Merge pull request #6989 from liesheng/BAEL-2931

sample code for article "Java Optional As Return Type"

core-java-modules/core-java-8-2/pom.xml

@@ -22,6 +22,9 @@
         <maven.compiler.source>1.8</maven.compiler.source>
         <maven.compiler.target>1.8</maven.compiler.target>
         <icu.version>64.2</icu.version>
+        <hibernate.core.version>5.4.0.Final</hibernate.core.version>
+        <h2database.version>1.4.197</h2database.version>
+        <jackson.databind.version>2.9.8</jackson.databind.version>
     </properties>
 
     <dependencies>
@@ -30,7 +33,21 @@
             <artifactId>icu4j</artifactId>
             <version>${icu.version}</version>
         </dependency>
-
+        <dependency>
+            <groupId>org.hibernate</groupId>
+            <artifactId>hibernate-core</artifactId>
+            <version>${hibernate.core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.h2database</groupId>
+            <artifactId>h2</artifactId>
+            <version>${h2database.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>${jackson.databind.version}</version>
+        </dependency>
     </dependencies>
 
     <build>

core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/HandleOptionalTypeExample.java

@@ -0,0 +1,41 @@
+package com.baeldung.optionalReturnType;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+public class HandleOptionalTypeExample {
+    static Map<String, User> usersByName = new HashMap();
+    static {
+        User user1 = new User();
+        user1.setUserId(1l);
+        user1.setFirstName("baeldung");
+        usersByName.put("baeldung", user1);
+    }
+
+    public static void main(String[] args) {
+        changeUserName("baeldung", "baeldung-new");
+        changeUserName("user", "user-new");
+    }
+
+    public static void changeUserName(String oldFirstName, String newFirstName) {
+        Optional<User> userOpt = findUserByName(oldFirstName);
+        if (userOpt.isPresent()) {
+            User user = userOpt.get();
+            user.setFirstName(newFirstName);
+
+            System.out.println("user with name " + oldFirstName + " is changed to " + user.getFirstName());
+        } else {
+            // user is missing
+            System.out.println("user with name " + oldFirstName + " is not found.");
+        }
+    }
+
+    public static Optional<User> findUserByName(String name) {
+        // look up the user in the database, the user object below could be null
+        User user = usersByName.get(name);
+        Optional<User> opt = Optional.ofNullable(user);
+
+        return opt;
+    }
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/OptionalToJsonExample.java

@@ -0,0 +1,19 @@
+package com.baeldung.optionalReturnType;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+public class OptionalToJsonExample {
+    public static void main(String[] args) {
+        UserOptional user = new UserOptional();
+        user.setUserId(1l);
+        user.setFirstName("Bael Dung");
+
+        ObjectMapper om = new ObjectMapper();
+        try {
+            System.out.print("user in json is:" + om.writeValueAsString(user));
+        } catch (JsonProcessingException e) {
+            e.printStackTrace();
+        }
+    }
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/PersistOptionalTypeExample.java

@@ -0,0 +1,26 @@
+package com.baeldung.optionalReturnType;
+
+import java.util.Optional;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+
+public class PersistOptionalTypeExample {
+    static String persistenceUnit = "com.baeldung.optionalReturnType";
+    static EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistenceUnit);
+
+    static EntityManager entityManager = emf.createEntityManager();
+
+    // to run this app, uncomment the follow line in META-INF/persistence.xml
+    // <class>com.baeldung.optionalReturnType.UserOptionalField</class>
+    public static void main(String[] args) {
+        UserOptionalField user1 = new UserOptionalField();
+        user1.setUserId(1l);
+        user1.setFirstName(Optional.of("Bael Dung"));
+        entityManager.persist(user1);
+
+        UserOptional user2 = entityManager.find(UserOptional.class, 1l);
+        System.out.print("User2.firstName:" + user2.getFirstName());
+    }
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/PersistOptionalTypeExample2.java

@@ -0,0 +1,22 @@
+package com.baeldung.optionalReturnType;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+
+public class PersistOptionalTypeExample2 {
+    static String persistenceUnit = "com.baeldung.optionalReturnType";
+    static EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistenceUnit);
+
+    static EntityManager em = emf.createEntityManager();
+
+    public static void main(String[] args) {
+        UserOptional user1 = new UserOptional();
+        user1.setUserId(1l);
+        user1.setFirstName("Bael Dung");
+        em.persist(user1);
+
+        UserOptional user2 = em.find(UserOptional.class, 1l);
+        System.out.print("User2.firstName:" + user2.getFirstName());
+    }
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/PersistUserExample.java

@@ -0,0 +1,22 @@
+package com.baeldung.optionalReturnType;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+
+public class PersistUserExample {
+    static String persistenceUnit = "com.baeldung.optionalReturnType";
+    static EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistenceUnit);
+
+    static EntityManager em = emf.createEntityManager();
+
+    public static void main(String[] args) {
+        User user1 = new User();
+        user1.setUserId(1l);
+        user1.setFirstName("Bael Dung");
+        em.persist(user1);
+
+        User user2 = em.find(User.class, 1l);
+        System.out.print("User2.firstName:" + user2.getFirstName());
+    }
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/SerializeOptionalTypeExample.java

@@ -0,0 +1,41 @@
+package com.baeldung.optionalReturnType;
+
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.ObjectOutputStream;
+import java.util.Optional;
+
+public class SerializeOptionalTypeExample {
+    public static void main(String[] args) {
+        User user1 = new User();
+        user1.setUserId(1l);
+        user1.setFirstName("baeldung");
+
+        serializeObject(user1, "user1.ser");
+
+        UserOptionalField user2 = new UserOptionalField();
+        user2.setUserId(1l);
+        user2.setFirstName(Optional.of("baeldung"));
+
+        serializeObject(user2, "user2.ser");
+
+    }
+
+    public static void serializeObject(Object object, String fileName) {
+        // Serialization
+        try {
+            FileOutputStream file = new FileOutputStream(fileName);
+            ObjectOutputStream out = new ObjectOutputStream(file);
+
+            out.writeObject(object);
+
+            out.close();
+            file.close();
+
+            System.out.println("Object " + object.toString() + " has been serialized to file " + fileName);
+
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/User.java

@@ -0,0 +1,31 @@
+package com.baeldung.optionalReturnType;
+
+import java.io.Serializable;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+
+@Entity
+public class User implements Serializable {
+    @Id
+    private long userId;
+
+    private String firstName;
+
+    public long getUserId() {
+        return userId;
+    }
+
+    public void setUserId(long userId) {
+        this.userId = userId;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/UserOptional.java

@@ -0,0 +1,35 @@
+package com.baeldung.optionalReturnType;
+
+import java.io.Serializable;
+import java.util.Optional;
+
+import javax.persistence.Column;
+import javax.persistence.Entity;
+import javax.persistence.Id;
+
+@Entity
+public class UserOptional implements Serializable {
+    @Id
+    private long userId;
+
+    @Column(nullable = true)
+    private String firstName;
+
+    public long getUserId() {
+        return userId;
+    }
+
+    public void setUserId(long userId) {
+        this.userId = userId;
+    }
+
+    public Optional<String> getFirstName() {
+        return Optional.ofNullable(firstName);
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+        Optional.ofNullable(firstName);
+    }
+
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/UserOptionalField.java

@@ -0,0 +1,31 @@
+package com.baeldung.optionalReturnType;
+
+import java.io.Serializable;
+import java.util.Optional;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+
+@Entity
+public class UserOptionalField implements Serializable {
+    @Id
+    private long userId;
+
+    private Optional<String> firstName;
+
+    public long getUserId() {
+        return userId;
+    }
+
+    public void setUserId(long userId) {
+        this.userId = userId;
+    }
+
+    public Optional<String> getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(Optional<String> firstName) {
+        this.firstName = firstName;
+    }
+}

core-java-modules/core-java-8-2/src/main/resources/META-INF/persistence.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<persistence xmlns="http://java.sun.com/xml/ns/persistence"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
+	version="2.0">
+
+	<persistence-unit
+		name="com.baeldung.optionalReturnType"
+		transaction-type="RESOURCE_LOCAL">
+		<description>Persist Optional Return Type Demo</description>
+		<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
+		<class>com.baeldung.optionalReturnType.User</class>
+		<class>com.baeldung.optionalReturnType.UserOptional</class>
+		<!-- 
+		<class>com.baeldung.optionalReturnType.UserOptionalField</class>
+		-->
+		<exclude-unlisted-classes>true</exclude-unlisted-classes>
+
+		<properties>
+			<property name="javax.persistence.jdbc.driver"
+				value="org.h2.Driver" />
+			<property name="javax.persistence.jdbc.url"
+				value="jdbc:h2:mem:test" />
+			<property name="javax.persistence.jdbc.user" value="sa" />
+			<property name="javax.persistence.jdbc.password" value="" />
+			<property name="hibernate.dialect"
+				value="org.hibernate.dialect.H2Dialect" />
+			<property name="hibernate.hbm2ddl.auto" value="create-drop" />
+			<property name="show_sql" value="true" />
+			<property name="hibernate.temp.use_jdbc_metadata_defaults"
+				value="false" />
+		</properties>
+	</persistence-unit>
+</persistence>