Consuming XML in Spring Boot REST

By default, Spring Boot RESTful web service endpoints consume and produce JSON representations. However, it’s possible to enable consuming XML and producing it for your REST API endpoints with minimal effort. This tutorial will guide you through the process of adding XML support to your Spring Boot application, allowing consuming XML and producing representations of your resources alongside the default JSON representation.

What is a REST API?

A REST (Representational State Transfer) API is a software architecture style that defines a set of constraints to be used when creating web services. It is designed to be simple, lightweight, and scalable. REST APIs are widely used to build web services that can be accessed by other applications, such as mobile apps and web clients, and they support consuming XML as well as other data formats.

REST APIs operate on the HTTP protocol and use a set of standard HTTP methods, such as GET, POST, PUT, and DELETE, to perform CRUD (Create, Read, Update, and Delete) operations on resources. Each resource is identified by a unique URL (Uniform Resource Locator) or URI (Uniform Resource Identifier).

One of the key principles of a REST API is that it is stateless, which means that each request sent to the server must contain all the necessary information to complete the request. The server does not store any client context between requests. This makes REST APIs more scalable and easier to maintain, regardless of whether the client is consuming XML or another data format.

Data types that REST API can return

REST APIs can return different data types depending on the use case and the client’s requirements. Some of the commonly used data types are:

• JSON (JavaScript Object Notation): This is the most commonly used data format for REST APIs. JSON is lightweight, easy to parse, and widely supported by most programming languages. JSON is human-readable and consists of key-value pairs, making it easy to understand and manipulate.
• XML (Extensible Markup Language): XML is another widely used data format for REST APIs. XML is a markup language that is human-readable and machine-readable. It is widely used for data exchange between different platforms and programming languages.
• Plain Text: Plain text is a simple data type that REST APIs can return. It is used for returning simple messages or errors.
• HTML (Hypertext Markup Language): HTML is a data format used for web pages. REST APIs can return HTML pages that can be displayed in a web browser.
• Binary Data: REST APIs can return binary data such as images, audio, and video files.
• CSV (Comma-Separated Values): CSV is a data format used for tabular data. REST APIs can return data in CSV format for easy importing into spreadsheet applications.

In summary, REST APIs can return a variety of data types to meet different requirements. The choice of data type depends on the use case and the client’s needs. JSON and XML are the most commonly used data formats, but REST APIs can also return plain text, HTML, binary data, or CSV.

The Advantages of XML

XML (Extensible Markup Language) is a markup language that has been used for decades to represent structured data in a human-readable and machine-readable format. While XML has been around for a long time, it still offers several advantages that make it a viable choice for certain use cases.

Here are some of the advantages of using XML:

1. Flexibility: XML is an extensible language, meaning that it allows users to define their own elements, attributes, and data types. This flexibility enables developers to create complex document structures and define their own vocabulary for a particular domain.
2. Platform-independent: XML can be parsed and processed by any programming language or platform that supports the language. This makes it an ideal choice for integrating disparate systems or exchanging data between different platforms.
3. Human-readable: XML is designed to be human-readable, which makes it easier for developers and non-technical users to understand the structure and content of the document. This is particularly useful when working with large or complex documents.
4. Validation: XML documents can be validated against a schema or DTD (Document Type Definition) to ensure that they conform to a specific structure and contain the required elements and attributes. This validation helps to reduce errors and improve the overall quality of the data.
5. Compatibility: XML is compatible with many existing tools and technologies, including databases, web services, and middleware. This means that XML can be easily integrated into existing systems without requiring significant changes to the underlying infrastructure.
6. Standardization: XML is a well-established and widely-used standard, which means that there is a large community of developers and users who are familiar with the language. This makes it easier to find support, resources, and tools for working with XML.

In summary, XML is a flexible, platform-independent, human-readable, and standardized format that offers several advantages for representing and exchanging structured data. While it may not be the best choice for every use case, XML remains a viable option for many applications and systems.

The difference between JSON and XML in the context of RESTful web services

In the context of RESTful web services, JSON and XML are two of the most popular data formats used for exchanging data between clients and servers. Both formats have their advantages and disadvantages, and the choice of format depends on the specific requirements and constraints of the application.

JSON (JavaScript Object Notation) is a lightweight data interchange format that is easy to read and write for humans and machines. It is based on a subset of the JavaScript programming language and uses a key-value pair format for data representation. JSON is often used in modern web applications due to its simplicity, speed, and wide support in various programming languages and frameworks.

On the other hand, XML (Extensible Markup Language) is a markup language that allows users to define their own custom tags and structure for data representation, and it’s also an option for consuming XML in Spring Boot RESTful web service endpoints. XML is often used in enterprise applications and document exchange formats due to its rich features, such as validation, namespaces, and schema definition. However, XML is more verbose and complex compared to JSON, which can impact performance and readability in some cases.

In terms of RESTful web services, JSON is generally preferred due to its simplicity, speed, and ease of use in JavaScript-based front-end frameworks. Additionally, JSON is often more compact than XML, which can reduce network bandwidth and improve performance. However, XML is still a valid option for enterprise applications and document exchange formats that require more advanced features, such as validation and schema definition.

Overall, the choice between JSON and XML depends on the specific requirements and constraints of the application. Developers should carefully evaluate the advantages and disadvantages of each format and choose the one that best fits their use case.

Add XML Support to Spring Boot Project

Adding XML support to a Spring Boot project involves configuring the necessary dependencies. There are two main libraries used for XML processing in Spring Boot: Jackson XML and JAXB.

Using Jackson XML

Jackson XML is a library that provides XML support for Jackson, the popular JSON serialization library. To enable consuming xml using Jackson XML in your Spring Boot project, you need to include the following dependencies in your pom.xml file:

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.dataformat/jackson-dataformat-xml -->
<dependency>
    <groupId>com.fasterxml.jackson.dataformat</groupId>
    <artifactId>jackson-dataformat-xml</artifactId>
    <version>${jackson.version}</version>
</dependency>

where ${jackson.version} is the version of the Jackson library that you’re using.

Using JAXB

JAXB is a library that provides XML binding for Java objects, enabling consuming XML data in your Spring Boot project. To add JAXB support, you need to include the following dependency in your pom.xml file:

<dependency>
  <groupId>javax.xml.bind</groupId>
  <artifactId>jaxb-api</artifactId>
  <version>${jaxb.version}</version>
</dependency>

where ${jaxb.version} is the version of the JAXB library that you’re using.

That’s it! With these configurations, your Spring Boot application will have the ability of consuming XML and producing it as well using either Jackson XML or JAXB.

The Content-Type HTTP Header

To inform the web server that the HTTP request body contains XML data and that the server should be capable of consuming XML, you should include the Content-Type header in your request. This header specifies the MIME type of the data being sent and should be set to application/xml. If your Spring Boot application is configured to only accept XML data, the Content-Type header becomes optional.

Here is an example of how to include the Content-Type header in Postman HTTP Client:

1. Open Postman and create a new request.
2. In the Headers section, click on the “Add Row” button to add a new header.
3. In the “Key” column, enter “Content-Type”.
4. In the “Value” column, enter “application/xml”.
5. Send the request with the XML data in the request body.

By including the Content-Type header in your request, you are letting the server know that the request body contains XML data and should be processed accordingly, allowing the server to be capable of consuming XML.

Consuming XML with @PostMapping

Let’s say we have the following code that accepts HTTP POST requests and reads the HTTP request body:

@PostMapping
public UserRest createUser(@RequestBody UserDetailsModelRequest UserDetails) {
    UserRest returnValue = new UserRest();
    
            ...

    return returnValue;
}

To enable the above method to read XML from the HTTP request body and convert it into an object of the UserDetailsModelRequest class, no additional code needs to be written. The method will automatically handle the XML-to-object conversion process, allowing for seamless consuming XML.

However, if we want to configure the above method to accept XML by default, we need to explicitly configure a list of supported media types. In the @PostMapping configuration below, the XML media type is listed first. In this case, if the HTTP request does not contain a Content-Type header, our method will expect consuming XML in the request body.

@PostMapping(
        consumes = { MediaType.APPLICATION_XML_VALUE, MediaType.APPLICATION_JSON_VALUE }, 
        produces = { MediaType.APPLICATION_XML_VALUE, MediaType.APPLICATION_JSON_VALUE }
)

With the @PostMapping annotation configuration shown above, we explicitly specify that our web service endpoint can consume and produce an XML representation of a resource, in addition to the default JSON representation. If a Content-Type header is not included in the request, consuming XML will be expected as the default behavior.

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Conclusion

In this tutorial, we learned how to add XML support to a Spring Boot project using two popular libraries, Jackson XML and JAXB, and explored the importance of the Content-Type HTTP header and the @PostMapping annotation for consuming XML. By understanding the fundamentals of RESTful web services and XML, developers can create robust and scalable applications that can communicate seamlessly with other systems and platforms.

I hope this tutorial has been informative and useful for your understanding of consuming XML in Spring Boot RESTful web services. Don’t forget to check out the Spring Boot tutorials for more related tutorials.

Frequently asked questions

• Can I use both JSON and XML representations in the same RESTful web service endpoint?
  Yes, it is possible to use both JSON and XML representations in the same RESTful web service endpoint. This is commonly known as content negotiation, where the client sends a request with the Accept header specifying the desired representation format, and the server responds with the appropriate content type in the Content-Type header.
• What happens if a client sends a request with an unsupported content type?
  If a client sends a request with an unsupported content type, the server may respond with a “415 Unsupported Media Type” error, indicating that the server is unable to process the request due to an invalid or unsupported content type. It’s important to ensure that the content types supported by the server are clearly documented and communicated to the clients to prevent such errors.
• How do I choose between Jackson XML and JAXB for adding XML support to my Spring Boot project?
  When it comes to choosing between Jackson XML and JAXB for adding XML support to your Spring Boot project, both libraries have their own advantages and disadvantages. JAXB is a widely-used and standard library for XML marshaling and unmarshaling, and is included in the Java standard library. Jackson XML, on the other hand, offers better performance and compatibility with the popular Jackson JSON library, but requires an additional dependency. Ultimately, the choice between the two libraries will depend on your specific project requirements, performance considerations, and personal preference.
• Are there any limitations to the size of XML payloads that can be consumed by Spring Boot RESTful web services?
  Yes, there are some limitations to the size of XML payloads that can be consumed by Spring Boot RESTful web services. The maximum size of a request or response payload can be limited by various factors, such as the server’s available memory, network bandwidth, and the maximum size allowed by the HTTP client and server implementations. Additionally, large XML payloads can also cause performance issues, such as increased processing time and memory usage, which can impact the scalability and reliability of the application.