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sample code for article "Java Optional As Return Type"

This commit is contained in:
Liesheng Long 2019-05-20 02:24:51 -04:00
parent 2ef9b4eb6f
commit 552b2b2fa9
11 changed files with 315 additions and 1 deletions
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16
core-java-modules/core-java-8-2/pom.xml
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<artifactId>icu4j</artifactId>
<version>${icu.version}</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.4.0.Final</version>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<version>1.4.197</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.9.8</version>
</dependency>
</dependencies>
<build>

41
core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/HandleOptionalTypeExample.java Normal file
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@ -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;
}
}

20
core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/OptionalToJsonExample.java Normal file
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@ -0,0 +1,20 @@
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) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

24
core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/PersistOptionalTypeExample.java Normal file
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@ -0,0 +1,24 @@
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();
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());
}
}

22
core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/PersistOptionalTypeExample2.java Normal file
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@ -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());
}
}

22
core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/PersistUserNoOptionalExample.java Normal file
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package com.baeldung.optionalReturnType;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
public class PersistUserNoOptionalExample {
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());
}
}

42
core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/SerializeOptionalTypeExample.java Normal file
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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();
}
}
}

31
core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/User.java Normal file
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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;
}
}

35
core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/UserOptional.java Normal file
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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);
}
}

31
core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/UserOptionalField.java Normal file
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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;
}
}

32
core-java-modules/core-java-8-2/src/main/resources/META-INF/persistence.xml Normal file
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<?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.UserNoOptional</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>