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

   toString ( )
   consume ( )
   toByteArray ( )
   consumeQuietly ( )
   getContentCharSet ( )

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

    format ( )
    parse ( )

11. org.apache.commons.codec.digest.DigestUtils

    md5Hex ( )
    shaHex ( )
    sha256Hex ( )
    sha1Hex ( )
    sha ( )
    md5 ( )
    sha512Hex ( )
    sha1 ( )

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 ( )

16. org.apache.commons.beanutils.BeanUtils

    copyProperties ( )
    getProperty ( )
    setProperty ( )
    describe ( )
    populate ( )
    copyProperty ( )
    cloneBean ( )

原文出处：http://www.programcreek.com/2015/12/top-10-java-utility-classes/

译文出处：http://www.programcreek.com/2015/12/top-10-java-utility-classes/