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‎tls/src/main/java/com/iluwatar/tls/App.java‎

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/**
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* The MIT License
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* Copyright (c) 2016 Thomas Bauer
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.tls;
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import java.util.ArrayList;
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import java.util.Calendar;
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import java.util.Collections;
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import java.util.Date;
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import java.util.List;
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/**
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* ThreadLocal pattern
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* <p>
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* This App shows how to create an isolated space per each thread. In this
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* example the usage of SimpleDateFormat is made to be thread-safe. This is an
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* example of the ThreadLocal pattern.
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* <p>
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* By applying the ThreadLocal pattern you can keep track of application
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* instances or locale settings throughout the handling of a request. The
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* ThreadLocal class works like a static variable, with the exception that it is
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* only bound to the current thread! This allows us to use static variables in a
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* thread-safe way.
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* <p>
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* In Java, thread-local variables are implemented by the ThreadLocal class
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* object. ThreadLocal holds variable of type T, which is accessible via get/set
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* methods.
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* <p>
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* SimpleDateFormat is one of the basic Java classes and is not thread-safe. If
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* you do not isolate the instance of SimpleDateFormat per each thread then
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* problems arise. These problems are described with the example {@link AppUgly}
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*
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*/
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public class App {
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// A list to collect the date values created in the the threads
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static List<Date> dateList = Collections.synchronizedList(new ArrayList<Date>());
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// A list to collect Exceptions thrown in the threads (should be none in
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// this example)
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static List<String> exceptionList = Collections.synchronizedList(new ArrayList<String>());
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/**
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* Program entry point
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*
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* @param args
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* command line args
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*/
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public static void main(String[] args) {
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int counterDateValues = 0;
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int counterExceptions = 0;
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// Create a runnable
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DateFormatRunnable runnableDf = new DateFormatRunnable("dd/MM/yyyy", "15/12/2015");
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// start 4 threads, each using the same Runnable instance
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Thread t1 = new Thread(runnableDf);
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Thread t2 = new Thread(runnableDf);
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Thread t3 = new Thread(runnableDf);
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Thread t4 = new Thread(runnableDf);
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t1.start();
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t2.start();
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t3.start();
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t4.start();
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try {
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t1.join();
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t2.join();
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t3.join();
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t4.join();
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} catch (InterruptedException e) {
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// Action not coded here
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}
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for (Date dt : dateList) {
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// a correct run should deliver 20 times 15.12.2015
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counterDateValues++;
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Calendar cal = Calendar.getInstance();
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cal.setTime(dt);
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// Formatted output of the date value: DD.MM.YYYY
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System.out.println(
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cal.get(Calendar.DAY_OF_MONTH) + "." + cal.get(Calendar.MONTH) + "." + +cal.get(Calendar.YEAR));
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}
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for (String ex : exceptionList) {
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// a correct run shouldn't deliver any exception
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counterExceptions++;
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System.out.println(ex);
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}
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System.out.println("The List dateList contains " + counterDateValues + " date values");
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System.out.println("The List exceptionList contains " + counterExceptions + " exceptions");
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}
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}

‎tls/src/main/java/com/iluwatar/tls/AppUgly.java‎

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/**
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* The MIT License
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* Copyright (c) 2016 Thomas Bauer
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.tls;
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import java.util.ArrayList;
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import java.util.Calendar;
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import java.util.Collections;
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import java.util.Date;
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import java.util.List;
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/**
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*
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* This App shows an example for problems with global thread variables. A global
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* thread variable is a variable defined as class variable of a
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* XyzRunnable-Class. In this example in the class
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* {@link DateFormatUglyRunnable}
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* <p>
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* Example use case: A well known problem with threads are non thread-safe Java
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* classes. One example is the class SimpleDateFormat.
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* <p>
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* In the example an instance of SimpleDateFormat is created in the constructor
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* of the Runnable. The constructor initializes a class variable with the
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* instance. The Runnable only does convert a string date to a date format using
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* the instance of SimpleDateFormat. It does this 5 times.
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* <p>
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* In the example 4 threads are started to do the same. If you are lucky
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* everything works well. But if you try more often you will happen to see
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* Exceptions. And these Exceptions arise on arbitrary points of the run.
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* <p>
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* The reason for this exceptions is: The threads try to use internal instance
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* variables of the SimpleDateFormat instance at the same time (the date is
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* stored internal as member variable during parsing and may be overwritten by
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* another thread during a parse is still running)
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* <p>
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* And even without Exceptions the run may not deliver the correct results.
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* All date values should be the same after the run. Check it
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*
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*/
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public class AppUgly {
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// A list to collect the date values created in the the threads
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static List<Date> dateList = Collections.synchronizedList(new ArrayList<Date>());
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// A list to collect Exceptions thrown in the threads
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static List<String> exceptionList = Collections.synchronizedList(new ArrayList<String>());
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/**
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* Program entry point
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*
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* @param args
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* command line args
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*/
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public static void main(String[] args) {
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int counterDateValues = 0;
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int counterExceptions = 0;
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// Prepare the Runnable
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DateFormatUglyRunnable runnableDf = new DateFormatUglyRunnable("dd/MM/yyyy", "15/12/2015");
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// 4 threads using the same Runnable
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Thread t1 = new Thread(runnableDf);
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Thread t2 = new Thread(runnableDf);
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Thread t3 = new Thread(runnableDf);
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Thread t4 = new Thread(runnableDf);
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t1.start();
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t2.start();
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t3.start();
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t4.start();
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try {
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t1.join();
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t2.join();
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t3.join();
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t4.join();
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} catch (InterruptedException e) {
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// Action not coded here
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}
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for (Date dt : dateList) {
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// a correct run should deliver 20 times 15.12.2015
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counterDateValues++;
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Calendar cal = Calendar.getInstance();
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cal.setTime(dt);
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// Formatted output of the date value: DD.MM.YYYY
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System.out.println(cal.get(Calendar.DAY_OF_MONTH) + "." + cal.get(Calendar.MONTH) + "." + cal.get(Calendar.YEAR));
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}
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for (String ex : exceptionList) {
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// a correct run shouldn't deliver any exception
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counterExceptions++;
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System.out.println(ex);
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}
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System.out.println("The List dateList contains " + counterDateValues + " date values");
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System.out.println("The List exceptionList contains " + counterExceptions + " exceptions");
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}
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}

‎tls/src/main/java/com/iluwatar/tls/DateFormatRunnable.java‎

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/**
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* The MIT License
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* Copyright (c) 2016 Thomas Bauer
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.tls;
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import java.text.DateFormat;
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import java.text.SimpleDateFormat;
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/**
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* DateFormatRunnable converts string dates to a date format using
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* SimpleDateFormat The date format and the date value will be passed to the
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* Runnable by the constructor. The constructor creates a instance of
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* SimpleDateFormat and stores it in a ThreadLocal class variable. For the
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* complete description of the example see {@link App}
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*
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*/
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public class DateFormatRunnable implements Runnable {
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// class variables (members)
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private ThreadLocal<DateFormat> df;
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private String dateValue; // for date Value Thread Local not needed
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/**
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* The date format and the date value are passed to the constructor
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*
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* @param inDateFormat
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* string date format string, e.g. "dd/MM/yyyy"
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* @param inDateValue
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* string date value, e.g. "21/06/2016"
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*/
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public DateFormatRunnable(String inDateFormat, String inDateValue) {
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final String idf = inDateFormat;
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this.df = new ThreadLocal<DateFormat>() {
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@Override
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protected DateFormat initialValue() {
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return new SimpleDateFormat(idf);
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}
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};
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this.dateValue = inDateValue;
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}
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/**
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* @see java.lang.Runnable#run()
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*/
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@Override
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public void run() {
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System.out.println(Thread.currentThread() + " started executing...");
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// Convert date value to date 5 times
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for (int i = 1; i <= 5; i++) {
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try {
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// this is the statement where it is important to have the
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// instance of SimpleDateFormat locally
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// Create the date value and store it in dateList
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App.dateList.add(this.df.get().parse(this.dateValue));
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} catch (Exception e) {
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// write the Exception to a list and continue work
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App.exceptionList.add(e.getClass() + ": " + e.getMessage());
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}
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}
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System.out.println(Thread.currentThread() + " finished executing");
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}
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}

‎tls/src/main/java/com/iluwatar/tls/DateFormatUglyRunnable.java‎

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/**
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* The MIT License
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* Copyright (c) 2016 Thomas Bauer
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
7+
* in the Software without restriction, including without limitation the rights
8+
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
9+
* copies of the Software, and to permit persons to whom the Software is
10+
* furnished to do so, subject to the following conditions:
11+
*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17+
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
18+
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19+
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.tls;
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import java.text.DateFormat;
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import java.text.SimpleDateFormat;
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/**
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* DateFormatUglyRunnable converts string dates to a date format using
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* SimpleDateFormat. The date value and the date format will be passed to the
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* Runnable by the constructor. The constructor creates an instance of
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* SimpleDateFormat and stores it in a class variable. For the complete
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* description of the example see {@link AppUgly}
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*
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*/
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public class DateFormatUglyRunnable implements Runnable {
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// class variables (members)
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private DateFormat df;
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private String dateValue;
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/**
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* The date format and the date value are passed to the constructor
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*
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* @param inDateFormat
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* string date format string, e.g. "dd/MM/yyyy"
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* @param inDateValue
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* string date value, e.g. "21/06/2016"
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*/
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public DateFormatUglyRunnable(String inDateFormat, String inDateValue) {
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this.df = new SimpleDateFormat(inDateFormat);
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this.dateValue = inDateValue;
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}
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/**
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* @see java.lang.Runnable#run()
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*/
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@Override
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public void run() {
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System.out.println(Thread.currentThread() + " started executing...");
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// Convert date value to date 5 times
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for (int i = 1; i <= 5; i++) {
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try {
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// Create the date value and store it in dateList
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AppUgly.dateList.add(this.df.parse(this.dateValue));
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} catch (Exception e) {
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// write the Exception to a list and continue work
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AppUgly.exceptionList.add(e.getClass() + ": " + e.getMessage());
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}
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}
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System.out.println(Thread.currentThread() + " finished executing");
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}
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}

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