What are the ways to initialize Spring at startup？
- 2021-09-11 20:30:26
- OfStack
1. Several ways to initialize Spring when it starts up
Accurately, it is several initialization methods after spring container instantiation is completed. Why do you say that? Look at the following face example:
@Slf4j
@Component
public class InitBeanDemo {
@Autowired
private Environment env;
public InitBeanDemo() {
log.info("DefaultProfiles: {}", Arrays.asList(env.getDefaultProfiles()));
log.info("ActiveProfiles: {}", Arrays.asList(env.getActiveProfiles()));
}
Example is in the bean construction method to do some initialization work, the example is relatively simple only do log print. The ideal is very plump, the reality is very skinny, and the error is reported: Constructor threw exception;; nested exception is java. lang. NullPointerException.
The reason is that Environment has not been initialized yet.
Next, let's explore which initialization methods under 1 can meet the requirements of the above example.
2. Initialize in the constructor
It can run normally, and the execution time is the earliest among all initialization modes. The principle is that Environment is instantiated before InitBeanDemo is instantiated.
@Component
public class InitBeanDemo {
private final Environment env;
@Autowired
public InitBeanDemo (Environment environment) {
this.env = environment;
log.info("Constructor DefaultProfiles: {}", Arrays.asList(env.getDefaultProfiles()));
log.info("Constructor ActiveProfiles: {}", Arrays.asList(env.getActiveProfiles()));
}
}
3. Regular 3-piece set
Regular 3-piece set: @ PostConstruct, InitializingBean, initMethod. If you like, three methods can be used under the same Bean at the same time, and the priority of execution is @ PostConstruct > InitializingBean > initMethod.
@ PostConstruct notes
In one that can be scanned to Bean, add an public void xxx () method with @ PostConstruct annotation, and write the logic to be initialized in the method.
You can have multiple @ PostConstruct annotations in the same application and multiple @ PostConstruct annotations in the same Bean.
@Slf4j
@Component
public class InitBeanDemo {
@Autowired
private Environment env;
@PostConstruct
public void init() {
log.info("@PostConstruct DefaultProfiles: {}", Arrays.asList(env.getDefaultProfiles()));
log.info("@PostConstruct ActiveProfiles: {}", Arrays.asList(env.getActiveProfiles()));
}
Implement InitializingBean interface
Realize InitializingBean interface, in afterPropertiesSet () method to write the need to initialize the logic.
There can be multiple classes implementing the InitializingBean interface in the same application, which are sorted in the natural order of class names when executed.
@Slf4j
@Component
public class InitBeanDemo implements InitializingBean {
@Autowired
private Environment env;
@Override
public void afterPropertiesSet() throws Exception {
log.info("InitializingBean DefaultProfiles: {}", Arrays.asList(env.getDefaultProfiles()));
log.info("InitializingBean ActiveProfiles: {}", Arrays.asList(env.getActiveProfiles()));
}
}
Specify the initMethod method of Bean
The initMethod attribute using the @ Bean annotation can be used for methods executed after initialization of Bean. initMethod must be a parametric construction method of public void.
@Slf4j
public class InitBeanDemo implements InitializingBean {
@Autowired
private Environment env;
public void initMethod() {
log.info("initMethod DefaultProfiles: {}", Arrays.asList(env.getDefaultProfiles()));
log.info("initMethod ActiveProfiles: {}", Arrays.asList(env.getActiveProfiles()));
}
@Configuration
public class InitBeanConfig {
@Bean(initMethod="initMethod")
public InitBeanDemo initBeanDemo () {
return new InitBeanDemo();
}
}
Equivalent to the init-method attribute in the XML configuration:
<bean id="initBeanDemo" class="com.xxx.InitBeanDemo" init-method="initMethod"></bean>
4. Customize ApplicationListener Listening
There are two ways, one implements the interface and the other uses annotations.
Implement ApplicationListener interface
Listen for ContextRefreshedEvent events.
@Slf4j
@Component
public class InitBeanDemo implements ApplicationListener<ContextRefreshedEvent>{
@Autowired
private Environment env;
@Override
public void onApplicationEvent(ContextRefreshedEvent event) {
log.info("ApplicationListener DefaultProfiles: {}", Arrays.asList(env.getDefaultProfiles()));
log.info("ApplicationListener ActiveProfiles: {}", Arrays.asList(env.getActiveProfiles()));
}
}
@ EventListener annotation
The ContextRefreshedEvent event is specified in the method parameter.
@Slf4j
@Component
public class InitBeanDemo {
@Autowired
private Environment env;
@EventListener
public void onApplicationEvent2(ContextRefreshedEvent event) {
log.info("@EventListener DefaultProfiles: {}", Arrays.asList(env.getDefaultProfiles()));
log.info("@EventListener ActiveProfiles: {}", Arrays.asList(env.getActiveProfiles()));
}
}
5. Initialization interface provided by Spring Boot
ApplicationRunner interface
@Slf4j
@Component
public class InitBeanDemo implements ApplicationRunner {
@Autowired
private Environment env;
@Override
public void run(ApplicationArguments args) throws Exception {
log.info("ApplicationRunner: {}", args);
log.info("ApplicationRunner: {}", args.getOptionNames());
log.info("ApplicationRunner DefaultProfiles: {}", Arrays.asList(env.getDefaultProfiles()));
log.info("ApplicationRunner ActiveProfiles: {}", Arrays.asList(env.getActiveProfiles()));
}
}
CommandLineRunner interface
Multiple CommandLineRunner bean can be defined in the same application context and can be sorted using the @ Ordered interface or the @ Order annotation.
@Component
public class InitBeanDemo {
private final Environment env;
@Autowired
public InitBeanDemo (Environment environment) {
this.env = environment;
log.info("Constructor DefaultProfiles: {}", Arrays.asList(env.getDefaultProfiles()));
log.info("Constructor ActiveProfiles: {}", Arrays.asList(env.getActiveProfiles()));
}
}
Use the execution sequence of the above initialization method in the same Bean
Log fragments run in the same Bean using the above initialization method:
2021-06-07 11:24:41|INFO |main|c.c.s.s.t.ConstructorInitDemo|Constructor DefaultProfiles: [default]
2021-06-07 11:24:41|INFO |main|c.c.s.s.t.ConstructorInitDemo|Constructor ActiveProfiles: [sit]
2021-06-07 11:24:42|INFO |main|c.c.s.s.test.InitBeanDemo|@PostConstruct DefaultProfiles: [default]
2021-06-07 11:24:42|INFO |main|c.c.s.s.test.InitBeanDemo|@PostConstruct ActiveProfiles: [sit]
2021-06-07 11:24:42|INFO |main|c.c.s.s.test.InitBeanDemo|InitializingBean DefaultProfiles: [default]
2021-06-07 11:24:42|INFO |main|c.c.s.s.test.InitBeanDemo|InitializingBean ActiveProfiles: [sit]
2021-06-07 11:24:42|INFO |main|c.c.s.s.test.InitBeanDemo|initMethod DefaultProfiles: [default]
2021-06-07 11:24:42|INFO |main|c.c.s.s.test.InitBeanDemo|initMethod ActiveProfiles: [sit]
2021-06-07 11:24:44|INFO |main|c.c.s.s.test.InitBeanDemo|@EventListener DefaultProfiles: [default]
2021-06-07 11:24:44|INFO |main|c.c.s.s.test.InitBeanDemo|@EventListener ActiveProfiles: [sit]
2021-06-07 11:24:44|INFO |main|c.c.s.s.test.InitBeanDemo|ApplicationListener DefaultProfiles: [default]
2021-06-07 11:24:44|INFO |main|c.c.s.s.test.InitBeanDemo|ApplicationListener ActiveProfiles: [sit]
2021-06-07 11:24:44|INFO |main|c.c.s.s.test.InitBeanDemo|ApplicationRunner: org.springframework.boot.DefaultApplicationArguments@68bef3df
2021-06-07 11:24:44|INFO |main|c.c.s.s.test.InitBeanDemo|ApplicationRunner: []
2021-06-07 11:24:44|INFO |main|c.c.s.s.test.InitBeanDemo|ApplicationRunner DefaultProfiles: [default]
2021-06-07 11:24:44|INFO |main|c.c.s.s.test.InitBeanDemo|ApplicationRunner ActiveProfiles: [sit]
2021-06-07 11:24:44|INFO |main|c.c.s.s.test.InitBeanDemo|CommandLineRunner: {}
2021-06-07 11:24:44|INFO |main|c.c.s.s.test.InitBeanDemo|CommandLineRunner DefaultProfiles: [default]
2021-06-07 11:24:44|INFO |main|c.c.s.s.test.InitBeanDemo|CommandLineRunner ActiveProfiles: [sit]
That is, the order in which the whole article is sorted out.