Huong Dan Java - Page 64 of 82 - Java development tutorials

Convert Java object to JSON using Jackson

Jackson is a standard library for handling JSON-related issues in Java. In this tutorial, we will learn how to convert Java objects to JSON using the Jackson library. First, I will illustrate with a Maven project as follows: Jackson dependency is as follows:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.18.1</version>
</dependency>

<groupId>com.fasterxml.jackson.core</groupId>

<artifactId>jackson-databind</artifactId>

</dependency>

The… Read More

flatMap() method of Optional object in Java

8 years ago by Khanh NguyenJava Basic

As you all know, the Optional object is a generic object, its data type can be any object, and therefore, we can meet the case that its data type is also an Optional object, such as: Optional<Optional<String>>. To resolve this problem, Java introduces us to… Read More

isPresent() method of Optional object in Java

8 years ago by Khanh NguyenJava Basic

This method will check whether an Optional object is not empty? If this object is empty, it returns false. For example:

package com.huongdanjava.javaexample;

import java.util.Optional;

public class Example {

	public static void main(String[] args) {
		String s = new String("Khanh");

		Optional<String> opt = Optional.ofNullable(s);
		System.out.println(opt.isPresent());
	}

}

package com.huongdanjava.javaexample;

import java.util.Optional;

public class Example {

public static void main(String[] args) {

String s = new String("Khanh");

Optional<String> opt = Optional.ofNullable(s);

System.out.println(opt.isPresent());

}

Result:

map() method of Optional object in Java

8 years ago by Khanh NguyenJava Basic

This method first will check whether our Optional object is empty or not? If not empty, convert its value to another value. Similar to the filter() method, this method returns an Optional object with a value after conversion. For example:

package com.huongdanjava.javaexample;

import java.util.Optional;

public class Example {

	public static void main(String[] args) {
		String s = new String("Khanh");

		Optional<String> opt = Optional.ofNullable(s);
		opt.map(x -> x.toLowerCase())
			.filter(x -> x.contains("k"))
			.ifPresent(x -> System.out.println("Name: " + x));
	}

}

package com.huongdanjava.javaexample;

import java.util.Optional;

public class Example {

public static void main(String[] args) {

String s = new String("Khanh");

Optional<String> opt = Optional.ofNullable(s);

opt.map(x -> x.toLowerCase())

.filter(x -> x.contains("k"))

.ifPresent(x -> System.out.println("Name: " + x));

}

In the above example,… Read More

filter() method of Optional object in Java

8 years ago by Khanh NguyenJava Basic

This method first will check whether our Optional object is empty or not? If not, then continue to check whether its value meets a certain condition or not? If satisfied, it returns an Optional object containing this value, otherwise returns an empty Optional object. For… Read More

ifPresentOrElse() method of Optional object in Java

8 years ago by Khanh NguyenJava Basic

This method was introduced from Java 9. This method is similar to the ifPresent() method which I introduced in this tutorial, but here is a difference since we have one more Runnable parameter, so that in-case if the Optional object is empty, the object of the… Read More

ifPresent() method of Optional object in Java

8 years ago by Khanh NguyenJava Basic

This method is used to check whether an Optional object is empty or not? If not, then do the operations with this object, otherwise do not do anything. The parameter of this method is an object of the Consumer interface. You can see more about… Read More

Remove Container in Docker

8 years ago by Khanh NguyenDocker

In this tutorial, I will show you all how to remove a Container in Docker. The first is the way to remove a Container. To remove a Container in the Docker, the first thing you need to do is to determine the Container ID or… Read More

Or() methods of Optional object in Java

8 years ago by Khanh NguyenJava Basic

The Optional object in Java has three methods with name start with or(). In this tutorial, we will together learn about them and what is the difference between them. First, I might mention the orElse() method. This method is used to return a default value in… Read More

Learn about Supplier Functional Interface in Java

8 years ago by Khanh NguyenJava Basic

Supplier is a Functional Interface, so it only contains an abstract method as follows:

package java.util.function;

/**
 * Represents a supplier of results.
 *
 * <p>There is no requirement that a new or distinct result be returned each
 * time the supplier is invoked.
 *
 * <p>This is a <a href="package-summary.html">functional interface</a>
 * whose functional method is {@link #get()}.
 *
 * @param <T> the type of results supplied by this supplier
 *
 * @since 1.8
 */
@FunctionalInterface
public interface Supplier<T> {

    /**
     * Gets a result.
     *
     * @return a result
     */
    T get();
}

package java.util.function;

/**

* Represents a supplier of results.

* <p>There is no requirement that a new or distinct result be returned each

* time the supplier is invoked.

* <p>This is a <a href="package-summary.html">functional interface</a>

* whose functional method is {@link #get()}.

* @param <T> the type of results supplied by this supplier

* @since 1.8

@FunctionalInterface

public interface Supplier<T> {

/**

* Gets a result.

* @return a result

T get();

}

This interface simply returns the value in the context that is being used by the get() method. For example, we have the following list:

List<String> s = Arrays.asList("Khanh", "Quan");

1	List<String> s = Arrays.asList("Khanh", "Quan");

Now that I want to… Read More