JAVA开发常用类库UUID、Optional、ThreadLocal、TimerTask、Base64使用方法与实例详解

2023-08-01 00:13:05 370

1、UUID类库

UUID根据时间戳实现自动无重复字符串定义

//获取UUID
publicstaticUUIDrandomUUID()

//根据字符串获取UUID
publicstaticUUIDfromString(Stringname)

应用：对文件进行自动命名处理

importjava.util.UUID;

classDemo{

publicstaticvoidmain(String[]args){
System.out.println(UUID.randomUUID());
//85a8ccb1-88f8-4b3c-833d-d45b58e0204e

System.out.println(UUID.fromString("85a8ccb1-88f8-4b3c-833d-d45b58e0204e"));
//85a8ccb1-88f8-4b3c-833d-d45b58e0204e
}
}

2、Optional类库

Optional主要功能是进行null空指针处理

JDK>=1.8

示例：单独处理null参数

classMessage{
privateStringmessage;

publicMessage(Stringmessage){
this.message=message;
}

publicStringgetMessage(){
returnthis.message;
}
}

classDemo{
publicstaticvoidshowMessage(Messagemessage){
if(message!=null){
System.out.println(message.getMessage());
}
}

publicstaticvoidmain(String[]args){
Messagemessage=newMessage("这是消息");
showMessage(message);

showMessage(null);
}
}

几个方法

publicfinalclassOptional{

publicstaticOptionalempty(){
@SuppressWarnings("unchecked")
Optionalt=(Optional)EMPTY;
returnt;
}

publicstaticOptionalof(Tvalue){
returnnewOptional<>(value);
}

publicstaticOptionalofNullable(Tvalue){
returnvalue==null?empty():of(value);
}

publicTget(){
if(value==null){
thrownewNoSuchElementException("Novaluepresent");
}
returnvalue;
}

publicTorElse(Tother){
returnvalue!=null?value:other;
}
}

使用示例

importjava.util.Optional;

/**
*存入
*/
OptionaloptOf=Optional.of("message");
//OptionaloptOfNull=Optional.of(null);
//java.lang.NullPointerException

OptionaloptOfNullable=Optional.ofNullable("message");
OptionaloptOfNullableNull=Optional.ofNullable(null);


/**
*取出
*/
System.out.println(optOf.get());
//message

System.out.println(optOfNullable.get());
//message

//System.out.println(optOfNullableNull.get());
//java.util.NoSuchElementException:Novaluepresent

System.out.println(optOf.orElse("default"));
//message

System.out.println(optOfNullable.orElse("default"));
//message

System.out.println(optOfNullableNull.orElse("default"));
//default

自定义函数实现

classDemo{
publicstaticStringgetDefault(Stringobject,StringdefaultValue){
returnobject!=null?object:defaultValue;
}

publicstaticvoidmain(String[]args){
System.out.println(getDefault("message","default"));
//message

System.out.println(getDefault(null,"default"));
//default
}
}

3、ThreadLocal类库

ThreadLocal解决线程同步问题

publicTget()
publicvoidset(Tvalue)
publicvoidremove()

定义发送消息类

classMessage{
privateStringmessage;

publicMessage(Stringmessage){
this.message=message;
}

publicStringgetMessage(){
returnthis.message;
}
}

classChannel{
privatestaticMessagemessage;

publicstaticvoidsetMessage(Messagemsg){
message=msg;
}

publicstaticvoidsend(){
System.out.println(message.getMessage());
}

}

单线程下运行

classDemo{
publicstaticvoidmain(String[]args){
Messagemessage=newMessage("你好");
Chanel.setMessage(message);
Chanel.send();
//你好
}
}

多线程下运行，出现数据覆盖现象

classDemo{
publicstaticvoidmain(String[]args){
newThread(()->{
Channel.setMessage(newMessage("你好-1"));
Channel.send();
},"线程-1").start();

newThread(()->{
Channel.setMessage(newMessage("你好-2"));
Channel.send();
},"线程-2").start();

newThread(()->{
Channel.setMessage(newMessage("你好-3"));
Channel.send();
},"线程-3").start();
/**
*线程-2你好-3
*线程-1你好-1
*线程-3你好-3
*/
}
}

改造Channel

classChannel{

//privatestaticMessagemessage;
privatestaticfinalThreadLocalTHREAD_LOCAL=newThreadLocal();

publicstaticvoidsetMessage(Messagemsg){
THREAD_LOCAL.set(msg);
}

publicstaticvoidsend(){
System.out.println(Thread.currentThread().getName()
+""
+THREAD_LOCAL.get().getMessage());
}
}

//执行后数据对应
/**

线程-2你好-2
线程-1你好-1
线程-3你好-3
*/

ThreadLocal，只允许保存一个数据

4、TimerTask类库定时调度

定时器进行定时任务处理，实现了一种间隔触发操作

java.util.TimerTask定时任务处理

java.util.Timer任务启动

//定时启动
publicvoidschedule(TimerTasktask,longdelay)

//间隔任务
publicvoidscheduleAtFixedRate(TimerTasktask,longdelay,longperiod)

定义任务

importjava.util.TimerTask;

classMyTaskextendsTimerTask{

@Override
publicvoidrun(){
System.out.println("任务启动"+System.currentTimeMillis());
}
}

示例：定时启动，会卡主

importjava.util.Timer;

classDemo{
publicstaticvoidmain(String[]args){
Timertimer=newTimer();
timer.schedule(newMyTask(),100);
//任务启动1574260837613
}
}

示例：间隔任务

classDemo{
publicstaticvoidmain(String[]args){
Timertimer=newTimer();
timer.scheduleAtFixedRate(newMyTask(),100,1000);
}
}

5、Base64类库加密与解密

加密解密示例

Stringmessage="HelloJava";

StringencodeMessage=newString(Base64.getEncoder().encode(message.getBytes()));

System.out.println(encodeMessage);

//SGVsbG8gSmF2YQ==

StringdecodeMessage=newString(Base64.getDecoder().decode(encodeMessage));

System.out.println(decodeMessage);

//HelloJava

最好的方法是使用2-3中加密程序，进行多次加密