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Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode, for a clean learning experience:

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Once the early-adopter seats are all used, the price will go up and stay at $33/year.

Partner – Microsoft – NPI EA (cat = Baeldung)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Microsoft – NPI EA (cat= Spring Boot)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, you can get started over on the documentation page.

And, you can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Orkes – NPI EA (cat=Spring)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

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Partner – Orkes – NPI EA (tag=Microservices)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

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eBook – Guide Spring Cloud – NPI EA (cat=Spring Cloud)
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eBook – Mockito – NPI EA (tag = Mockito)
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Mocking is an essential part of unit testing, and the Mockito library makes it easy to write clean and intuitive unit tests for your Java code.

Get started with mocking and improve your application tests using our Mockito guide:

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eBook – Java Concurrency – NPI EA (cat=Java Concurrency)
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Handling concurrency in an application can be a tricky process with many potential pitfalls. A solid grasp of the fundamentals will go a long way to help minimize these issues.

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eBook – Reactive – NPI EA (cat=Reactive)
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Spring 5 added support for reactive programming with the Spring WebFlux module, which has been improved upon ever since. Get started with the Reactor project basics and reactive programming in Spring Boot:

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eBook – Java Streams – NPI EA (cat=Java Streams)
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Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.

But these can also be overused and fall into some common pitfalls.

To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:

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eBook – Jackson – NPI EA (cat=Jackson)
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Do JSON right with Jackson

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eBook – HTTP Client – NPI EA (cat=Http Client-Side)
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Get the most out of the Apache HTTP Client

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eBook – Persistence – NPI EA (cat=Persistence)
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Working on getting your persistence layer right with Spring?

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eBook – RwS – NPI EA (cat=Spring MVC)
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Building a REST API with Spring?

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Course – LS – NPI EA (cat=Jackson)
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Get started with Spring and Spring Boot, through the Learn Spring course:

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Course – RWSB – NPI EA (cat=REST)
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Explore Spring Boot 3 and Spring 6 in-depth through building a full REST API with the framework:

>> The New “REST With Spring Boot”

Course – LSS – NPI EA (cat=Spring Security)
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Yes, Spring Security can be complex, from the more advanced functionality within the Core to the deep OAuth support in the framework.

I built the security material as two full courses - Core and OAuth, to get practical with these more complex scenarios. We explore when and how to use each feature and code through it on the backing project.

You can explore the course here:

>> Learn Spring Security

Course – All Access – NPI EA (cat= Spring)
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All Access is finally out, with all of my Spring courses. Learn JUnit is out as well, and Learn Maven is coming fast. And, of course, quite a bit more affordable. Finally.

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Course – LSD – NPI EA (tag=Spring Data JPA)
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Spring Data JPA is a great way to handle the complexity of JPA with the powerful simplicity of Spring Boot.

Get started with Spring Data JPA through the guided reference course:

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Partner – LambdaTest – NPI EA (cat=Testing)
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End-to-end testing is a very useful method to make sure that your application works as intended. This highlights issues in the overall functionality of the software, that the unit and integration test stages may miss.

Playwright is an easy-to-use, but powerful tool that automates end-to-end testing, and supports all modern browsers and platforms.

When coupled with LambdaTest (an AI-powered cloud-based test execution platform) it can be further scaled to run the Playwright scripts in parallel across 3000+ browser and device combinations:

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eBook – Guide Spring Cloud – NPI (cat=Cloud/Spring Cloud)
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1. Overview

In this article, we’ll explore the communication between a front-end application and a REST API that are deployed separately.

The goal is to work around CORS and the Same Origin Policy restriction of the browser and allow the UI to call the API even though they don’t share the same origin.

We’ll basically create two separate applications – a UI application and a simple REST API, and we’ll use the Zuul proxy in the UI application to proxy calls to the REST API.

Zuul is a JVM based router and server side load balancer by Netflix. And Spring Cloud has a nice integration with an embedded Zuul proxy – which is what we’ll use here.

Further reading:

An Example of Load Balancing with Zuul and Eureka

See how load-balancing with Netflix Zuul looks like.

Setting Up Swagger 2 with a Spring REST API Using Springfox

Learn how to document a Spring REST API using Swagger 2.

Introduction to Spring REST Docs

This article introduces Spring REST Docs, a test-driven mechanism to generate documentation for RESTful services that is both accurate and readable.

2. Maven Configuration

First, we need to add a dependency to the zuul support from Spring Cloud to our UI application’s pom.xml:

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-zuul</artifactId>
    <version>2.2.0.RELEASE</version>
</dependency>

The latest version can be found here.

3. Zuul Properties

Next – we need to configure Zuul, and since we’re using Spring Boot, we’re going to do that in the application.yml:

zuul:
  routes:
    foos:
      path: /foos/**
      url: http://localhost:8081/spring-zuul-foos-resource/foos

Note that:

  • We are proxying to our resource server Foos.
  • All requests from the UI that starts with “/foos/” will be routed to our Foos Resource server at http://loclahost:8081/spring-zuul-foos-resource/foos/

4. The API

Our API application is a simple Spring Boot app.

Within this article, we’re going to consider the API deployed in a server running on port 8081.

Let’s first define the basic DTO for the Resource we’re going to be using:

public class Foo {
    private long id;
    private String name;

    // standard getters and setters
}

And a simple controller:

@RestController
public class FooController {

    @GetMapping("/foos/{id}")
    public Foo findById(
      @PathVariable long id, HttpServletRequest req, HttpServletResponse res) {
        return new Foo(Long.parseLong(randomNumeric(2)), randomAlphabetic(4));
    }
}

5. The UI Application

Our UI application is also a simple Spring Boot application.

Within this article, we’re going to consider the API deployed in a server running on port 8080.

Let’s start with the main index.html – using a bit of AngularJS:

<html>
<body ng-app="myApp" ng-controller="mainCtrl">
<script src="angular.min.js"></script>
<script src="angular-resource.min.js"></script>

<script>
var app = angular.module('myApp', ["ngResource"]);

app.controller('mainCtrl', function($scope,$resource,$http) {
    $scope.foo = {id:0 , name:"sample foo"};
    $scope.foos = $resource("/foos/:fooId",{fooId:'@id'});
    
    $scope.getFoo = function(){
        $scope.foo = $scope.foos.get({fooId:$scope.foo.id});
    }  
});
</script>

<div>
    <h1>Foo Details</h1>
    <span>{{foo.id}}</span>
    <span>{{foo.name}}</span>
    <a href="#" ng-click="getFoo()">New Foo</a>
</div>
</body>
</html>

The most important aspect here is how we’re accessing the API using relative URLs!

Keep in mind that the API application isn’t deployed on the same server as the UI application, so relative URLs shouldn’t work, and won’t work without the proxy.

With the proxy, however, we’re accessing the Foo resources through the Zuul proxy, which is of course configured to route these requests to wherever the API is actually deployed.

And finally, the actually Boot enabled application:

@EnableZuulProxy
@SpringBootApplication
public class UiApplication extends SpringBootServletInitializer {

    public static void main(String[] args) {
        SpringApplication.run(UiApplication.class, args);
    }
}

Beyond the simple Boot annotation, notice that we’re using the enable-style of annotation for the Zuul proxy as well, which is pretty cool, clean and concise.

6. Test the Routing

Now – let’s test our UI application – as follows:

@Test
public void whenSendRequestToFooResource_thenOK() {
    Response response = RestAssured.get("http://localhost:8080/foos/1");
 
    assertEquals(200, response.getStatusCode());
}

7. A Custom Zuul Filter

There are multiple Zuul filters available, and we can also create our own custom one:

@Component
public class CustomZuulFilter extends ZuulFilter {

    @Override
    public Object run() {
        RequestContext ctx = RequestContext.getCurrentContext();
        ctx.addZuulRequestHeader("Test", "TestSample");
        return null;
    }

    @Override
    public boolean shouldFilter() {
       return true;
    }
    // ...
}

This simple filter just adds a header called “Test” to the request – but of course, we can get as complex as we need to here augment our requests.

8. Test Custom Zuul Filter

Finally, let’s test make sure our custom filter is working – first we will modify our FooController at Foos resource server:

@RestController
public class FooController {

    @GetMapping("/foos/{id}")
    public Foo findById(
      @PathVariable long id, HttpServletRequest req, HttpServletResponse res) {
        if (req.getHeader("Test") != null) {
            res.addHeader("Test", req.getHeader("Test"));
        }
        return new Foo(Long.parseLong(randomNumeric(2)), randomAlphabetic(4));
    }
}

Now – let’s test it out:

@Test
public void whenSendRequest_thenHeaderAdded() {
    Response response = RestAssured.get("http://localhost:8080/foos/1");
 
    assertEquals(200, response.getStatusCode());
    assertEquals("TestSample", response.getHeader("Test"));
}

9. Conclusion

In this write-up, we focused on using Zuul to route requests from a UI application to a REST API. We successfully worked around CORS and the same-origin policy and we also managed to customize and augment the HTTP request in transit.

The code backing this article is available on GitHub. Once you're logged in as a Baeldung Pro Member, start learning and coding on the project.
Baeldung Pro – NPI EA (cat = Baeldung)
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Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode, for a clean learning experience:

>> Explore a clean Baeldung

Once the early-adopter seats are all used, the price will go up and stay at $33/year.

Partner – Microsoft – NPI EA (cat = Spring Boot)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Orkes – NPI EA (cat = Spring)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

Partner – Orkes – NPI EA (tag = Microservices)
announcement - icon

Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

eBook – HTTP Client – NPI EA (cat=HTTP Client-Side)
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The Apache HTTP Client is a very robust library, suitable for both simple and advanced use cases when testing HTTP endpoints. Check out our guide covering basic request and response handling, as well as security, cookies, timeouts, and more:

>> Download the eBook

eBook – Java Concurrency – NPI EA (cat=Java Concurrency)
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Handling concurrency in an application can be a tricky process with many potential pitfalls. A solid grasp of the fundamentals will go a long way to help minimize these issues.

Get started with understanding multi-threaded applications with our Java Concurrency guide:

>> Download the eBook

eBook – Java Streams – NPI EA (cat=Java Streams)
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Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.

But these can also be overused and fall into some common pitfalls.

To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:

>> Join Pro and download the eBook

eBook – Persistence – NPI EA (cat=Persistence)
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Working on getting your persistence layer right with Spring?

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Course – LS – NPI EA (cat=REST)

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Get started with Spring Boot and with core Spring, through the Learn Spring course:

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Course – Spring Sale 2025 – NPI EA (cat= Baeldung)
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Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:

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Course – Spring Sale 2025 – NPI (All)
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Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:

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Course – LS – NPI (cat=REST)
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Get started with Spring Boot and with core Spring, through the Learn Spring course:

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Partner – Microsoft – NPI (cat=Spring)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

eBook Jackson – NPI EA – 3 (cat = Jackson)
eBook – eBook Guide Spring Cloud – NPI (cat=Cloud/Spring Cloud)