Java常用工具类

 

Ignacio Coloma 说道：作为一个软件开发者，缺乏想象力是最严重的罪过之一。我们经常把事情重复做一遍又一遍，但是我们很少改变这种方式，至少我是这样。经过这些年开发，在我的工具箱里面有了一些每个项目我都需要用到的工具，烦人的重复工作不再是我的事。

下面这些工具也许你已经用到，让我来仔细介绍它们：

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。

Java代码

1. StringUtils.isEmpty( null ) && StringUtils.isEmpty( "" ); // true
2. StringUtils.isBlank(" \n\t" ); // true
3. StringUtils.substringAfterLast("foo.bar.baz" , "." ); // "baz"
4. StringUtils.substringBeforeLast("foo.bar.baz" , "." ); // "foo.bar"
5. StringUtils.split("foo.bar.baz" , '.' ); // { "foo", "bar", "baz" }
6. StringUtils.split("foo, bar,baz" , ", " ); // { "foo", "bar", "baz" }
7. 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.

Java代码

1. File file1;
2. File file2;
3. InputStream inputStream;
4. OutputStream outputStream;
5. // copy one file into another
6. FileUtils.copyFile(file1, file2);
7. IOUtils.copy(inputStream, outputStream);
8. // read a file into a String
9. String s1 = FileUtils.readFileToString(file1);
10. String s2 = IOUtils.toString(inputStream);
11. // read a file into a list of Strings, one item per line
12. List<String> l1 = FileUtils.readLines(file1);
13. List<String> l2 = IOUtils.readLines(inputStream);
14. // put this in your finally() clause after manipulating streams
15. IOUtils.closeQuietly(inputStream);
16. // return the list of xml and text files in the specified folder and any subfolders
17. Collection<File> c1 = FileUtils.listFiles(file1, { "xml" , "txt" }, true );
18. // copy one folder and its contents into another
19. FileUtils.copyDirectoryToDirectory(file1, file2);
20. // delete one folder and its contents
21. 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：

Java代码

1. // create an ArrayList with three arguments
2. List<String> list = Lists.newArrayList("foo" , "bar" , "baz" );
3. // notice that there is no generics or class cast,
4. // and still this line does not generate a warning.
5. Set<String> s = Sets.newConcurrentHashSet();
6. // intersect and union are basic features of a Set, if you ask me
7. Set<String> s = Sets.intersect(s1, s2);
8. // Example of multiple values in a Map
9. ListMultimap<String, Validator> validators = new ArrayListMultimap<String, Validator>();
10. validators.put("save" , new RequiredValidator());
11. validators.put("save" , new StringValidator());
12. validators.put("delete" , new NumberValidator());
13. validators.get("save" ); // { RequiredValidator, StringValidator }
14. validators.get("foo" ); // empty List (not null)
15. 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:

Java代码

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