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Java Spring REST API Sample

Spring for some Java web service client

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Overview

This article introduces how Spring programs works by examining sample programs. Spring projects

Core Spring Professional Certification

VMware, which purchased Pivotal who owns Spring framework, has a “VMware Spring Professional 2021” certification exam (EDU-1202) for $250 USD to answer 60% of 50 Questions in 90 Minutes about core aspects of Spring and Spring Boot. (Previously it was $3,200 USD) Sub-Topics are from the $32,000 USD VMware Spring Professional (EDU-1202) 4-day class, which is no longer mandatory:

  • Configuration: Boot (14%)
    • Introduction to Spring Boot Features
    • Value Proposition of Spring Boot

    • Creating a simple Boot application using Spring Initializer website

    • Java configuration and the Spring application context
    • @Configuration and @Bean annotations
    • @Import: working with multiple configuration files
    • Defining bean scopes

    • Launching a Spring Application and obtaining Beans

    • External properties & Property sources
    • Environment abstraction
    • Using bean profiles
    • Spring Expression Language (SpEL)
  • Component-scanning: Container (28%)
    • Autowiring using @Autowired
    • Java configuration versus annotations, mixing.
    • Lifecycle annotations: @PostConstruct and @PreDestroy

    • Stereotypes and meta-annotations

    • Using Spring FactoryBeans

    • The Spring Bean Lifecycle
    • The BeanFactoryPostProcessor interception point
    • The BeanPostProcessor interception point
    • Spring Bean Proxies
    • @Bean method return types
  • AOP (Aspect Oriented Programming) (14%)
    • What problems does AOP solve?
    • Defining pointcut expressions

    • Implementing various types of advice

    • Overview of Reactive Programming concepts
    • Reactive Programming support in Spring
    • Using Spring’s reactive WebClient
  • Data access (4%) and JDBC (4%)
    • How Spring integrates with existing data access technologies
    • DataAccessException hierarchy

    • Spring‘s JdbcTemplate

    • Quick introduction to ORM with JPA
    • Benefits of using Spring with JPA
    • JPA configuration in Spring
    • Configuring Spring JPA using Spring Boot
    • Spring Data JPA dynamic repositories
  • Database Transactions (10%)
    • Transactions overview
    • Transaction management with Spring
    • Transaction propagation and rollback rules
    • Transactions and integration testing
  • REST (6%) MVC (10%)
    • An introduction to the REST architectural style
    • Controlling HTTP response codes with @ResponseStatus
    • Implementing REST with Spring MVC, @RequestMapping, @RequestBody and @ResponseBody
    • Spring MVC’s HttpMessageConverters and automatic content negotiation
    • Spring GraphQL
  • Spring Security (6%)
    • What problems does Spring Security solve?
    • Configuring authentication
    • Implementing authorization by intercepting URLs
    • Authorization at the Java method level
    • Understanding the Spring Security filter chain

    • Spring security testing

    • OAuth 2 Overview
    • Implementing OAuth 2 using Spring Security OAuth
  • Auto-configuration, Spring Boot Dependencies, and Runtime
    • Dependency management using Spring Boot starters
    • How auto-configuration works
    • Configuration properties
    • Overriding auto-configuration
    • Using CommandLineRunner
  • Actuators, Metrics, and Health Indicators
    • Exposing Spring Boot Actuator endpoints
    • Custom Metrics
    • Health Indicators
    • Creating custom Health Indicators
    • External monitoring systems
  • Spring Boot Testing (4%)
    • Spring and Test-Driven Development
    • Spring 5 integration testing with JUnit 5
    • Application context caching and the @DirtiesContext annotation
    • Profile selection with @ActiveProfiles
    • Easy test data setup with @Sql

Cert prep for Core Spring

BLOG: https://medium.com/javarevisited/top-5-spring-professional-certification-exam-resources-for-java-developers-3ef9fa42fe13

On Udemy:

On Coursera: Building Scalable Java Microservices with Spring Boot and Spring Cloud by Google Cloud’s Sowmya Kannan and Jisha Abubaker. It uses Qwiklabs for GCP App & K8s Engine hands-on running a simple Demo Java Microservices Guestbook application

  • Open another Cloud Shell to create the back end service (defined in GitHub) running on the same Debian host in GCP Cloud Shell within Qwiklabs:

    sh -c "$(curl -fsSL https://raw.githubusercontent.com/wilsonmar/DevSecOps/master/gcp/springboot-guestbook-backend.sh)"

  • Open another Cloud Shell to create the front-end service:

    sh -c "$(curl -fsSL https://raw.githubusercontent.com/wilsonmar/DevSecOps/master/gcp/springboot-guestbook-frontend.sh)"

  • Open another Cloud Shell to test the back-end service REST API:

    sh -c "$(curl -fsSL https://raw.githubusercontent.com/wilsonmar/DevSecOps/master/gcp/springboot-guestbook-testapi.sh)"

  • GCP Cloud SQL database

    sh -c "$(curl -fsSL https://raw.githubusercontent.com/wilsonmar/DevSecOps/master/gcp/springboot-guestbook-cloudsql.sh)"

  • Trace

    springboot-guestbook-trace.sh

  • PubSub async through RabbitMQ, monitored by Google Stack Driver and ZipKin tracing. It only does Create and Update.

On Pluralsight: Spring Framework: Core Spring created in 2020:

David Mayer’s https://www.certification-questions.com/practice-exam/spring/professional?affiliateCode=fcff36fd-557a-4713-abf6-973e9924770f&utm_source=Javin&utm_medium=affiliate&utm_campaign=affiliate

Other Spring certs

Retired:

  • Spring Web Application Developer
  • Spring Integration Specialist using Enterprise Spring

Java Spring Client program

This Java Spring client program that calls a REST API (without authentication, GUI, or database).

This article describes the code while you take a hands-on approach where I introduce concepts after asking you to take an action, so that you have a visual image to go with my commentary.

If any of this doesn’t work for you or doesn’t make sense to you, please reach out to me.

The API response is described at
https://spring.io/guides/gs/consuming-rest

  1. Click on the URL to a REST API written in Spring:

    https://quoters.apps.pcfone.io/api/random

    (previously at https://gturnquist-quoters.cfapps.io/api/random)

    The response:

    The web service returns a JSON document containing a reponse type (“success” or “failure”), an id, and a text string (random quotes about Spring Boot).

    {"type":"success","value":{"id":10,"quote":"Really loving Spring Boot, makes stand alone Spring apps easy."}}

    Alternately:

    "Spring Boot solves this problem. It gets rid of XML and wires up common components for me, so I don't have to spend hours scratching my head just to figure out how it's all pieced together."

    The response is a raw (unformatted) string if you’re using a Google Chrome browser.

    If you are using a FireFox browser, you would see a formatted display such as:

    {
type: "success",
value: {
   id: 10,
   quote: "Really loving Spring Boot, makes stand alone Spring apps easy."
}
}

    Notice there are two levels in the above JSON file:

  2. If you’re using a Firefox browser, you would also see a tab to display HTTP headers it exchanges with servers behind the scenes.

    Sample Spring program source

  3. In an internet browser (Chrome or Firefox), go to:

    https://github.com/spring-guides/gs-consuming-rest

  4. Log into your own GitHub account.

  5. Click Fork because you’ll want to make changes and save it back to GitHub as backup if nothing else.

  6. Install on your laptop the Java Development Kit (JDK), Maven, and Git client software.
  7. Install Atom and Sublime Text for editing files. These are free tools. Commands in this tutorial used “atom” and “subl” to open text files for viewing and edit in context of its folder of other files.

  8. Install Eclipse STS IDE. Also free.

  9. Open a Terminal screen on your operating system (assuming Mac):
  10. Make a folder to hold the new folder to be added.

  11. Get the repository (substituting “spring-guides” with your own account name):

    git clone https://github.com/spring-guides/gs-consuming-rest.git --depth=1
    cd gs-consuming-rest

    NOTE: The account spring-guides is maintained by folks within Pivitol who maintain the spring.io website.

    Structure of folders

  12. View top level folders:

    cd gs-consuming-rest

    There are two folders: “initial” and “complete” so that this repo can be used for learning, with a completed set if changes were made correctly.

  13. View the folders

    cd completed

    Code for two build mechanisms are provided. Use either Maven or Gradle, not both.

    This tutorial makes use of Maven (although Gradle is a simpler, more modern tool).

    Maven to create target .jar

  14. Open to view the pom.xml file which tells the Maven program what artifacts and plugins to download from its Maven Central repository.

    (You can subsitute another editor than Atom)

    atom pom.xml

    <modelVersion>4.0.0</modelVersion> refers to the version of Maven.

    <groupId>org.springframework</groupId><br /> gs-consuming-rest` is used within Eclipse STS.

    java.version 1.8 is required by spring.framework specified as a dependency. (Others substitute a variable ${spring.version}, which is substituted automatically based on the value specified in the tag's content within the same file.)

    jackson provides methods to process JSON files.

    A full application would contain references to libraries to enable use of Tomcat, database, and others.

  15. Assemble all the various files necessary to run into a single .jar file within a target folder.

    On Windows:

    mvnw.cmd

    On Mac:

    chmod +x * ./mvnw

    Run .jar from command line

  16. Run the module (.jar file) created within the target folder:

    cd target
    java -jar gs-consuming-rest-0.1.0.jar

    DEFINITION: A module refers to the way that Java libraries are distributed and used - JAR, WAR, EAR. A .jar file contains all the other files assembled together.

    Although most other Spring apps have a UI, this sample program has only a “console” program with no UI.

    So we look to the console log messages to debug and see whether calls worked.

      .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.5.6.RELEASE)
 
2017-07-30 15:02:46.236  INFO 27820 --- [           main] hello.Application                        : Starting Application v0.1.0 on macs-MacBook-Pro-4.local with PID 27820 (/Users/mac/gits/gs-consuming-rest/complete/target/gs-consuming-rest-0.1.0.jar started by mac in /Users/mac/gits/gs-consuming-rest/complete/target)
2017-07-30 15:02:46.242  INFO 27820 --- [           main] hello.Application                        : No active profile set, falling back to default profiles: default
2017-07-30 15:02:46.365  INFO 27820 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@4b9af9a9: startup date [Sun Jul 30 15:02:46 EDT 2017]; root of context hierarchy
2017-07-30 15:02:47.715  INFO 27820 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2017-07-30 15:02:48.031  INFO 27820 --- [           main] hello.Application                        : Quote{type='success', value=Value{id=7, quote='The real benefit of Boot, however, is that it's just Spring. That means any direction the code takes, regardless of complexity, I know it's a safe bet.'}}
2017-07-30 15:02:48.035  INFO 27820 --- [           main] hello.Application                        : Started Application in 2.501 seconds (JVM running for 3.096)
2017-07-30 15:02:48.035  INFO 27820 --- [       Thread-2] s.c.a.AnnotationConfigApplicationContext : Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@4b9af9a9: startup date [Sun Jul 30 15:02:46 EDT 2017]; root of context hierarchy
2017-07-30 15:02:48.037  INFO 27820 --- [       Thread-2] o.s.j.e.a.AnnotationMBeanExporter        : Unregistering JMX-exposed beans on shutdown

    PROTIP: Ignore the date/time stamps, markers, and warnings in the response. Scroll to the right.

    Notice “hello.Application” is called (even though “No active profile set”). NOTE: Spring Profiles provide a way to segregate parts of your application configuration and make it only available in certain environments.

    After “Registering beans for JMX exposure on startup” notice there is a valid response from the web service over the public internet.

    There is also
    Started Application in 2.501 seconds (JVM running for 3.096)

    Success!

    But how can the program know if the response was successful?

    Test Coding

  17. Look into the src (source) folder:

    cd src
ls -al

    The src/test/java/hello folder contains an ApplicationTest.java file which exercises classes compiled from
    the src/main/java/hello folder.

  18. Use a text editor to look into the ApplicationTest.java file:

    atom test/java/hello/ApplicationTest.java

    Annotations have been processed by the Java compiler since version 5. The compiler looks up the processor associated with each annotation specified. Libraries are imported to enable the use of annotations added above regular code.

    Code to process the @Test annotation is imported from org.springframework.test.context.junit4.SpringRunner.

    The @Test annotation tells JUnit 4 that it can run as a test case the method defined beneath it. This improves upon JUnit 3 which assumes every method is a test if its name starts with “test” and its class extends TestCase.

    JUnit constructs a fresh instance of the class then invokes the annotated method. *

    Exceptions thrown by the test are reported by JUnit as a failure. If no exceptions are thrown, the test is assumed to have succeeded.

    Attributes can be optionally added with annotations:

    To fail a test if the method does NOT throw the named exception:

    @Test(expected = Exception.class)

    To fail a test if the function does not finish with the allotted milliseconds time limit:

    @Test(timeout = 500)

    BTW: Additional annotations @Before/@BeforeClass and @After/@AfterClass are not in JUnit 3.

    Code to process the @SpringBootTest annotation is imported from org.springframework.boot.test.context.SpringBootTest.

    Code to process the @Autowired annotation is imported from org.springframework.beans.factory.annotation.Autowired.

    The RestTemplateBuilder is injected by Spring to perform autoconfiguration (message converters and request factories).

    See http://www.baeldung.com/java-annotation-processing-builder

    See http://qaautomated.blogspot.in/p/junit.html

    (Multiple passes may be necessary to resolve annotations within annotation processor code.)

    PROTIP: Java programs are best read from the bottom of the file.

    At the bottom of the code, the Test program makes an assertThat/strong> restTemplate isNotNull based on code in the org.springframework.web.client.RestTemplate imported.

    @Autowired cause the injection of getter and setter function code automatically during build, to save developer time on the restTemplate. (Any Spring components can be autowired. These include, components, configurations, services and beans.)

    NOTE: A Java Bean is a simple POJO whose only behavior is getters and setters. POJO (Plain Old Java Object) is an object that has attributes as well as behaviors.

    Run Test from Eclipse IDE

    The easiest way of running a single JUnit test method is to run it from within the test case’s class editor within the Eclipse IDE.

  19. Place your cursor on the method’s name inside the test class. I’d recommend using the keyboard to navigate to the method, especially if there are many tests.
  20. To run the test, press Alt+Shift+X,T or right-click, Run As > JUnit Test.

  21. To rerun the same test method, press Ctrl+F11.

    For this to work, ensure that you’ve told Eclipse to always run the last launched application.

    Alternately, go to the Outline view and run the method from there.

    *

    Application.java

    The Java package name defined at the top of the file, hello, puts this in the same package as the Test code described above.

  22. Look into the src (source) folder:

    atom main/java/hello/Application.java

    The entry point into the package is this line of code that appears on all Java programs:

     public static void main(String args[]) {
   ...
 }

    The Application.class is then invoked:

       SpringApplication.run(Application.class);

    ???

    The @SpringBootApplication annotation marks the base package for Spring to begin scanning components. It marks a class for static configurations of the Application Context. And it provides for autoconfiguration to start applying default behaviors.

    The “CommandLineRunner” finishes by issuing an log entry with the code:

    log.info(quote.toString());

    The Logger class imported from the slf1j library takes care of sending lines displayed on your Console.

    Quote.java

    As for the line:

    Quote quote = restTemplate.getForObject(
 "http://gturnquist-quoters.cfapps.io/api/random", Quote.class);

    The “restTemplate” class’s getForObject method is supplied by the Spring Framework.

    “Quote.class” is the response. There must then be a Quote class file to define it.

    The Quote class is defined within the Quote.java file which creates a domain class to specify the data requested.

    Value.java

  23. Look at the bottom of the Quote.java file:

     public String toString() {
     return "Quote{" +
             "type='" + type + '\'' +
             ", value=" + value +
             '}';
 }

    The programmer created this by typing the lines:

     private String type;
 private Value value;

    PROTIP: Set and get funtions can be automatically created within the Eclipse IDE.

    Notice “Value” is not a built-in data type such as “String”, etc. It is a custom type which needs to be defined.

  24. Look in file Value.java which defines the Value type:

     public String toString() {
     return "Value{" +
             "id=" + id +
             ", quote='" + quote + '\'' +
             '}';
 }

    Annotations

    https://docs.spring.io/spring-boot/docs/current/reference/html/

    @Bean provies Bean Factory

    QUESTION: applicationContext.xml file

    “just something you have to do”

##

Data Manipulation Language (DML) is stored in a data.sql file in src > main > resources.

Free Videos about Spring clients

Competitors

JAX-RS - see http://www.java2novice.com/restful-web-services/

Java API for JSON Processing (JSR 353) provides an API to parse, transform, and query JSON data using the object model or the streaming mode. See http://www.java2novice.com/java-json/javax.json/

Google Gson is a Java library that can be used to convert Java Objects into their JSON representation. It can also be used to convert a JSON string to an equivalent Java object. Gson can work with arbitrary Java objects including pre-existing objects that you do not have source-code of. See http://www.java2novice.com/java-json/google-gson/

Java Spring REST API Sample was published on .