Use DateTimeFormatter to solve the problem of java.lang.NumberFormatException in SimpleDateFormat when multi-threaded

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foreword

A java.lang.NumberFormatException problem occurs when using SimpleDateFormat for date conversion in a multi-threaded situation.

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1. SimpleDateFormat for date conversion

code show as below:

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
for(int i = 0; i < 10; i++){
    
    
	new Thread(() -> {
    
    
		try {
    
    
			log.debug("{}",sdf.parse("1995-09-04"));//log是使用了@Self4j注解
		}catch (Exception e){
    
    
			log.error("{}",e);
		}
	}).start();
}

This code is likely to have java.lang.NumberFormatException problems or incorrect date parsing results, because SimpleDateFormat is not thread-safe.

2. Solution 1: DateTimeFormatter provided by java8

code show as below:

DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd");
for(int i = 0; i < 10; i++){
    
    
	new Thread(() -> {
    
    
		LocalDate date = dtf.parse("1995-09-04",LocalDate::form);
		log.debug("{}",date);
	}).start();
}

You can see that this class is immutable and thread-safe.

3. Solution 2

code show as below:

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
for(int i = 0; i < 10; i++){
    
    
	new Thread(() -> {
    
    
		synchronize (sdf){
    
    
			try {
    
    
				log.debug("{}",sdf.parse("1995-09-04"));//log是使用了@Self4j注解
			}catch (Exception e){
    
    
				log.error("{}",e);
			}
		}
	}).start();
}

Although this can solve the problem, it will cause a loss in performance, so it is not recommended to use it. It is recommended to use method 1.

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