（转载： http://www.hollischuang.com/archives/1606）
github地址： https://github.com/liufeiSAP/javaStudy.git
在Java中，有很多比较实用的类库，他们通常都定义了一系列具有常见功能的方法。本文总结了最常用的Java中的实用类以及他们的最常用的方法。无论是类和类中方法都是按照流行程度来排序的。
本文中列出来的类及方法都是经过大量实践的常用类库及方法，我们可以直接拿过来用。当然，这些方法实现的功能我们自己都能实现，但是既然已经有很成熟的方法可以供我们使用了，那么就无需自己定义了。很多类和方法通过他们的名字其实可以理解出具体是做什么的。每个方法都有一个链接，可以查看他们在开源代码中具体是如何使用的。
以下列表是通过分析50K的开源项目得出来的。
1. org.apache.commons.io.IOUtils
- closeQuietly ( )
- toString ( )
- copy ( )
- toByteArray ( )
- write ( )
- toInputStream ( )
- readLines ( )
- copyLarge ( )
- lineIterator ( )
- readFully ( )
2. org.apache.commons.io.FileUtils
- deleteDirectory ( )
- readFileToString ( )
- deleteQuietly ( )
- copyFile ( )
- writeStringToFile ( )
- forceMkdir ( )
- write ( )
- listFiles ( )
- copyDirectory ( )
- forceDelete ( )
3. org.apache.commons.lang.StringUtils
- isBlank ( )
- isNotBlank ( )
- isEmpty ( )
- isNotEmpty ( )
- equals ( )
- join ( )
- split ( )
- EMPTY
- trimToNull ( )
- replace ( )
4. org.apache.http.util.EntityUtils
5. org.apache.commons.lang3.StringUtils
- isBlank ( )
- isNotBlank ( )
- isEmpty ( )
- isNotEmpty ( )
- join ( )
- equals ( )
- split ( )
- EMPTY
- replace ( )
- capitalize ( )
6. org.apache.commons.io.FilenameUtils
- getExtension ( )
- getBaseName ( )
- getName ( )
- concat ( )
- removeExtension ( )
- normalize ( )
- wildcardMatch ( )
- separatorsToUnix ( )
- getFullPath ( )
- isExtension ( )
7. org.springframework.util.StringUtils
- hasText ( )
- hasLength ( )
- isEmpty ( )
- commaDelimitedListToStringArray ( )
- collectionToDelimitedString ( )
- replace ( )
- delimitedListToStringArray ( )
- uncapitalize ( )
- collectionToCommaDelimitedString ( )
- tokenizeToStringArray ( )
8. org.apache.commons.lang.ArrayUtils
- contains ( )
- addAll ( )
- clone ( )
- isEmpty ( )
- add ( )
- EMPTY_BYTE_ARRAY
- subarray ( )
- indexOf ( )
- isEquals ( )
- toObject ( )
9. org.apache.commons.lang.StringEscapeUtils
- escapeHtml ( )
- unescapeHtml ( )
- escapeXml ( )
- escapeSql ( )
- unescapeJava ( )
- escapeJava ( )
- escapeJavaScript ( )
- unescapeXml ( )
- unescapeJavaScript ( )
10. org.apache.http.client.utils.URLEncodedUtils
11. org.apache.commons.codec.digest.DigestUtils
12. org.apache.commons.collections.CollectionUtils
- isEmpty ( )
- isNotEmpty ( )
- select ( )
- transform ( )
- filter ( )
- find ( )
- collect ( )
- forAllDo ( )
- addAll ( )
- isEqualCollection ( )
13. org.apache.commons.lang3.ArrayUtils
- contains ( )
- isEmpty ( )
- isNotEmpty ( )
- add ( )
- clone ( )
- addAll ( )
- subarray ( )
- indexOf ( )
- EMPTY_OBJECT_ARRAY
- EMPTY_STRING_ARRAY
14. org.apache.commons.beanutils.PropertyUtils
- getProperty ( )
- setProperty ( )
- getPropertyDescriptors ( )
- isReadable ( )
- copyProperties ( )
- getPropertyDescriptor ( )
- getSimpleProperty ( )
- isWriteable ( )
- setSimpleProperty ( )
- getPropertyType ( )
15. org.apache.commons.lang3.StringEscapeUtils
- unescapeHtml4 ( )
- escapeHtml4 ( )
- escapeXml ( )
- unescapeXml ( )
- escapeJava ( )
- escapeEcmaScript ( )
- unescapeJava ( )
- escapeJson ( )
- escapeXml10 ( )