Java ThreadLocal Thread Security solution _java

The reason why thread-safety problems arise

Thread safety problems are caused by global variables and static variables.

Ii. Thread-safety issues

Simpledateformate SDF = new SimpleDateFormat (); use Sdf.parse (DATESTR); Sdf.format (date); There is a reference to the Caleadar object within the SDF. In the source code sdf.parse (DATESTR); Calendar.clear (); and Calendar.gettime (); Time to get calendar

If thread A calls Sdf.parse () and Calendar.clear () has not executed calendar.gettime (), then thread B calls Sdf.parse (), and thread B executes the Sdf.clear () method , which causes the calendar data for thread A to be emptied;

Threadlocal is to use space to change time, synchronized is to use time to change space

Using threadlocal to resolve thread safety:

public class Threadlocaldateutil {
  private static final String Date_format = "Yyyy-mm-dd HH:mm:ss";
  private static threadlocal<dateformat> ThreadLocal = new threadlocal<dateformat> ();
 
  public static DateFormat GetDateFormat () 
  { 
    DateFormat df = Threadlocal.get (); 
    if (df==null) { 
      df = new SimpleDateFormat (date_format); 
      Threadlocal.set (DF); 
    } 
    return df; 
  } 
  public static String formatdate (date date) throws ParseException {return
    GetDateFormat (). Format (date);
  public static Date Parse (String strdate) throws ParseException {return
    GetDateFormat (). Parse (strdate);
  } 

Using the Synchronized solution:

public class Datesyncutil {
  private static SimpleDateFormat SDF = new SimpleDateFormat ("Yyyy-mm-dd HH:mm:ss");
    
  public static String formatdate (date date) throws parseexception{
    synchronized (SDF) {return
      Sdf.format (date);
    Public
   
  Static Date parse (String strdate) throws parseexception{
    synchronized (SDF) {
      return Sdf.parse (strdate);}}

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