StringUtils、IOUtils and FileUtils及一些好工具

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>();