Java常用工具类

StringUtils

叫StringUtils或StringUtil的实在是太多了，首先就是大名鼎鼎的org.apache.commons.lang3.StringUtils，提供了如isEmpty、isNotEmpty、isBlank、isNotBlank等等的常用字符串判空方法，非常的实用；另外一个比较常见的提供者就是org.springframework.util.StringUtils，我们在看Spring的源码的时候经常会见到，但其实他用的是自己写的工具类，并不是apache提供的，这里面也提供了许多类似的方法，如isEmpty、hasLength、hasText等，如果你的系统采用的是Spring框架的话，那么可以直接使用这个工具类。

BeanUtils

org.springframework.beans.BeanUtils
JavaBeans的静态方法：用于实例化bean、检查bean属性类型、复制bean属性等。

避免用Apache Beanutils进行属性的copy。
说明：Apache BeanUtils性能较差，可以使用其他方案比如Spring BeanUtils, Cglib BeanCopier
-- 阿里巴巴Java开发规范

public static void copyProperties(Object source, Object target) throws BeansException

StandardCharsets

java.nio.charset.StandardCharsets
如果不想直接写"UTF-8"这个字符串，那么可以直接用StandardCharsets.UTF_8.name()。
支持的Charset：

    /**
     * Seven-bit ASCII, a.k.a. ISO646-US, a.k.a. the Basic Latin block of the
     * Unicode character set
     */
    public static final Charset US_ASCII = Charset.forName("US-ASCII");
    /**
     * ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1
     */
    public static final Charset ISO_8859_1 = Charset.forName("ISO-8859-1");
    /**
     * Eight-bit UCS Transformation Format
     */
    public static final Charset UTF_8 = Charset.forName("UTF-8");
    /**
     * Sixteen-bit UCS Transformation Format, big-endian byte order
     */
    public static final Charset UTF_16BE = Charset.forName("UTF-16BE");
    /**
     * Sixteen-bit UCS Transformation Format, little-endian byte order
     */
    public static final Charset UTF_16LE = Charset.forName("UTF-16LE");
    /**
     * Sixteen-bit UCS Transformation Format, byte order identified by an
     * optional byte-order mark
     */
    public static final Charset UTF_16 = Charset.forName("UTF-16");

CharEncoding

org.apache.commons.lang3.CharEncoding
里面定义了许多常用的编码格式
如 ISO-8859-1、US-ASCII、UTF-8

/**
* @deprecated Please use {@link Charset#isSupported(String)} instead, although be aware that {@code null}
* values are not accepted by that method and an {@link IllegalCharsetNameException} may be thrown.
*/
boolean isSupported(final String name)

新版的CharEncoding已经被标记为@Deprecated，因为JDK7已经自带了java.nio.charset.StandardCharsets，我们可以直接使用JDK自带的StandardCharsets。

HtmlUtils

org.springframework.web.util.HtmlUtils

//对HTML里的标签进行转义
public static String htmlEscape(String input, String encoding)

另见org.springframework.web.util.JavaScriptUtils

ObjectUtils

org.springframework.util.ObjectUtils

// Determine whether the given object is empty
public static boolean isEmpty(@Nullable Object obj)
// Determine whether the given array is empty
public static boolean isEmpty(@Nullable Object[] array) {
// Return whether the given throwable is a checked exception
public static boolean isCheckedException(Throwable ex)
// Determine whether the given object is an array
public static boolean isArray(@Nullable Object obj)

FileUtils

org.apache.commons.io.FileUtils
文件复制，文件转换等（同org.springframework.util.FileCopyUtils）

public static void copyFile(final File srcFile, final File destFile)
public static void copyDirectoryToDirectory(final File srcDir, final File destDir)
public static void touch(final File file) throws IOException
public static void deleteDirectory(final File directory)
public static String readFileToString(final File file, final Charset encoding) throws IOException
public static void writeStringToFile(final File file, final String data, final Charset encoding,
                                         final boolean append) throws IOException
public static void moveFile(final File srcFile, final File destFile) throws IOException
// Returns the size of the specified file or directory.
public static long sizeOf(final File file)
// Deletes a file. If file is a directory, delete it and all sub-directories.
public static void forceDelete(final File file) throws IOException
// Determines whether the specified file is a Symbolic Link rather than an actual file.
public static boolean isSymlink(final File file) throws IOException

FilenameUtils

org.apache.commons.io.FilenameUtils
获取文件名、扩展名等

// 获取文件名，如a/b/c.txt --> c.txt
public static String getName(final String filename)
// 获取文件名的扩展名，如foo.txt      --> "txt"
//       a/b/c.jpg    --> "jpg"
//       a/b.txt/c    --> ""
//       a/b/c        --> ""
public static String getExtension(final String filename)
// 去除扩展名
public static String removeExtension(final String filename)

IOUtils

org.apache.commons.io.IOUtils
通用IO流操作实用工具。

public static String toString(final InputStream input, final Charset encoding)
public static void write(final String data, final OutputStream output, final Charset encoding) throws IOException

DigestUtils

org.springframework.util.DigestUtils
计算摘要的各种方法。推荐使用Apache Commons Codec用于更全面的摘要实用程序套件。