類SimpleDateFormat主要負責日期的格式化和轉換，但是在多線程的環境中，使用此類容易造成數據轉換和處理不正確，因為SimpleDateFormat類并不是線程安全的。

• 1簡單示例，出現異常

package com.test.test4;import java.text.SimpleDateFormat;/*** SimpleDateFormat非線程安全* Created by admin on 2018/12/18.*/ public class Test {public static void main(String[] args) {SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");String[]dataStringArray = new String[]{"2000-01-01","2000-01-02","2000-01-03","2000-01-04","2000-01-05"};MyThread[] threadArray = new MyThread[5];for (int i=0;i<5;i++) {threadArray[i] = new MyThread(sdf,dataStringArray[i]);}for (int i=0;i<5;i++) {threadArray[i].start();}}}package com.test.test4;import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date;/*** Created by admin on 2018/12/18.*/ public class MyThread extends Thread {private SimpleDateFormat sdf;private String dateString;public MyThread(SimpleDateFormat sdf,String dateString){super();this.sdf = sdf;this.dateString = dateString;}@Overridepublic void run(){try {Date dateRef = sdf.parse(dateString);String newDateString = sdf.format(dateRef).toString();if (!newDateString.equals(dateString)) {System.out.println("ThreadName="+this.getName()+"報錯了 日期字符串："+dateString+"轉換成的日期為"+newDateString);}} catch (ParseException e) {e.printStackTrace();}}}

• 　　運行結果

ThreadName=Thread-4報錯了 日期字符串：2000-01-05轉換成的日期為0001-01-02 ThreadName=Thread-2報錯了 日期字符串：2000-01-03轉換成的日期為0001-01-02 ThreadName=Thread-0報錯了 日期字符串：2000-01-01轉換成的日期為0001-01-02 ThreadName=Thread-3報錯了 日期字符串：2000-01-04轉換成的日期為0001-01-02Process finished with exit code 0

• 　　解決異常辦法一：解決處理錯誤的原理是創建了多個SimpleDateFormat

public class Test {public static void main(String[] args) {SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");String[]dataStringArray = new String[]{"2000-01-01","2000-01-02","2000-01-03","2000-01-04","2000-01-05"};MyThread[] threadArray = new MyThread[5];for (int i=0;i<5;i++) {threadArray[i] = new MyThread(sdf,dataStringArray[i]);}for (int i=0;i<5;i++) {threadArray[i].start();}}}package com.test.formatOk1;import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date;/*** Created by admin on 2018/12/18.*/ public class DateTools {public static Date parse(String formatPattern, String dataString) throws ParseException{return new SimpleDateFormat(formatPattern).parse(dataString);}public static String format(String formatPattern,Date date){return new SimpleDateFormat(formatPattern).format(date).toString();}}package com.test.formatOk1;import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date;/*** Created by admin on 2018/12/18.*/ public class MyThread extends Thread {private SimpleDateFormat sdf;private String dateString;public MyThread(SimpleDateFormat sdf,String dateString){super();this.sdf = sdf;this.dateString = dateString;}@Overridepublic void run(){try {Date dateRef = DateTools.parse("yyyy-MM-dd",dateString);String newDateString = DateTools.format("yyyy-MM-dd",dateRef).toString();if (!newDateString.equals(dateString)) {System.out.println("ThreadName="+this.getName()+"報錯了 日期字符串："+dateString+"轉換成的日期為"+newDateString);}} catch (ParseException e) {e.printStackTrace();}}}

　　解決異常辦法二：ThreadLocal類能使線程綁定到指定對象，使用ThreadLocal也可以處理這種錯誤

package com.test.formatOk2;import java.text.SimpleDateFormat;/*** SimpleDateFormat非線程安全* Created by admin on 2018/12/18.*/ public class Test {public static void main(String[] args) {SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");String[]dataStringArray = new String[]{"2000-01-01","2000-01-02","2000-01-03","2000-01-04","2000-01-05"};MyThread[] threadArray = new MyThread[5];for (int i=0;i<5;i++) {threadArray[i] = new MyThread(sdf,dataStringArray[i]);}for (int i=0;i<5;i++) {threadArray[i].start();}}}package com.test.formatOk2;import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date;/*** Created by admin on 2018/12/18.*/ public class DateTools {private static ThreadLocal<SimpleDateFormat> t1 = new ThreadLocal<SimpleDateFormat>();public static SimpleDateFormat getSimpleDateFormat(String datePattern){SimpleDateFormat sdf = null;sdf = t1.get();if (sdf == null) {sdf = new SimpleDateFormat(datePattern);t1.set(sdf);}return sdf;}}package com.test.formatOk2;import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date;/*** Created by admin on 2018/12/18.*/ public class MyThread extends Thread {private SimpleDateFormat sdf;private String dateString;public MyThread(SimpleDateFormat sdf,String dateString){super();this.sdf = sdf;this.dateString = dateString;}@Overridepublic void run(){try {Date dateRef = DateTools.getSimpleDateFormat("yyyy-MM-dd").parse(dateString);String newDateString = DateTools.getSimpleDateFormat("yyyy-MM-dd").format(dateRef).toString();if (!newDateString.equals(dateString)) {System.out.println("ThreadName="+this.getName()+"報錯了 日期字符串："+dateString+"轉換成的日期為"+newDateString);}} catch (ParseException e) {e.printStackTrace();}}}

　　

轉載于:https://www.cnblogs.com/airycode/p/10135136.html

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