Spring Setter依赖注入示例

学习如何编写Spring Setter依赖注入示例 。 Setter注入是Spring依赖注入的一种 。 Spring支持字段注入，Setter注入以及构造函数注入，以将依赖项注入Spring托管的bean中。本教程的范围仅限于Setter注入。

有关Spring依赖注入的更多信息：

Spring构造函数依赖注入示例
Spring字段依赖注入示例
Spring依赖注入–字段vs设置器vs构造函数注入
Spring依赖注入和控制反转

考虑一下，我们有一个DogsService ，它是一个基于Spring的REST服务。

我们将编写一个DogsController ， DogsService和DogsDao 。这是一个不执行任何操作的虚拟服务。这里的目的是了解Spring Dependency Injection如何与Setter方法一起使用。

不知道如何编写Spring Boot Rest Service？

阅读： Spring Boot Rest Service

想更多地了解Spring Framework？

读这个：

Spring框架介绍
Spring框架架构
Spring依赖注入和控制反转
Spring靴休息服务

DogsDao.java

没有字段，因此没有依赖性。我们添加了带有打印消息的无参数构造函数。

package com.amitph.spring.dogs.dao;import com.amitph.spring.dogs.repo.Dog;
import org.springframework.stereotype.Component;import java.util.List;@Component
public class DogsDao {public DogsDao(){System.out.println("DogsDao no-arg constructor called");}public List<Dog> getAllDogs() {System.out.println("DogsDao.getAllDogs called");return null;}
}

DogsService.java

DogsService取决于DogsDao 。在下面的类中， setter方法用@Autowired注释。为了查看Setter注入的工作方式，我们在setter方法中添加了一条print语句。除了使用setter方法外，我们还添加了无参数构造函数和带有相应打印消息的参数化构造函数 。

package com.amitph.spring.dogs.service;import com.amitph.spring.dogs.dao.DogsDao;
import com.amitph.spring.dogs.repo.Dog;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;import java.util.List;@Component
public class DogsService {private DogsDao dao;public List<Dog> getDogs() {System.out.println("DogsService.getDogs called");return dao.getAllDogs();}@Autowiredpublic void setDao(DogsDao dao) {System.out.println("DogsService setter called");this.dao = dao;}public DogsService(){System.out.println("DogsService no-arg constructor called");}public DogsService(DogsDao dao) {System.out.println("DogsService arg constructor called");this.dao = dao;}
}

DogsController.java

DogsController依赖于DogsService 。 设置器带有@Autowired注释，并具有打印语句。除了setter方法外，我们还添加了无参数和参数化构造函数以及相应的打印消息。

package com.amitph.spring.dogs.web;import com.amitph.spring.dogs.repo.Dog;
import com.amitph.spring.dogs.service.DogsService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;import java.util.List;@RestController
@RequestMapping("/dogs")
public class DogsController {private DogsService service;@GetMappingpublic List<Dog> getDogs() {return service.getDogs();}@Autowiredpublic void setService(DogsService service) {System.out.println("DogsController setter called");this.service = service;}
}

应用启动

.   ____          _            __ _ _/\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \\\/  ___)| |_)| | | | | || (_| |  ) ) ) )'  |____| .__|_| |_|_| |_\__, | / / / /=========|_|==============|___/=/_/_/_/:: Spring Boot ::        (v2.1.0.RELEASE)2019-02-04 19:06:17.058  INFO 68545 --- [           main] com.amitph.spring.dogs.Application       : Starting Application on Amitsofficemac.gateway with PID 68545 (/Users/aphaltankar/Workspace/personal/dog-service-jpa/out/production/classes started by aphaltankar in /Users/aphaltankar/Workspace/personal/dog-service-jpa)
2019-02-04 19:06:17.061  INFO 68545 --- [           main] com.amitph.spring.dogs.Application       : No active profile set, falling back to default profiles: default
2019-02-04 19:06:17.670  INFO 68545 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data repositories in DEFAULT mode.
2019-02-04 19:06:17.724  INFO 68545 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 48ms. Found 1 repository interfaces.
2019-02-04 19:06:17.992  INFO 68545 --- [           main] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration' of type [org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration$$EnhancerBySpringCGLIB$$4a5366ed] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
2019-02-04 19:06:18.225  INFO 68545 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2019-02-04 19:06:18.237  INFO 68545 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2019-02-04 19:06:18.237  INFO 68545 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/9.0.12
2019-02-04 19:06:18.242  INFO 68545 --- [           main] o.a.catalina.core.AprLifecycleListener   : The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: [/Users/aphaltankar/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.]
2019-02-04 19:06:18.315  INFO 68545 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2019-02-04 19:06:18.315  INFO 68545 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1205 ms
2019-02-04 19:06:18.339  INFO 68545 --- [           main] o.s.b.w.servlet.ServletRegistrationBean  : Servlet dispatcherServlet mapped to [/]
2019-02-04 19:06:18.342  INFO 68545 --- [           main] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2019-02-04 19:06:18.342  INFO 68545 --- [           main] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2019-02-04 19:06:18.342  INFO 68545 --- [           main] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'formContentFilter' to: [/*]
2019-02-04 19:06:18.342  INFO 68545 --- [           main] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2019-02-04 19:06:18.434  INFO 68545 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
2019-02-04 19:06:18.524  INFO 68545 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
2019-02-04 19:06:18.645  INFO 68545 --- [           main] o.hibernate.jpa.internal.util.LogHelper  : HHH000204: Processing PersistenceUnitInfo [name: default...]
2019-02-04 19:06:18.690  INFO 68545 --- [           main] org.hibernate.Version                    : HHH000412: Hibernate Core {5.3.7.Final}
2019-02-04 19:06:18.691  INFO 68545 --- [           main] org.hibernate.cfg.Environment            : HHH000206: hibernate.properties not found
2019-02-04 19:06:18.779  INFO 68545 --- [           main] o.hibernate.annotations.common.Version   : HCANN000001: Hibernate Commons Annotations {5.0.4.Final}
2019-02-04 19:06:18.868  INFO 68545 --- [           main] org.hibernate.dialect.Dialect            : HHH000400: Using dialect: org.hibernate.dialect.MySQL5InnoDBDialect
2019-02-04 19:06:19.279  INFO 68545 --- [           main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
DogsDao no-arg constructor called
DogsService no-arg constructor called
DogsService setter called
DogsController no-arg constructor called
DogsController setter called
2019-02-04 19:06:19.650  INFO 68545 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2019-02-04 19:06:19.681  WARN 68545 --- [           main] aWebConfiguration$JpaWebMvcConfiguration : spring.jpa.open-in-view is enabled by default. Therefore, database queries may be performed during view rendering. Explicitly configure spring.jpa.open-in-view to disable this warning
2019-02-04 19:06:19.856  INFO 68545 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2019-02-04 19:06:19.859  INFO 68545 --- [           main] com.amitph.spring.dogs.Application       : Started Application in 3.138 seconds (JVM running for 3.647)

春天发生的事情是Spring首先尝试实例化DogsController并发现了对DogsService的依赖。因此，它实例化了DogsService ，而后者又依赖于DogsDao 。因此， DogsDao是第一个实例化的，然后是DogsService ，最后是DogsController 。

让我们详细看看发生了什么。