无法使用Spring的@Value，@ ConfigurationProperties注释从Properties文件中检索值

Question

I am new to Spring Boot and using Spring Annotations. I am trying to build a sample spring boot application in which I get a value for my java property using the properties file. I am trying to use @Component & @ConfigurationProperties parameter. I followed a bunch of tutorials online and this StackOverflow article helped, but my property value is still null

Here is my code.

Looked through:-

1. unable to read properties using configurationproperties annotation

2. https://www.mkyong.com/spring/spring-propertysources-example/

My SpringBoot Application class

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;

@EnableAutoConfiguration
@SpringBootApplication
public class Main {


  public static void main(String[] args) {
    ApplicationContext context =   SpringApplication.run(Main.class, args);
    TestConf t = context.getBean(TestConf.class);
    System.out.println(t.toString());
  }
}

TestConf Class

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Configuration;
import org.springframework.stereotype.Component;

@Component
@ConfigurationProperties("pres")
public class TestConf {

  private String firstName;

  public String getFirstName() {
    return firstName;
  }

  public void setFirstName(String firstName) {
    this.firstName = firstName;
  }

  public TestConf()
  {
    System.out.println("inside constructor");
    System.out.println("first name:" + firstName);
  }


  public static void main(String[] args){
    TestConf t = new TestConf();
  }

  @Override
  public String toString() {
    return "firstName:" + firstName;
  }
}

application.properties

pres.firstName=JACQUELYN

lastly my pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>phil</groupId>
  <artifactId>springTuit</artifactId>
  <version>1.0-SNAPSHOT</version>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.1.2.RELEASE</version>
  </parent>

  <properties>
    <java.version>1.8</java.version>
  </properties>

  <dependencies>

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-thymeleaf</artifactId>
    </dependency>

    <!-- Optional, for bootstrap -->
    <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>bootstrap</artifactId>
      <version>4.3.1</version>
    </dependency>

  </dependencies>
  <build>
    <plugins>
      <!-- Package as an executable jar/war -->
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>2.22.0</version>
      </plugin>
    </plugins>
  </build>

</project>

What is missing to retrieve the value from application.properties correctly into firstName? Does it matter where my application.properties file lies? Although it is in its traditional spot under src/main/resources and my java files are under src/main/java

Answer 1

Code needs couple of minor changes:

@Component
@ConfigurationProperties("classpath:application.properties")
public class TestConf {

  @Value("pres.firstName")
  private String firstName;

Answer 2

This seems standard. However, you can try with the combination

@Component
@PropertySource("classpath:applciation.properties") 
@ConfigurationProperties 

to TestConf.Java

Answer 3

You have two fundamental problems:

1. Your new TestConf() instance isn't a Spring-managed object and thus doesn't get injected at all.

2. Setter (or field) injection inherently means that the values aren't set until after the constructor runs.

If you want to use a Spring bean from some task that gets run when you launch your Boot application, use a CommandLineRunner and inject the bean, preferably with constructor injection.

Answer 4

you can try with the combination..it will work....

@Component
@EnableConfigurationProperties
@ConfigurationProperties(prefix = "pres")
@Data
public class TestConf {

  private String firstName;

.............

}

Answer 5

You can use @Value to get a property's value or as you are trying to fetch the configs using a Configuration class, below example might be helpful.

A Controller class:

@RestController
public class ConfigurationController {

//@Value("${app.name:Movies}") 
//private String name;
//Alternative of configuration class

@Autowired
private Configuration configuration;

@GetMapping("/config")
public MovieConfiguration retrieveConfiguration() {

    return new MovieConfiguration(configuration.getName());
}

A Pojo class

public class MovieConfiguration {

private String name;

public MovieConfiguration(String name) {
    this.name=name;
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}}

A Configuration class

@Component
@ConfigurationProperties("app")
public class Configuration {

private String name;

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}}

Properties

server.port=8091
app.name=SpaceDrama

Answer 6

So it seemed like the reason I did not get my value was not because of the code, but because the port was in use. I thought should not be an issue, but turned out that once I killed the process using the port and ran my application there, everything worked as expected. So my code was correct to begin with..

Thanks for your answers stackoverflow community