JAVA 常用工具种(转)

JAVA 常用工具类(转)
StringUtils

这是象面包和奶油一样必须的通用语言库，这个实用工具类包括一些很早以前在String中未包含的重要方法。

StringUtils.isEmpty(null) && StringUtils.isEmpty(""); // true    StringUtils.isBlank("   \n\t");                       // true    StringUtils.substringAfterLast("foo.bar.baz", ".");   // "baz"    StringUtils.substringBeforeLast("foo.bar.baz", ".");  // "foo.bar"    StringUtils.split("foo.bar.baz", '.');                // { "foo", "bar", "baz" }    StringUtils.split("foo,  bar,baz", ", ");             // { "foo", "bar", "baz" }    StringUtils.leftPad("1", 3, '0');                     // "001"    

IOUtils and FileUtils

在一种当你需要手动操作多个文件罕见情况下必须具备的工具，这两个工具很相似(FileUtils操作文件，IOUtils操作InputStream和Reader classes)，和捆绑常用IO.

File file1;  File file2;  InputStream inputStream;  OutputStream outputStream;    // copy one file into another  FileUtils.copyFile(file1, file2);  IOUtils.copy(inputStream, outputStream);    // read a file into a String  String s1 = FileUtils.readFileToString(file1);  String s2 = IOUtils.toString(inputStream);    // read a file into a list of Strings, one item per line  List<String> l1 = FileUtils.readLines(file1);  List<String> l2 = IOUtils.readLines(inputStream);    // put this in your finally() clause after manipulating streams  IOUtils.closeQuietly(inputStream);    // return the list of xml and text files in the specified folder and any subfolders  Collection<File> c1 = FileUtils.listFiles(file1, { "xml", "txt" }, true);    // copy one folder and its contents into another  FileUtils.copyDirectoryToDirectory(file1, file2);    // delete one folder and its contents  FileUtils.deleteDirectory(file1);  

Google collections

这是我所知道的最好的扩展实现包，其中一些被社区叫嚣着要加入JDK：

// create an ArrayList with three arguments  List<String> list = Lists.newArrayList("foo", "bar", "baz");    // notice that there is no generics or class cast,  // and still this line does not generate a warning.  Set<String> s = Sets.newConcurrentHashSet();    // intersect and union are basic features of a Set, if you ask me  Set<String> s = Sets.intersect(s1, s2);    // Example  of multiple values in a Map  ListMultimap<String, Validator> validators = new ArrayListMultimap<String, Validator>();  validators.put("save", new RequiredValidator());  validators.put("save", new StringValidator());  validators.put("delete", new NumberValidator());    validators.get("save"); // { RequiredValidator, StringValidator }  validators.get("foo");  // empty List (not null)  validators.values();    // { RequiredValidator, StringValidator, NumberValidator }  

java.util.concurrent

不是每个人都需要这么重的java.util.concurrent，但是很好用:

// a map that may be modified (by the same or different thread) while being iterated  Map<String, Something> repository = new ConcurrentHashMap<String, Something>();    // same with lists. This one is only available with Java 6  List<Something> list = new CopyOnWriteArrayList<Something>();  

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