Merge remote-tracking branch 'upstream/master'

2018-08-12 01:59:56 +05:30
parent b96c08f324 b3579151a9
commit f84a17f807
214 changed files with 3125 additions and 1132 deletions
@@ -23,3 +23,4 @@
 - [Converting Between Roman and Arabic Numerals in Java](http://www.baeldung.com/java-convert-roman-arabic)
 - [Practical Java Examples of the Big O Notation](http://www.baeldung.com/java-algorithm-complexity)
 - [Find the Middle Element of a Linked List](http://www.baeldung.com/java-linked-list-middle-element)
+- [An Introduction to the Theory of Big-O Notation](http://www.baeldung.com/big-o-notation)
@@ -0,0 +1,2 @@
+### Relevant Articles:
+- [Guide to Apache Avro](http://www.baeldung.com/java-apache-avro)
@@ -1,5 +1,5 @@
 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.baeldung</groupId>
    <artifactId>apache-cxf</artifactId>
@@ -17,6 +17,7 @@
        <module>cxf-spring</module>
        <module>cxf-jaxrs-implementation</module>
        <module>cxf-aegis</module>
+        <module>sse-jaxrs</module>
    </modules>

    <build>
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>sse-jaxrs</artifactId>
+    <packaging>pom</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>apache-cxf</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+    <modules>
+        <module>sse-jaxrs-server</module>
+        <module>sse-jaxrs-client</module>
+   </modules>
+
+</project>
@@ -0,0 +1,62 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>sse-jaxrs</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>sse-jaxrs-client</artifactId>
+
+    <properties>
+        <cxf-version>3.2.0</cxf-version>
+    </properties>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>exec-maven-plugin</artifactId>
+                <version>1.6.0</version>
+                <executions>
+                    <execution>
+                        <id>singleEvent</id>
+                        <goals>
+                            <goal>java</goal>
+                        </goals>
+                        <configuration>
+                            <mainClass>com.baeldung.sse.jaxrs.client.SseClientApp</mainClass>
+                        </configuration>
+                    </execution>
+                    <execution>
+                        <id>broadcast</id>
+                        <goals>
+                            <goal>java</goal>
+                        </goals>
+                        <configuration>
+                            <mainClass>com.baeldung.sse.jaxrs.client.SseClientBroadcastApp</mainClass>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.cxf</groupId>
+            <artifactId>cxf-rt-rs-client</artifactId>
+            <version>${cxf-version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.cxf</groupId>
+            <artifactId>cxf-rt-rs-sse</artifactId>
+            <version>${cxf-version}</version>
+        </dependency>
+    </dependencies>
+
+</project>
@@ -0,0 +1,48 @@
+package com.baeldung.sse.jaxrs.client;
+
+import javax.ws.rs.client.Client;
+import javax.ws.rs.client.ClientBuilder;
+import javax.ws.rs.client.WebTarget;
+import javax.ws.rs.sse.InboundSseEvent;
+import javax.ws.rs.sse.SseEventSource;
+import java.util.function.Consumer;
+
+public class SseClientApp {
+
+    private static final String url = "http://127.0.0.1:9080/sse-jaxrs-server/sse/stock/prices";
+
+    public static void main(String... args) throws Exception {
+
+        Client client = ClientBuilder.newClient();
+        WebTarget target = client.target(url);
+        try (SseEventSource eventSource = SseEventSource.target(target).build()) {
+
+            eventSource.register(onEvent, onError, onComplete);
+            eventSource.open();
+
+            //Consuming events for one hour
+            Thread.sleep(60 * 60 * 1000);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        client.close();
+        System.out.println("End");
+    }
+
+    // A new event is received
+    private static Consumer<InboundSseEvent> onEvent = (inboundSseEvent) -> {
+        String data = inboundSseEvent.readData();
+        System.out.println(data);
+    };
+
+    //Error
+    private static Consumer<Throwable> onError = (throwable) -> {
+        throwable.printStackTrace();
+    };
+
+    //Connection close and there is nothing to receive
+    private static Runnable onComplete = () -> {
+        System.out.println("Done!");
+    };
+
+}
@@ -0,0 +1,52 @@
+package com.baeldung.sse.jaxrs.client;
+
+import javax.ws.rs.client.Client;
+import javax.ws.rs.client.ClientBuilder;
+import javax.ws.rs.client.WebTarget;
+import javax.ws.rs.sse.InboundSseEvent;
+import javax.ws.rs.sse.SseEventSource;
+import java.util.concurrent.TimeUnit;
+import java.util.function.Consumer;
+
+public class SseClientBroadcastApp {
+
+    private static final String subscribeUrl = "http://localhost:9080/sse-jaxrs-server/sse/stock/subscribe";
+
+
+    public static void main(String... args) throws Exception {
+
+        Client client = ClientBuilder.newClient();
+        WebTarget target = client.target(subscribeUrl);
+        try (final SseEventSource eventSource = SseEventSource.target(target)
+                .reconnectingEvery(5, TimeUnit.SECONDS)
+                .build()) {
+            eventSource.register(onEvent, onError, onComplete);
+            eventSource.open();
+            System.out.println("Wainting for incoming event ...");
+
+            //Consuming events for one hour
+            Thread.sleep(60 * 60 * 1000);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        client.close();
+        System.out.println("End");
+    }
+
+    // A new event is received
+    private static Consumer<InboundSseEvent> onEvent = (inboundSseEvent) -> {
+        String data = inboundSseEvent.readData();
+        System.out.println(data);
+    };
+
+    //Error
+    private static Consumer<Throwable> onError = (throwable) -> {
+        throwable.printStackTrace();
+    };
+
+    //Connection close and there is nothing to receive
+    private static Runnable onComplete = () -> {
+        System.out.println("Done!");
+    };
+
+}
@@ -0,0 +1,85 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>sse-jaxrs</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>sse-jaxrs-server</artifactId>
+    <packaging>war</packaging>
+
+    <properties>
+        <liberty-maven-plugin.version>2.4.2</liberty-maven-plugin.version>
+        <failOnMissingWebXml>false</failOnMissingWebXml>
+        <openliberty-version>18.0.0.2</openliberty-version>
+    </properties>
+
+    <build>
+        <finalName>${artifactId}</finalName>
+        <plugins>
+            <plugin>
+                <groupId>net.wasdev.wlp.maven.plugins</groupId>
+                <artifactId>liberty-maven-plugin</artifactId>
+                <version>${liberty-maven-plugin.version}</version>
+                <configuration>
+                    <assemblyArtifact>
+                        <groupId>io.openliberty</groupId>
+                        <artifactId>openliberty-webProfile8</artifactId>
+                        <version>${openliberty-version}</version>
+                        <type>zip</type>
+                    </assemblyArtifact>
+                    <installAppPackages>project</installAppPackages>
+                    <looseApplication>true</looseApplication>
+                    <configFile>src/main/liberty/config/server.xml</configFile>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>install-server</id>
+                        <phase>prepare-package</phase>
+                        <goals>
+                            <goal>install-server</goal>
+                            <goal>create-server</goal>
+                            <goal>install-feature</goal>
+                        </goals>
+                    </execution>
+                    <execution>
+                        <id>install-apps</id>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>install-apps</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
+    <dependencies>
+
+        <dependency>
+            <groupId>javax.ws.rs</groupId>
+            <artifactId>javax.ws.rs-api</artifactId>
+            <version>2.1</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>javax.enterprise</groupId>
+            <artifactId>cdi-api</artifactId>
+            <version>2.0</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>javax.json.bind</groupId>
+            <artifactId>javax.json.bind-api</artifactId>
+            <version>1.0</version>
+            <scope>provided</scope>
+        </dependency>
+
+    </dependencies>
+
+</project>
@@ -0,0 +1,8 @@
+package com.baeldung.sse.jaxrs;
+
+import javax.ws.rs.ApplicationPath;
+import javax.ws.rs.core.Application;
+
+@ApplicationPath("sse")
+public class AppConfig extends Application {
+}
@@ -0,0 +1,119 @@
+package com.baeldung.sse.jaxrs;
+
+import javax.enterprise.context.ApplicationScoped;
+import javax.inject.Inject;
+import javax.ws.rs.*;
+import javax.ws.rs.core.Context;
+import javax.ws.rs.core.HttpHeaders;
+import javax.ws.rs.core.MediaType;
+import javax.ws.rs.sse.OutboundSseEvent;
+import javax.ws.rs.sse.Sse;
+import javax.ws.rs.sse.SseBroadcaster;
+import javax.ws.rs.sse.SseEventSink;
+
+@ApplicationScoped
+@Path("stock")
+public class SseResource {
+
+    @Inject
+    private StockService stockService;
+
+    private Sse sse;
+    private SseBroadcaster sseBroadcaster;
+    private OutboundSseEvent.Builder eventBuilder;
+
+    @Context
+    public void setSse(Sse sse) {
+        this.sse = sse;
+        this.eventBuilder = sse.newEventBuilder();
+        this.sseBroadcaster = sse.newBroadcaster();
+    }
+
+    @GET
+    @Path("prices")
+    @Produces("text/event-stream")
+    public void getStockPrices(@Context SseEventSink sseEventSink,
+                               @HeaderParam(HttpHeaders.LAST_EVENT_ID_HEADER) @DefaultValue("-1") int lastReceivedId) {
+
+        int lastEventId = 1;
+        if (lastReceivedId != -1) {
+            lastEventId = ++lastReceivedId;
+        }
+        boolean running = true;
+        while (running) {
+            Stock stock = stockService.getNextTransaction(lastEventId);
+            if (stock != null) {
+                OutboundSseEvent sseEvent = this.eventBuilder
+                        .name("stock")
+                        .id(String.valueOf(lastEventId))
+                        .mediaType(MediaType.APPLICATION_JSON_TYPE)
+                        .data(Stock.class, stock)
+                        .reconnectDelay(3000)
+                        .comment("price change")
+                        .build();
+                sseEventSink.send(sseEvent);
+                lastEventId++;
+            }
+            //Simulate connection close
+            if (lastEventId % 5 == 0) {
+                sseEventSink.close();
+                break;
+            }
+
+            try {
+                //Wait 5 seconds
+                Thread.sleep(5 * 1000);
+            } catch (InterruptedException ex) {
+                // ...
+            }
+            //Simulatae a while boucle break
+            running = lastEventId <= 2000;
+        }
+        sseEventSink.close();
+    }
+
+    @GET
+    @Path("subscribe")
+    @Produces(MediaType.SERVER_SENT_EVENTS)
+    public void listen(@Context SseEventSink sseEventSink) {
+        sseEventSink.send(sse.newEvent("Welcome !"));
+        this.sseBroadcaster.register(sseEventSink);
+        sseEventSink.send(sse.newEvent("You are registred !"));
+    }
+
+    @GET
+    @Path("publish")
+    public void broadcast() {
+        Runnable r = new Runnable() {
+            @Override
+            public void run() {
+                int lastEventId = 0;
+                boolean running = true;
+                while (running) {
+                    lastEventId++;
+                    Stock stock = stockService.getNextTransaction(lastEventId);
+                    if (stock != null) {
+                        OutboundSseEvent sseEvent = eventBuilder
+                                .name("stock")
+                                .id(String.valueOf(lastEventId))
+                                .mediaType(MediaType.APPLICATION_JSON_TYPE)
+                                .data(Stock.class, stock)
+                                .reconnectDelay(3000)
+                                .comment("price change")
+                                .build();
+                        sseBroadcaster.broadcast(sseEvent);
+                    }
+                    try {
+                        //Wait 5 seconds
+                        Thread.currentThread().sleep(5 * 1000);
+                    } catch (InterruptedException ex) {
+                        // ...
+                    }
+                    //Simulatae a while boucle break
+                    running = lastEventId <= 2000;
+                }
+            }
+        };
+        new Thread(r).start();
+    }
+}
@@ -0,0 +1,50 @@
+package com.baeldung.sse.jaxrs;
+
+import java.math.BigDecimal;
+import java.time.LocalDateTime;
+
+public class Stock {
+    private Integer id;
+    private String name;
+    private BigDecimal price;
+    LocalDateTime dateTime;
+
+    public Stock(Integer id, String name, BigDecimal price, LocalDateTime dateTime) {
+        this.id = id;
+        this.name = name;
+        this.price = price;
+        this.dateTime = dateTime;
+    }
+
+    public Integer getId() {
+        return id;
+    }
+
+    public void setId(Integer id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public BigDecimal getPrice() {
+        return price;
+    }
+
+    public void setPrice(BigDecimal price) {
+        this.price = price;
+    }
+
+    public LocalDateTime getDateTime() {
+        return dateTime;
+    }
+
+    public void setDateTime(LocalDateTime dateTime) {
+        this.dateTime = dateTime;
+    }
+}
@@ -0,0 +1,78 @@
+package com.baeldung.sse.jaxrs;
+
+import javax.enterprise.context.ApplicationScoped;
+import javax.enterprise.context.Initialized;
+import javax.enterprise.event.Event;
+import javax.enterprise.event.Observes;
+import javax.inject.Inject;
+import javax.inject.Named;
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Random;
+import java.util.concurrent.atomic.AtomicInteger;
+
+@ApplicationScoped
+@Named
+public class StockService {
+
+    private static final BigDecimal UP = BigDecimal.valueOf(1.05f);
+    private static final BigDecimal DOWN = BigDecimal.valueOf(0.95f);
+
+    List<String> stockNames = Arrays.asList("GOOG", "IBM", "MS", "GOOG", "YAHO");
+    List<Stock> stocksDB = new ArrayList<>();
+    private AtomicInteger counter = new AtomicInteger(0);
+
+    public void init(@Observes @Initialized(ApplicationScoped.class) Object init) {
+        //Open price
+        System.out.println("@Start Init ...");
+        stockNames.forEach(stockName -> {
+            stocksDB.add(new Stock(counter.incrementAndGet(), stockName, generateOpenPrice(), LocalDateTime.now()));
+        });
+
+        Runnable runnable = new Runnable() {
+            @Override
+            public void run() {
+                //Simulate Change price and put every x seconds
+                while (true) {
+                    int indx = new Random().nextInt(stockNames.size());
+                    String stockName = stockNames.get(indx);
+                    BigDecimal price = getLastPrice(stockName);
+                    BigDecimal newprice = changePrice(price);
+                    Stock stock = new Stock(counter.incrementAndGet(), stockName, newprice, LocalDateTime.now());
+                    stocksDB.add(stock);
+
+                    int r = new Random().nextInt(30);
+                    try {
+                        Thread.currentThread().sleep(r*1000);
+                    } catch (InterruptedException ex) {
+                        // ...
+                    }
+                }
+            }
+        };
+        new Thread(runnable).start();
+        System.out.println("@End Init ...");
+    }
+
+    public Stock getNextTransaction(Integer lastEventId) {
+        return stocksDB.stream().filter(s -> s.getId().equals(lastEventId)).findFirst().orElse(null);
+    }
+
+    BigDecimal generateOpenPrice() {
+        float min = 70;
+        float max = 120;
+        return BigDecimal.valueOf(min + new Random().nextFloat() * (max - min)).setScale(4,RoundingMode.CEILING);
+    }
+
+    BigDecimal changePrice(BigDecimal price) {
+        return Math.random() >= 0.5 ? price.multiply(UP).setScale(4,RoundingMode.CEILING) : price.multiply(DOWN).setScale(4,RoundingMode.CEILING);
+    }
+
+    private BigDecimal getLastPrice(String stockName) {
+        return stocksDB.stream().filter(stock -> stock.getName().equals(stockName)).findFirst().get().getPrice();
+    }
+}
@@ -0,0 +1,7 @@
+<server description="OpenLiberty Server">
+    <featureManager>
+        <feature>jaxrs-2.1</feature>
+        <feature>cdi-2.0</feature>
+    </featureManager>
+    <httpEndpoint httpPort="9080" httpsPort="9443" id="defaultHttpEndpoint" host="*"/>
+</server>
@@ -0,0 +1,6 @@
+<beans xmlns="http://xmlns.jcp.org/xml/ns/javaee"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
+		http://xmlns.jcp.org/xml/ns/javaee/beans_2_0.xsd"
+       bean-discovery-mode="all">
+</beans>
@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
+    version="4.0">
+    <display-name>Hello Servlet</display-name>
+
+    <welcome-file-list>
+        <welcome-file>index.html</welcome-file>
+    </welcome-file-list>
+
+</web-app>
@@ -0,0 +1 @@
+index
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Server-Sent Event Broadcasting</title>
+</head>
+<body>
+<h2>Stock prices :</h2>
+<div>
+    <ul id="data">
+    </ul>
+</div>
+<script>
+
+    var source = new EventSource('sse/stock/subscribe');
+    source.onopen = function(event) {
+        console.log(event);
+    };
+    source.addEventListener("stock", function(event) {
+        append(event.data);
+    }, false);
+
+    source.onmessage = function(event) {
+        append(event.data);
+    };
+    source.onerror = function(event) {
+        console.log(event);
+    };
+
+    function append(data) {
+        var ul = document.getElementById("data");
+        var li = document.createElement("li");
+        li.appendChild(document.createTextNode(data));
+        ul.insertBefore(li, ul.childNodes[0]);
+    };
+
+</script>
+</body>
+</html>
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Server-Sent Event</title>
+</head>
+<body>
+<h2>Stock prices :</h2>
+<div>
+    <ul id="data">
+    </ul>
+</div>
+<script>
+
+    var source = new EventSource('sse/stock/prices');
+    source.onopen = function(event) {
+        console.log(event);
+    };
+    source.addEventListener("stock", function(event) {
+        append(event.data);
+    }, false);
+
+    source.onmessage = function(event) {
+        append(event.data);
+    };
+    source.onerror = function(event) {
+        console.log(event);
+    };
+
+    function append(data) {
+        var ul = document.getElementById("data");
+        var li = document.createElement("li");
+        li.appendChild(document.createTextNode(data));
+        ul.insertBefore(li, ul.childNodes[0]);
+    };
+
+</script>
+</body>
+</html>
@@ -8,9 +8,10 @@
    <version>1.0-SNAPSHOT</version>

    <parent>
-        <groupId>org.springframework.boot</groupId>
-        <artifactId>spring-boot-starter-parent</artifactId>
-        <version>1.5.2.RELEASE</version>
+        <artifactId>parent-boot-1</artifactId>
+        <groupId>com.baeldung</groupId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../parent-boot-1</relativePath>
    </parent>

    <dependencies>
@@ -10,10 +10,10 @@
    <description>Demo project for Spring Boot</description>

    <parent>
-        <groupId>org.springframework.boot</groupId>
-        <artifactId>spring-boot-starter-parent</artifactId>
-        <version>1.5.13.RELEASE</version>
-        <relativePath /> <!-- lookup parent from repository -->
+        <artifactId>parent-boot-1</artifactId>
+        <groupId>com.baeldung</groupId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-boot-1</relativePath>
    </parent>

    <dependencies>
@@ -3,3 +3,4 @@

 - [Java 10 LocalVariable Type-Inference](http://www.baeldung.com/java-10-local-variable-type-inference)
 - [Guide to Java 10](http://www.baeldung.com/java-10-overview)
+- [Copy a List to Another List in Java](http://www.baeldung.com/java-copy-list-to-another)
@@ -56,4 +56,7 @@
 - [Generalized Target-Type Inference in Java](http://www.baeldung.com/java-generalized-target-type-inference)
 - [Image to Base64 String Conversion](http://www.baeldung.com/java-base64-image-string)
 - [Calculate Age in Java](http://www.baeldung.com/java-get-age)
+- [Copy a List to Another List in Java](http://www.baeldung.com/java-copy-list-to-another)
+- [Increment Date in Java](http://www.baeldung.com/java-increment-date)
 - [Add Hours To a Date In Java](http://www.baeldung.com/java-add-hours-date)
+- [Overriding System Time for Testing in Java](http://www.baeldung.com/java-override-system-time)
@@ -0,0 +1,72 @@
+package com.baeldung.datetime;
+
+import java.text.SimpleDateFormat;
+import java.time.Instant;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import java.time.format.DateTimeFormatter;
+import java.util.Calendar;
+import java.util.Date;
+import java.util.TimeZone;
+
+import org.joda.time.DateTime;
+import org.joda.time.DateTimeZone;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class UseTimeZoneUnitTest {
+
+    /* https://en.wikipedia.org/wiki/List_of_tz_database_time_zones */
+
+    String timeZone = "Asia/Singapore";
+
+    private static final String PATTERN = "E yyyy-MM-dd HH:mm:ss a";
+
+    @Test
+    public void givenDateWithoutTimeZone_WhenSetTimeZoneUsingJava7_ThenTimeZoneIsSetSuccessfully() {
+        Date nowUtc = new Date();
+        TimeZone asiaSingapore = TimeZone.getTimeZone(timeZone);
+
+        Calendar nowAsiaSingapore = Calendar.getInstance(asiaSingapore);
+        nowAsiaSingapore.setTime(nowUtc);
+
+        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(PATTERN);
+        simpleDateFormat.setTimeZone(TimeZone.getTimeZone(timeZone));
+
+        System.out.println(String.format("Java7: Time now in '%s' is '%s'", nowAsiaSingapore.getTimeZone()
+            .getID(), simpleDateFormat.format(nowAsiaSingapore.getTime())));
+        
+        Assert.assertEquals(nowUtc.toInstant().getEpochSecond(), nowAsiaSingapore.toInstant().getEpochSecond());
+        Assert.assertEquals(asiaSingapore, nowAsiaSingapore.getTimeZone());
+
+    }
+
+    @Test
+    public void givenDateWithoutTimeZone_WhenSetTimeZoneUsingJava8_ThenTimeZoneIsSetSuccessfully() {
+        Instant nowUtc = Instant.now();
+        ZoneId asiaSingapore = ZoneId.of(timeZone);
+
+        ZonedDateTime nowAsiaSingapore = ZonedDateTime.ofInstant(nowUtc, asiaSingapore);
+
+        System.out.println(String.format("Java8: Time now in '%s' is '%s'", nowAsiaSingapore.getZone(), 
+            nowAsiaSingapore.format(DateTimeFormatter.ofPattern(PATTERN))));
+
+        Assert.assertEquals(nowUtc.getEpochSecond(), nowAsiaSingapore.toEpochSecond());
+        Assert.assertEquals(asiaSingapore, nowAsiaSingapore.getZone());
+    }
+
+    @Test
+    public void givenDateWithoutTimeZone_WhenSetTimeZoneUsingJodaTime_ThenTimeZoneIsSetSuccessfully() {
+        org.joda.time.Instant nowUtc = org.joda.time.Instant.now();
+        DateTimeZone asiaSingapore = DateTimeZone.forID(timeZone);
+
+        DateTime nowAsiaSingapore = nowUtc.toDateTime(asiaSingapore);
+
+        System.out.println(String.format("Joda-time: Time now in '%s' is '%s'", nowAsiaSingapore.getZone(), 
+            nowAsiaSingapore.toString(PATTERN)));
+        
+        Assert.assertEquals(nowUtc.toInstant().getMillis(), nowAsiaSingapore.toInstant().getMillis());
+        Assert.assertEquals(asiaSingapore, nowAsiaSingapore.getZone());
+    }
+
+}
@@ -31,3 +31,8 @@
 - [How to Store Duplicate Keys in a Map in Java?](http://www.baeldung.com/java-map-duplicate-keys)
 - [Getting the Size of an Iterable in Java](http://www.baeldung.com/java-iterable-size)
 - [Iterating Backward Through a List](http://www.baeldung.com/java-list-iterate-backwards)
+- [How to Filter a Collection in Java](http://www.baeldung.com/java-collection-filtering)
+- [Add Multiple Items to an Java ArrayList](http://www.baeldung.com/java-add-items-array-list)
+- [Remove the First Element from a List](http://www.baeldung.com/java-remove-first-element-from-list)
+- [How to Convert List to Map in Java](http://www.baeldung.com/java-list-to-map)
+- [Initializing HashSet at the Time of Construction](http://www.baeldung.com/java-initialize-hashset)
@@ -0,0 +1,19 @@
+package com.baeldung.nullsafecollectionstreams;
+
+import java.util.Collection;
+import java.util.stream.Stream;
+import static org.apache.commons.collections4.CollectionUtils.emptyIfNull;
+
+public class NullSafeCollectionStreamsUsingCommonsEmptyIfNull {
+
+    /**
+     * This method shows how to make a null safe stream from a collection through the use of
+     * emptyIfNull() method from Apache Commons CollectionUtils library
+     *
+     * @param collection The collection that is to be converted into a stream
+     * @return The stream that has been created from the collection or an empty stream if the collection is null
+     */
+    public Stream<String> collectionAsStream(Collection<String> collection) {
+        return emptyIfNull(collection).stream();
+    }
+}
@@ -0,0 +1,21 @@
+package com.baeldung.nullsafecollectionstreams;
+
+import java.util.Collection;
+import java.util.Optional;
+import java.util.stream.Stream;
+
+public class NullSafeCollectionStreamsUsingJava8OptionalContainer {
+
+    /**
+     * This method shows how to make a null safe stream from a collection  through the use of
+     * Java SE 8’s Optional Container
+     *
+     * @param collection The collection that is to be converted into a stream
+     * @return The stream that has been created from the collection or an empty stream if the collection is null
+     */
+    public Stream<String> collectionAsStream(Collection<String> collection) {
+        return Optional.ofNullable(collection)
+                .map(Collection::stream)
+                .orElseGet(Stream::empty);
+    }
+}
@@ -0,0 +1,19 @@
+package com.baeldung.nullsafecollectionstreams;
+
+import java.util.Collection;
+import java.util.stream.Stream;
+
+public class NullSafeCollectionStreamsUsingNullDereferenceCheck {
+
+    /**
+     * This method shows how to make a null safe stream from a collection through the use of a check
+     * to prevent null dereferences
+     *
+     * @param collection The collection that is to be converted into a stream
+     * @return The stream that has been created from the collection or an empty stream if the collection is null
+     */
+    public Stream<String> collectionAsStream(Collection<String> collection) {
+        return collection == null ? Stream.empty() : collection.stream();
+    }
+
+}
@@ -0,0 +1,26 @@
+package com.baeldung.collection;
+
+import java.util.List;
+import java.util.ArrayList;
+import java.util.Collections;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class CollectionsEmpty {
+
+    @Test
+    public void givenArrayList_whenAddingElement_addsNewElement() {
+        ArrayList<String> mutableList = new ArrayList<>();
+        mutableList.add("test");
+
+        Assert.assertEquals(mutableList.size(), 1);
+        Assert.assertEquals(mutableList.get(0), "test");
+    }
+
+    @Test(expected = UnsupportedOperationException.class)
+    public void givenCollectionsEmptyList_whenAddingElement_throwsUnsupportedOperationException() {
+        List<String> immutableList = Collections.emptyList();
+        immutableList.add("test");
+    }
+
+}
--- a/Show More
+++ b/Show More