spring boot - @PostConstruct 未在@Component 上调用

Question

I am new to spring, and I have created a new spring boot project using https://start.spring.io/ with no further dependencies, unzipped the zip file and opened the project in IntelliJ IDEA. I have not done any further configurations. I am now trying to setup a bean with a @PostConstruct method - however, the method is never invoked by spring.

These are my classes:

SpringTestApplication.java

package com.habichty.test.testspring;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

@SpringBootApplication
    public class SpringTestApplication {

        public static void main(String[] args) {
            ConfigurableApplicationContext context = SpringApplication.run(SpringTestApplication.class, args);
            context.getBean(TestBean.class).testMethod();
        }
    }

TestBean.java

package com.habichty.test.testspring;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;
import javax.annotation.PostConstruct;

@Component  
    public class TestBean {
            private final Logger log = LoggerFactory.getLogger(this.getClass());
            private int a = 1;

            public TestBean()
            {
                log.debug("Constructor of TestBean called.");
            }

            @PostConstruct
            public void init()
            {
                log.debug("init()-Method of TestBean called.");
                a = 2;
            }

            public void testMethod()
            {
                log.debug("Test Method of TestBean called. a=" + a);
            }

        }

When I start the application, this is my output:

 :: Spring Boot ::        (v1.5.9.RELEASE)

2018-01-22 13:15:57.960  INFO 12035 --- [           main] c.h.t.testspring.SpringTestApplication   : Starting SpringTestApplication on pbtp with PID 12035 (/home/pat/prj/testspring/testspring/target/classes started by pat in /home/pat/prj/testspring/testspring)
2018-01-22 13:15:57.962 DEBUG 12035 --- [           main] c.h.t.testspring.SpringTestApplication   : Running with Spring Boot v1.5.9.RELEASE, Spring v4.3.13.RELEASE
2018-01-22 13:15:57.962  INFO 12035 --- [           main] c.h.t.testspring.SpringTestApplication   : No active profile set, falling back to default profiles: default
2018-01-22 13:15:58.018  INFO 12035 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@2931522b: startup date [Mon Jan 22 13:15:58 CET 2018]; root of context hierarchy
2018-01-22 13:15:58.510 DEBUG 12035 --- [           main] com.habichty.test.testspring.TestBean    : Constructor of TestBean called.
2018-01-22 13:15:58.793  INFO 12035 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2018-01-22 13:15:58.822  INFO 12035 --- [           main] c.h.t.testspring.SpringTestApplication   : Started SpringTestApplication in 1.073 seconds (JVM running for 2.025)
2018-01-22 13:15:58.822 DEBUG 12035 --- [           main] com.habichty.test.testspring.TestBean    : Test Method of TestBean called. a=1
2018-01-22 13:15:58.826  INFO 12035 --- [       Thread-1] s.c.a.AnnotationConfigApplicationContext : Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@2931522b: startup date [Mon Jan 22 13:15:58 CET 2018]; root of context hierarchy
2018-01-22 13:15:58.828  INFO 12035 --- [       Thread-1] o.s.j.e.a.AnnotationMBeanExporter        : Unregistering JMX-exposed beans on shutdown

As you can see, spring initializes the TestBean and also executes the testMethod() - but the init()-Method, annotated with @PostConstruct, is not invoked.

What am I doing wrong? Any help is very appreciated.

UPDATE 1 In my application.properties, I have configured:

logging.level.com = DEBUG

Changing this to logging.level.root = DEBUG results in a massively bigger log. However, it still does not contain the debug message of my init() method.

UPDATE 2 Added package and import statements.

UPDATE 3 To further clarify that this is not a logging issue, I have added an new int to the code that should be altered by the init()-Method. As far as I understood the concept of the @PostConstruct annotation, it should be executed prior to any other method execution. As a consequence, the output of testMethod() should now contain a=2 . In the updated output, you may see that this is not the case.

UPDATE 4 This is my POM

    <?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>com.habichty.test.testspring</groupId>
    <artifactId>springTest</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>springTest</name>
    <description>springTest</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.9.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

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

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

The output of java -version :

java version "9.0.1"
Java(TM) SE Runtime Environment (build 9.0.1+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)

Answer 1

Due to the new module system in Java9 SpringBoot-1.5.9 fails to process @PostConstruct as the annotation class is not on the classpath. The problem (or similar) is described here and here . There are a few ways to resolve it:

• run the application with Java8,
  or, if still on Java9:
• add javax.annotation:javax.annotation-api dependency to the POM, or
• upgrade to a newer Spring-Boot of version 2.0.0+ (which is still PRERELEASE as of this writing) which incorporates that dependency;

Answer 2

I know this Problem is already solved, but as it is the first Stackoverflow Question that came up when I googled this problem I will leave this here:

I had the same issue and my error was that I had a typo in my package names. My class which was calling name had a different packagename than my SpringBootApplication class. So my main application was not finding my component.

So always check your package names if you have a similiar problems.

Answer 3

I guess you did not define something like

logging.level.root=debug

in your application.properties?

Without = no logs

With =

2018-01-22 12:34:06.117 DEBUG 8516 --- [main] com.example.demo.TestBean  : Constructor of TestBean called. 
...
2018-01-22 12:34:06.117 DEBUG 8516 --- [main] com.example.demo.TestBean : init()-Method of TestBean called. 
...
2018-01-22 12:34:06.241 DEBUG 8516 --- [main]  com.example.demo.TestBean : Test Method of TestBean called.

Answer 4

If you are using Java 9 or higher, then you will encounter an error when using @PostConstruct and @PreDestroy in your code.

Eclipse is unable to import @PostConstruct or @PreDestroy

When using Java 9 and higher, javax.annotation has been removed from its default classpath. That's why Eclipse can't find it.

---

Solution

1. Download the javax.annotation-api-1.3.2.jar from

https://search.maven.org/remotecontent?filepath=javax/annotation/javax.annotation-api/1.3.2/javax.annotation-api-1.3.2.jar

2. Copy the JAR file to the lib folder of your project

---

Use the following steps to add it to your Java Build Path.

3. Right-click your project, select Properties

4. On the left-hand side, click Java Build Path

5. In the top-center of dialog, click Libraries

6. Click Classpath and then Click Add JARs ...

7. Navigate to the JAR file /lib/javax.annotation-api-1.3.2.jar

8. Click OK then click Apply and Close

Eclipse will perform a rebuild of your project and it will resolve the related build errors.