What is Java API?

In this blog, we will discover everything about APIs in Java. You will learn why APIs are required, along with an example of an API. Afterward, you will see the different types of APIs in Java and different API services. The RESTful API, which is the most popularly used API in Java, will also be discussed with an example.

Table of Contents

• What is an API?
• Introduction to API in Java
• Why is Java API Required?
• Example of an API in Java
• Types of APIs in Java
• API Services
• Popular Java APIs
• RESTful API in Java
• Benefits of API in Java
• How to Secure APIs in Java
• Conclusion
• FAQs

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What is an API?

The term API stands for Application Programming Interface. It is a set of communication protocols and programming code that makes communication between two or more applications possible. It receives the request from the user, sends it to the information provider, and then gets the result from the information provider and sends it to the user. It is like when we search for something online, the API sends the request to the database, and after the data is found in the database, the required result is provided.

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Introduction to API in Java

Before getting to know the API in Java, you should know a little about JDK (Java Development Kit). The JDK file is responsible for delivering APIs in Java. It consists of the compiler, JVM (Java Virtual Machine), and Java API. A compiler converts the high-level language (human-written code) to byte code (machine-understandable) and the JVM provides the output in a human-readable format.

The APIs in Java are integrated into the JDK, which contains classes, interfaces, methods, and fields. It serves as a bridge between the code and the underlying functionalities of the Java platform, offering pre-built components for tasks like I/O operations, networking, database access, GUI development, and more.

Why is Java API Required?

Java APIs are very important for developers as they provide a collection of classes, interfaces, methods, and tools that developers use to build Java applications. It simplifies coding by providing ready-to-use modules, enabling developers to focus on application logic rather than reinventing basic functionalities. Also, APIs in Java let the developers access some third-party services in just a few lines of code.

Sometimes Java APIs may be important for the functionality of an application. Moreover, it helps streamline operating procedures in different applications such as LinkedIn, Instagram, and Twitter by providing multiple options for a user on a single screen.

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Example of an API in Java

To utilize the JDBC API for accessing databases, importing the `java.sql` and `javax.sql` packages is necessary. Once you import them, you can access specific classes within these packages to interact with databases, execute queries, and fetch data as needed within your program. In the following example, we are using received data utilizing the Java JDBC API:

import java.sql.*
import javax.sql.*
import java.sql.Connection;
import java.sql.SQLException;
public static void commit() {    
    Connection con = this.get();    
    if (con != null) {
        try {
           con.commit();        
        } catch (SQLException e) {            
            e.printStackTrace();
            throw new RuntimeException("Transaction related exception occurred while trying to establish a connection…");        
        }
    }
}

This code is designed for managing transactions in a database, where the `commit()` method finalizes a series of database operations, making their changes permanent. Here the ‘commit()’ method is responsible for committing a transaction using the Java JDBC API. The method begins by obtaining a ‘Connection’ object through the ‘this.get()’ method, indicating a connection to a database. Subsequently, it checks if the connection is not null before attempting to commit the transaction using the ‘con.commit()’ statement. In the event of an ‘SQLException’ during the commit process, the code catches the exception, prints the stack trace for debugging purposes, and throws a `RuntimeException` with an informative message. 

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Types of APIs in Java

There are four types of APIs in Java, including:

1. Public APIs: These are also known as Open Java APIs. These types of APIs come included with JDK, so you do not need to install them separately. Also, their use cases are not restricted to some particular area. These APIs are particularly beneficial for organizations that require sharing their data and applications with other organizations for some business strategy.

2. Private APIs: These APIs are created by specific organizations or developers to connect systems and businesses. These can be accessed by authorized people only.

3. Partner APIs: These are the third-party APIs that are offered to organizations for specific business operations.

4. Composite APIs: These APIs are built by combining multiple service APIs and allow up to five API calls in a single request.

API Services

Java APIs provide a wide range of services and functionalities for developers. These services are categorized into the following types:

1. Internal API services: These services are developed for specific organizations and involve complex data operations and internal services. 

2. External API services: These services are integrated by developers into existing applications or websites.

3. User Interface Services: These API services allow developers to build user interfaces for mobiles, computers, and other such devices. 

4. CRUD: CRUD stands for create, read, update, and delete. By using tools like Java Database Connectivity(JDBC), these APIs can perform data manipulation operations over various data storage units such as software as a service (SaaS) and relational database management systems (RDBMS).

Popular Java APIs

Java contains a diverse array of APIs (Application Programming Interfaces) that are used to perform a variety of tasks. Some of the popular APIs in Java include:

• Java API for XML Processing (JAXP): Facilitates XML document processing.
• Java Database Connectivity (JDBC): Empowers Java applications to engage with relational databases.
• Java Naming and Directory Interface (JNDI): Offers naming and directory functionality.
• Java Management Extensions (JMX): Streamlines the management and monitoring of Java applications.
• Java Native Interface (JNI): Permits Java code in a Java Virtual Machine (JVM) to invoke and be invoked by native applications and libraries in other languages.
• Java Servlet API: Manages requests and responses in a web server.
• JavaServer Pages (JSP): Enables the creation of dynamic, platform-independent web content.
• Java Message Service (JMS): Facilitates the creation, sending, receiving, and reading of messages in Java programs.
• Java Persistence API (JPA): Standardizes relational data management in applications.
• Java API for WebSocket: Permits Java applications to communicate over a full-duplex connection in a platform-independent manner.
• Mobile Information Device Profile (MIDP): Tailored for developing applications on mobile devices.
• Connected Limited Device Configuration (CLDC): Outlines the minimum Java runtime requirements for compact consumer devices.
• JavaFX API: Facilitates the creation of rich internet applications, incorporating features like graphics, media, and user interface controls.
• Java Cryptography Architecture (JCA): Establishes a framework and implementation for encryption, key generation, and other security operations.
• Java Authentication and Authorization Service (JAAS): Provides authentication and authorization mechanisms for Java applications.
• Java.net package: Encompasses classes for networking, including sockets and URLs.
• Java Collections Framework (JCF): Offers interfaces and classes for handling collections of objects.
• Java Streams API: Introduced in Java 8, it facilitates functional-style operations on streams of elements.

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RESTful API in Java

A RESTful API (Representational State Transfer) is an architectural style for designing networked applications. RESTful APIs define a set of principles and constraints for the development of scalable, stateless, and maintainable web services. In the Java ecosystem, constructing RESTful APIs is commonly achieved through frameworks such as Spring Boot.

RESTful APIs should possess a uniform and consistent interface. This API demands well-defined conventions for resource naming, the utilization of standard HTTP methods, and a consistent approach to representing resources.

The following example shows the use of the RESTful API in Java using Spring Boot:

@RestController
@RequestMapping("/api/books")
public class BookController {
    @Autowired
    private BookService bookService;
    @GetMapping
    public List<Book> getAllBooks() {
        return bookService.getAllBooks();
    }
    @GetMapping("/{id}")
    public ResponseEntity<Book> getBookById(@PathVariable Long id) {
        Book book = bookService.getBookById(id);
        return book != null ? ResponseEntity.ok(book) : ResponseEntity.notFound().build();
    }
    @PostMapping
    public ResponseEntity<Book> addBook(@RequestBody Book book) {
        Book createdBook = bookService.addBook(book);
    URIlocation=ServletUriComponentsBuilder.fromCurrentRequest().path("/{id}").buildAndExpand(createdBook.getId()).toUri();
        return ResponseEntity.created(location).body(createdBook);
    }
    @PutMapping("/{id}")
    public ResponseEntity<Book> updateBook(@PathVariable Long id, @RequestBody Book updatedBook) {
        Book book = bookService.updateBook(id, updatedBook);
        return book != null ? ResponseEntity.ok(book) : ResponseEntity.notFound().build();
    }
    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteBook(@PathVariable Long id) {
        if (bookService.deleteBook(id)) {
            return ResponseEntity.noContent().build();
        } else {
            return ResponseEntity.notFound().build();
        }
    }
}

This Java code defines a RESTful API using Spring Boot for managing a collection of books. The BookController class, annotated with @RestController and @RequestMapping(“/api/books”), handles various HTTP methods for CRUD operations. It injects a BookService dependency for handling business logic. The endpoints include retrieving all books, getting a book by ID, adding a new book with a POST request, updating a book with a PUT request, and deleting a book with a DELETE request. The use of ResponseEntity provides control over HTTP responses, ensuring proper status codes. 

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Benefits of API in Java

APIs in Java offer many benefits that contribute to the flexibility, efficiency, and scalability of software development. Some advantages of APIs in Java include:

Modularity and Reusability: APIs enable the creation of modular and reusable code components. Developers can design functionalities as separate modules, allowing them to be easily reused in various parts of an application or even in different projects.

Interoperability: APIs facilitate communication between different software components and systems. Java APIs, in particular, promote interoperability by adhering to standardized protocols and data formats, enabling seamless integration with other Java-based systems and diverse technologies.

Abstraction and Encapsulation: APIs provide a level of abstraction and encapsulation, allowing developers to interact with complex systems or libraries without needing to understand their internal workings. This abstraction enhances code readability and reduces the complexity of application development.

Platform Independence: Java APIs are designed to be platform-independent, making it easier to develop applications that can run on various platforms without modification. This platform independence is a result of the “Write Once, Run Anywhere” (WORA) principle associated with Java.

Rapid Development: APIs speed up the development process by providing pre-built functionalities. Developers can leverage existing APIs to implement complex features without having to build them from scratch, resulting in faster development cycles and reduced time-to-market for applications.

Scalability: APIs support scalable application development. As software requirements evolve, developers can extend and enhance applications by integrating new APIs or updating existing ones. This flexibility allows for the seamless growth of applications over time.

Security: APIs help enforce security measures by allowing controlled access to specific functionalities. Authentication and authorization mechanisms can be implemented in APIs to ensure that only authorized users or systems can access certain resources.

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How to Secure APIs in Java

APIs in Java are not very secure; therefore, to make them secure, the developers can implement API security practices by using different security frameworks. There are various frameworks for this purpose. For example, if you are using the REST API in Java, then Apache Shiro is the best security framework for it. This framework can be used to secure any application, including command line applications, mobile applications, or any other large web and enterprise applications. 

Apart from this, Java EE and Spring also provide an efficient security framework for Java APIs. However, to bring these frameworks into action, one has to make tedious efforts. This is why Wallarm is popular. It provides developers with API security solutions that can protect all kinds of Java API, regardless of the type of operating system.

Conclusion

The Java API provides an efficient framework for building applications with more control and customization. On the other hand, RESTful web services offer simplicity, speed, and flexibility, making them popular, especially for scenarios such as mobile app development where fast data processing is crucial. Different platforms and applications might opt for one over the other based on their specific needs and priorities.

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