils, SerializationException</h2>
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*
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* <p>
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* Serialization doesn't have to be that hard! A simple util class can take away
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* the pain, plus it provides a method to clone an object by unserializing and
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* reserializing, an old Java trick.
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* </p>
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*
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* <h3>Assorted functions - ObjectUtils, ClassUtils, ArrayUtils,
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* BooleanUtils</h3>
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*
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* <p>
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* Would you believe it, {@link org.apache.commons.lang3.ObjectUtils} contains
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* handy functions for Objects, mainly null-safe implementations of the methods
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* on {@link java.lang.Object}.
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* </p>
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*
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* <p>
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* {@link org.apache.commons.lang3.ClassUtils} is largely a set of helper
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* methods for reflection. Of special note are the comparators hidden away in
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* ClassUtils, useful for sorting Class and Package objects by name; however
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* they merely sort alphabetically and don't understand the common habit of
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* sorting {@code java} and {@code javax} first.
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* </p>
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*
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* <p>
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* Next up, {@link org.apache.commons.lang3.ArrayUtils}. This is a big one with
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* many methods and many overloads of these methods so it is probably worth an
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* in depth look here. Before we begin, assume that every method mentioned is
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* overloaded for all the primitives and for Object. Also, the short-hand 'xxx'
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* implies a generic primitive type, but usually also includes Object.
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* </p>
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*
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* <ul>
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* <li>ArrayUtils provides singleton empty arrays for all the basic types. These
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* will largely be of use in the Collections API with its toArray methods, but
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* also will be of use with methods which want to return an empty array on
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* error.</li>
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* <li>{@code add(xxx[], xxx)} will add a primitive type to an array, resizing
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* the array as you'd expect. Object is also supported.</li>
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* <li>{@code clone(xxx[])} clones a primitive or Object array.</li>
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* <li>{@code contains(xxx[], xxx)} searches for a primitive or Object in a
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* primitive or Object array.</li>
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* <li>{@code getLength(Object)} returns the length of any array or an
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* IllegalArgumentException if the parameter is not an array.
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* {@code hashCode(Object)}, {@code equals(Object, Object)},
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* {@code toString(Object)}</li>
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* <li>{@code indexOf(xxx[], xxx)} and {@code indexOf(xxx[], xxx, int)} are
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* copies of the classic String methods, but this time for primitive/Object
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* arrays. In addition, a lastIndexOf set of methods exists.</li>
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* <li>{@code isEmpty(xxx[])} lets you know if an array is zero-sized or null.
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* </li>
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* <li>{@code isSameLength(xxx[], xxx[])} returns true if the arrays are the
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* same length.</li>
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* <li>Along side the add methods, there are also remove methods of two types.
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* The first type remove the value at an index, {@code remove(xxx[], int)},
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* while the second type remove the first value from the array,
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* {@code remove(xxx[], xxx)}.</li>
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* <li>Nearing the end now. The {@code reverse(xxx[])} method turns an array
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* around.</li>
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* <li>The {@code subarray(xxx[], int, int)} method splices an array out of a
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* larger array.</li>
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* <li>Primitive to primitive wrapper conversion is handled by the
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* {@code toObject(xxx[])} and {@code toPrimitive(Xxx[])} methods.</li>
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* </ul>
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*
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* <p>
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* Lastly, {@link org.apache.commons.lang3.ArrayUtils#toMap(Object[])} is worthy
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* of special note. It is not a heavily overloaded method for working with
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* arrays, but a simple way to create Maps from literals.
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* </p>
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*
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* <h4>Using toMap</h4>
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*
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* <pre>
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* <code>
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* Map colorMap = ArrayUtils.toMap(new String[][] {{
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* {"RED", "#FF0000"},
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* {"GREEN", "#00FF00"},
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* {"BLUE", "#0000FF"}
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* });
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* </code>
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* </pre>
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*
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* <p>
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* Our final util class is {@link org.apache.commons.lang3.BooleanUtils}. It
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* contains various Boolean acting methods, probably of most interest is the
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* {@link org.apache.commons.lang3.BooleanUtils#toBoolean(String)} method which
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* turns various positive/negative Strings into a Boolean object, and not just
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* true/false as with Boolean.valueOf.
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* </p>
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*
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* <h2>Flotsam - BitField, Validate</h2>
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* <p>
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* On reaching the end of our package, we are left with a couple of classes that
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* haven't fit any of the topics so far.
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* </p>
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* <p>
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* The {@link org.apache.commons.lang3.BitField} class provides a wrapper class
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* around the classic bitmask integer, whilst the
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* {@link org.apache.commons.lang3.Validate} class may be used for assertions
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* (remember, we support Java 1.2).
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* </p>
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*
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* @since 1.0
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*/
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package org.apache.commons.lang3;
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