I have a simple Spring boot application that initialize a CLI game.
import com.rpg.game.rpggame.client.RpgGameClient;
#SpringBootApplication
public class RpgGameApplication {
public static void main(String[] args) {
SpringApplication.run(RpgGameApplication.class, args);
RpgGameClient.runGame();
}
}
The runGame() uses some of my services (spring beans).
public class RpgGameClient {
#Autowired
private static GameService gameService;
public static void runGame() {
gameService.createNewGame();
}
}
But I have a NullPointerException when using my service, since Spring can not successfully inject it on my RpgGameClient class.
How can I solve it?
1) RpgGameClient is not declared as a bean candidate. So Spring ignores it.
You can do it by annotating the class with #Component for example (the simplest way) or by declaring a #Bean method that returns the instance of the class.
2) Even with that, it will not work still as #Autowired doesn't work for static fields. Spring injects dependencies into a bean and a bean is an instance of a class.
I think that runGame() should also be non static. Make all static for a bean spring makes no sense. It is the same thing for the Spring boot application class.
3) Constructor injection should be favored to field injection.
So it should be better :
#Component
public class RpgGameClient {
private GameService gameService;
public RpgGameClient(GameService gameService){
this.gameService = gameService;
}
public void runGame() {
gameService.createNewGame();
}
}
And change the Spring Boot app class to use injection dependency such as :
#SpringBootApplication
public class RpgGameApplication {
#Autowired
RpgGameClient rpgGameClient;
#PostConstruct
public void postConstruct(){
rpgGameClient.runGame();
}
public static void main(String[] args) {
SpringApplication.run(RpgGameApplication.class, args);
}
}
Related
I created Spring project via Spring Initializr with project following struct:
I defined property in application.properties file :
my.prop=testvalue
I inject this value into MyClass as following :
#Component
class MyClass {
#Value("${my.prop}")
private String myProp;
public String getMyProp() {
return myProp;
}
}
ConfigBeans defined as following:
package com.example.propertiesdemo;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
#Configuration
public class ConfigBeans {
#Bean
public MyClass myLitoBean() {
return new MyClass();
}
}
PropertiesdemoApplication.java :
package com.example.propertiesdemo;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
#SpringBootApplication
public class PropertiesdemoApplication {
public static void main(String[] args) {
ApplicationContext context
= new AnnotationConfigApplicationContext(
ConfigBeans.class);
MyClass myClass = context.getBean(MyClass.class);
System.out.println(myClass.getMyProp());
}
}
I am expecting that after executing line
System.out.println(myClass.getMyProp());
will be printed value of myprop defined in application.properties (i.e testvalue), but after running (via Netbeans IDE) I get output :
${my.prop}
What was missed / wromg in this code ? Thanks in advance
You are creating MyClass bean twice.
Using #component annotation
using #bean annotation in the config class (use method name lowerCamelCase i.e. in your case myClass())
Create bean only once using any one of the above.
You dont need to create an application context in the main method like this. The presented code is a kind of mixture of "traditional" spring and spring boot. So you're kind of bypassing all the goodies that spring boot offers, among which is automatic application.properties loading.
If you're using spring boot (there is a #SpringBootApplication annotation) then it will create everything by itself.
Usually it should be something like this
public static void main(String[] args) {
SpringApplication.run(PropertiesdemoApplication.class, args);
}
Right, as Navnath Adsul said, you need the bean to be created once, and also, since you are using Spring Boot, you need to raise the context using a special method
#SpringBootApplication
public class PropertiesdemoApplication implements CommandLineRunner {
// Inject Bean
#Autowired
private MyClass myClass;
public static void main(String[] args) {
new SpringApplicationBuilder()
.sources(PropertiesdemoApplication.class)
.run(args);
// or SpringApplication.run(PropertiesdemoApplication.class, args);
}
#Override
public void run(String[] args) throws Exception {
System.out.println(myClass.getMyProp());
}
}
#SpringBootApplication
public class PropertiesdemoApplication {
public static void main(String[] args) {
ApplicationContext context = SpringApplication.run(PropertiesdemoApplication.class, args);
MyClass myClass = context.getBean(MyClass.class);
System.out.println(myClass.getMyProp());
}
}
So I am trying to autowire my http object in my test class and I have tried to integrate with #SpringBootTest however my http object still remains null.
My test class looks like this.
//#RunWith(SpringRunner.class)
#SpringBootTest(classes=Http.class)
public class GetItemTests {
private static final Logger LOGGER = LoggerFactory.getLogger(GetItemTests.class);
#Autowired
private Http httpClass;
}
My SpringBootMain class looks like this
#SpringBootConfiguration
#SpringBootApplication
public class SpringBootMain implements CommandLineRunner {
#Bean
ResourceConfig resourceConfig() {
return new ResourceConfig().registerClasses(Version1Api.class,TokenUtilityClass.class, Paypal.class);
}
#Override
public void run(String... args) throws Exception {
//test.authenticationToken();
}
public static void main(String[] args) {
SpringApplication.run(SpringBootMain.class);
}
}
I have tried running with the SpringRunner as well as this but I receive errors about failing to load the application context.
Unless your Http class is annotated with #Component (meaning it is a bean maintained by the Spring IoC Container) you will not be able to #Autowire it in the way you wrote.
Please also post the exception you are getting and the implementation of your Http class so we can potentially provide further help.
I'm using Kinesis Client Library (KCL) and Spring boot. To use KCL, I have to implement a class (I named it RecordProcessor) for interface IRecordProcessor. And KCL will call this class and process records from kinesis. But when I tried to use dependency injection, I found it was not succeeded.
Here's the snippet for RecordProcessor:
#Component
public class RecordProcessor implements IRecordProcessor {
#Autowired
private SingleRecordProcessor singleRecordProcessor;
#Override
public void initialize(String shardId) {
...
}
#Override
public void processRecords(List<Record> records, IRecordProcessorCheckpointer checkpointer) {
...
}
}
I use Class SingleRecordProcessor to process single each record from kinesis. And this is my SingleRecordProcessor class snippet:
#Component
public class SingleRecordProcessor {
private Parser parser;
private Map<String, Table> tables;
public SingleRecordProcessor() {
}
#Autowired
private void setParser(Parser parser) {
this.parser = parser;
}
#Autowired
private void setTables(Map<String, Table> tables) {
this.tables = tables;
}
public void process(String record) {
...
}
}
I want to let spring framework automatically inject the SingleRecordProcessor instance into the class and use it. But I found that the field singleRecordProcessor is null.
Any idea why the dependency injection is failed? Or is it impossible to inject dependencies into a class which is called by other framework (in this case it's KCL)? Any suggestions will be appreciated! Really need some help please!!
[UPDATE]:
Sorry for not expressing the error clearly. The error was NullPointerException. I tried to inject singleRecordProcessor and call method process() on it. I think the injection was not successful so the instance singleRecordProcessor is null and there comes the NullPointerException.
More information is as follows:
I have a major class called Application
#SpringBootApplication
public class Application{
public static void main(String[] args) {
SpringApplication application = new SpringApplication(Application.class);
application.addListeners(new ApplicationPidFileWriter("./app.pid"));
ConfigurableApplicationContext ctx = application.run(args);
}
}
And I have the MainProcessor class which will call KCL.
#Service
public final class MainProcessor {
#EventListener(ApplicationReadyEvent.class)
public static void startConsumer() throws Exception {
init();
IRecordProcessorFactory recordProcessorFactory = new RecordProcessorFactory();
Worker worker = new Worker(recordProcessorFactory, kinesisClientLibConfiguration);
...
worker.run(); // this line will call KCL library and eventually call ProcessorRecord class.
}
}
[UPDATE2]
RecordProcessorFactory only has one method like this
#Component
public class RecordProcessorFactory implements IRecordProcessorFactory {
#Autowired
RecordProcessor recordProcessor;
#Override
public IRecordProcessor createProcessor() {
return recordProcessor;
}
}
It creates a new RecordProcessor instance for KCL to use it.
You should autowire an instance of this into your MainProcessor:
#Component
public class RecordProcessorFactory {
#Lookup IRecordProcessor createProcessor() { return null; }
}
Spring will instantiate a RecordProcessorFactory for you, and replace the implementation of createProcessor() in it with one that will return a new IRecordProcessor each time it's called. Both the factory and the processors will be Spring beans - which is what you want.
I have the following class, but Spring and MyBatis-Spring-Boot-Starter will not autowire my mapper.
When I run the request, I get the output from the println()
sourceMapper = null
Model
public class Source {
#Autowired
public static SourceMapper sourceMapper; #### Why isn't this set?
public static Source findOrCreate(String url) {
...
System.out.println("sourceMapper = " + sourceMapper);
source = sourceMapper.findByHost(host);
...
}
}
I followed the examples as closely as possible.
http://www.mybatis.org/spring-boot-starter/mybatis-spring-boot-autoconfigure/
The other #Autowired Mappers in the main #Controller class that handles requests work, even though they are private.
This is the Mapper class
package ...mapper;
#Mapper
public interface SourceMapper {
...
I ran into this issue again with a new model and mapper. I tried to follow Why is my Spring #Autowired field null? and the code sample, but it was still null! I tried #Configurable, #Service, #Component.
Model
#Configurable
public class Domain {
#Autowired
private static DomainMapper domainMapper;
public static void incrementCounter(String host) {
...
Domain d = getDomainMapper().find(host, thisMonth);
public static DomainMapper getDomainMapper() {
return domainMapper;
public static void setDomainMapper(DomainMapper domainMapper) {
Domain.domainMapper = domainMapper;
Mapper
#Mapper
public interface DomainMapper {
MyBatis 3.4.5, MyBatis Spring 1.3.1, MyBatis Spring Boot Autoconfigure 1.3.1, MyBatis Spring Boot Starter 1.3.1
I fixed it with
private static DomainMapper getDomainMapper() {
// https://stackoverflow.com/a/52997701/148844
if (domainMapper == null)
domainMapper = MyApplication.getApplicationContext().getBean(DomainMapper.class);
return domainMapper;
And
MyApplication
#Autowired // for AWS
private static ApplicationContext context;
// I believe this only runs during an embedded Tomcat with `mvn spring-boot:run`.
// I don't believe it runs when deploying to Tomcat on AWS.
public static void main(String[] args) {
context = SpringApplication.run(MyApplication.class, args);
But I don't like it!
Spring will only try to inject a bean for you if another bean requires it.
Your class Source is just a normal class with bunch of static methods.
Hence it's not under creation control of Spring.
If you want to inject SourceMapper to your Source, you should mark Source with #Component or #Service so that the container will know it should create a bean of Source type for you and give you an instance of SourceMapper.
Moreover, the SourceMapper should be declared non-static, to prevent if a class access the variable before injected. And static field can be injected only if it use field setter injection.
I have a maven multi module project. When trying to Access a injected bean i get a Nullpointer Exception.
this is the main Function that startsthe application
public class App {
public static void main(String[] args) {
System.out.println("Startpoint");
DecisionMaker decisionMaker = new DecisionMaker();
decisionMaker.run();
}
}
this is what i do in the DecisionMaker
public class DecisionMaker {
#Inject
GameListener gm;
#Inject
BasicProductionManager basicProductionManager;
public DecisionMaker() {
System.out.println("this is the decisionmaker");
System.out.println(gm.toString());
}
so this is not an bean but a normal pojo
the gamelistener is a Applicationscoped bean which i want to inject.
#Named
#ApplicationScoped
public class GameListener extends DefaultBWListener {
#Inject
Event<OnFrameEvent> onFrameEvent;
public Mirror mirror = new Mirror();
public Game game;
public Player self;
#PostConstruct
public void init() {
System.out.println("init listener");
}
the nullpointer gets thrown in the constructor of the DecisionMaker. The #PostConscrutct init method is not called
I looked into similar question but all i found is that i needthe PostConstruct method which i already have.
you can't instantiate DecisionMaker yourself. the whole point of CDI is to give it control of creating and managing beans.
check out this article to see how to use CDI in JAVA SE.