The most commonly used tool for Java class libraries are summarized.
Apache Commons
Apache Commons subproject there are many commonly used items are as follows.
1、BeanUtils
map and bean interconversion
// bean->map
Map<String, String> map = BeanUtils.describe(user);
// map->bean
BeanUtils.populate(user, map);
We place objects in the cache usually redis in the hash, as follows
设置用户信息
hset student name test
hset student age 10
bean and map the mutual conversion tools is particularly useful in this scenario.
2、Codec
Common coding and decoding methods for encapsulation
// Base64
Base64.encodeBase64String(byte[] binaryData)
Base64.decodeBase64(String base64String)
// MD5
DigestUtils.md5Hex(String data)
// URL
URLCodec.decodeUrl(byte[] bytes);
URLCodec.encodeUrl(BitSet urlsafe, byte[] bytes);
3、Collections
Pay and poor operation
// 判空
CollectionUtils.isEmpty(collA);
// 交集
CollectionUtils.retainAll(collA, collB);
// 并集
CollectionUtils.union(collA, collB);
// 差集
CollectionUtils.subtract(collA, collB);
// 判等
CollectionUtils.isEqualCollection(collA, collB);
4, I / O
Package for IO operations IOUtils
// 拷贝流
IOUtils.copy(InputStream input, OutputStream output);
// 从流中读取内容，转为list
List<String> line = IOUtils.readLines(InputStream input, Charset encoding);
FileUtils package file operation class
File file = new File("/show/data.text");
// 按行读取文件
List<String> lines = FileUtils.readLines(file, "UTF-8");
// 将字符串写入文件
FileUtils.writeStringToFile(file, "test", "UTF-8");
// 文件复制
FileUtils.copyFile(srcFile, destFile);
5, Lang
StringUtils following assertion by testing
// isEmpty的实现 cs == null || cs.length() == 0; return true
assertEquals(true, StringUtils.isEmpty(""));
assertEquals(true, StringUtils.isBlank(null));
assertEquals(true, StringUtils.isBlank(""));
// 空格
assertEquals(true, StringUtils.isBlank(" "));
// 回车
assertEquals(true, StringUtils.isBlank(" "));
Pair and Triple
When two or three want to return values, but no correlation between several values, there is no need for a separate package an object, it can be used as a data structure, or return Pair Triple objects.
Google Guava
Create a collection of
// 普通集合的创建
List<String> list = Lists.newArrayList();
Set<String> set = Sets.newHashSet();
// 不可变集合的创建
ImmutableList<String> list = ImmutableList.of("a", "b", "c");
ImmutableSet<String> set = ImmutableSet.of("a", "b");
Immutable set of thread-safe, and can not be changed midway, because add other methods are declared as expired and will throw an exception
public final void add(int index, E element) {
throw new UnsupportedOperationException();
}
Collection of all kinds of Black &
// use java
Map<String, List<Integer>> map = new HashMap<String, List<Integer>>();
// use guava
Multimap<String, Integer> map = ArrayListMultimap.create();
map.put("key1", 1);
map.put("key1", 2);
System.out.println(map.get("key1")); // [1, 2]
2 a key mapping value
Table<String, String, Integer> table = HashBasedTable.create();
table.put("a", "a", 1);
table.put("a", "b", 2);
System.out.println(table.get("a", "b")); // 2
There are many other types of collections, will not be described
stop watch to see the running time of a section of code
Stopwatch stopwatch = Stopwatch.createStarted();
// do something
long second = stopwatch.elapsed(TimeUnit.SECONDS);
TimeUnit can specify the time precision.
Joda Time
Before jdk1.8, only the date operating common class java.util.Date and java.util.Calendar, but the ease of use of these two classes is very bad, SimpleDateFormat is not thread safe. This forced users to choose the date of the operation of third-party class, Joda Time is one of the best. Later, Java itself is aware of this problem, so jdk1.8 borrows heavily from the Joda Time concept, we launched a new date api, LocalDate, LocalTime, LocalDateTime and so on.
