Spring字段依赖注入示例

学习如何编写Spring Field Injection示例 。 字段注入是Spring框架 依赖注入的一种 。在本教程中，我们将编写几个类，并看一看现场注入工程。

有关Spring依赖注入的更多信息：

Spring Setter依赖注入示例
Spring构造函数依赖注入示例
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

基于字段的依赖注入

在这种类型的依赖关系注入中，Spring将依赖关系直接分配给字段。它不同于构造函数注入或基于Setter的依赖注入。

有趣的是，即使字段是私有的，Spring也会注入依赖项。 Spring使用Java Reflections来做到这一点。因此，许多专家称它为不安全。

字段注入可能是依赖注入的最简单（但有风险）形式。为了更好地理解它，我们假设我们有一个正在运行的Spring Boot Service 。它是一项虚拟服务，旨在了解现场注入。

不知道如何编写Spring Boot Rest Service？
读这个： Spring靴休息服务

想更多地了解Spring Framework？
读这个：

Spring框架介绍
Spring建筑
春天@Autowired
Spring中的@Autowired注释

首先让我们编写DogsService类

狗服务

此类对DogsDao具有依赖关系。用@Autowired注释参考变量。有一个setter和两个构造函数 ，分别带有打印消息。

 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 { @Autowired private DogsDao dao; public List<Dog> getDogs() { System.out.println( "DogsService.getDogs called" ); return dao.getAllDogs(); } public 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; }  }

狗的控制器

控制器对DogsService具有依赖性。与服务类类似，将@Autowired批注添加到参考变量。有带有打印消息的setter和构造函数。

 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 { @Autowired private DogsService service; @GetMapping public List<Dog> getDogs() { return service.getDogs(); } public void setService(DogsService service) { System.out.println( "DogsController setter called" ); this .service = service; } public DogsController(){ System.out.println( "DogsController no-arg constructor called" ); } public DogsController(DogsService service) { System.out.println( "DogsController arg constructor called" ); this .service = service; }  }

运行代码

 .  ____         _           __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \  ( ( )\___ | '_ | ' _| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot ::       (v2. 1.0 .RELEASE)  2019 - 02 - 05 06 : 34 : 14.956 INFO 69421 --- [          main] com.amitph.spring.dogs.Application      : Starting Application on Amits-office-mac.local with PID 69421 (/Users/aphaltankar/Workspace/personal/dog-service-jpa/out/production/classes started by aphaltankar in /Users/aphaltankar/Workspace/personal/dog-service-jpa)  2019 - 02 - 05 06 : 34 : 14.957 INFO 69421 --- [          main] com.amitph.spring.dogs.Application      : No active profile set, falling back to default profiles: default  2019 - 02 - 05 06 : 34 : 15.655 INFO 69421 --- [          main] .sdrcRepositoryConfigurationDelegate : Bootstrapping Spring Data repositories in DEFAULT mode.  2019 - 02 - 05 06 : 34 : 15.711 INFO 69421 --- [          main] .sdrcRepositoryConfigurationDelegate : Finished Spring Data repository scanning in 50ms. Found --- [          main] .sdrcRepositoryConfigurationDelegate : Finished Spring Data repository scanning in 50ms. Found 1 repository interfaces.  2019 - 02 - 05 06 : 34 : 16.013 INFO 69421 --- [          main] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration' of type [org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration$EnhancerBySpringCGLIB$1cc57cd7] is not eligible for getting processed by all BeanPostProcessors ( for example: not eligible for auto-proxying)  2019 - 02 - 05 06 : 34 : 16.318 INFO 69421 --- [          main] osbwembedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)  2019 - 02 - 05 06 : 34 : 16.335 INFO 69421 --- [          main] o.apache.catalina.core.StandardService  : Starting service [Tomcat]  2019 - 02 - 05 06 : 34 : 16.335 INFO 69421 --- [          main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/ 9.0 . 12  2019 - 02 - 05 06 : 34 : 16.342 INFO 69421 --- [          main] oacatalina.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 - 05 06 : 34 : 16.429 INFO 69421 --- [          main] oaccC[Tomcat].[localhost].[/]      : Initializing Spring embedded WebApplicationContext  2019 - 02 - 05 06 : 34 : 16.429 INFO 69421 --- [          main] osweb.context.ContextLoader           : Root WebApplicationContext: initialization completed in 1419 ms  2019 - 02 - 05 06 : 34 : 16.454 INFO 69421 --- [          main] osbwservlet.ServletRegistrationBean : Servlet dispatcherServlet mapped to [/]  2019 - 02 - 05 06 : 34 : 16.457 INFO 69421 --- [          main] osbwservlet.FilterRegistrationBean  : Mapping filter: 'characterEncodingFilter' to: [/*]  2019 - 02 - 05 06 : 34 : 16.458 INFO 69421 --- [          main] osbwservlet.FilterRegistrationBean  : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]  2019 - 02 - 05 06 : 34 : 16.458 INFO 69421 --- [          main] osbwservlet.FilterRegistrationBean  : Mapping filter: 'formContentFilter' to: [/*]  2019 - 02 - 05 06 : 34 : 16.458 INFO 69421 --- [          main] osbwservlet.FilterRegistrationBean  : Mapping filter: 'requestContextFilter' to: [/*]  2019 - 02 - 05 06 : 34 : 16.581 INFO 69421 --- [          main] com.zaxxer.hikari.HikariDataSource      : HikariPool- 1 - Starting...  2019 - 02 - 05 06 : 34 : 16.702 INFO 69421 --- [          main] com.zaxxer.hikari.HikariDataSource      : HikariPool- 1 - Start completed.  2019 - 02 - 05 06 : 34 : 16.830 INFO 69421 --- [          main] o.hibernate.jpa.internal.util.LogHelper : HHH000204: Processing PersistenceUnitInfo [ name: default ...]  2019 - 02 - 05 06 : 34 : 16.906 INFO 69421 --- [          main] org.hibernate.Version                   : HHH000412: Hibernate Core { 5.3 . 7 .Final}  2019 - 02 - 05 06 : 34 : 16.907 INFO 69421 --- [          main] org.hibernate.cfg.Environment           : HHH000206: hibernate.properties not found  2019 - 02 - 05 06 : 34 : 17.059 INFO 69421 --- [          main] o.hibernate.annotations.common.Version  : HCANN000001: Hibernate Commons Annotations { 5.0 . 4 .Final}  2019 - 02 - 05 06 : 34 : 17.188 INFO 69421 --- [          main] org.hibernate.dialect.Dialect           : HHH000400: Using dialect: org.hibernate.dialect.MySQL5InnoDBDialect  2019 - 02 - 05 06 : 34 : 17.783 INFO 69421 --- [          main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'  DogsDao no-arg constructor called  DogsService no-arg constructor called  DogsController no-arg constructor called  2019 - 02 - 05 06 : 34 : 18.208 INFO 69421 --- [          main] ossconcurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor'  2019 - 02 - 05 06 : 34 : 18.244 WARN 69421 --- [          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 . Therefore, database queries may be performed during view rendering. Explicitly configure spring.jpa.open-in-view to disable . Therefore, database queries may be performed during view rendering. Explicitly configure spring.jpa.open-in-view to disable this warning  2019 - 02 - 05 06 : 34 : 18.420 INFO 69421 --- [          main] osbwembedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''  2019 - 02 - 05 06 : 34 : 18.422 INFO 69421 --- [          main] com.amitph.spring.dogs.Application      : Started Application in 3.878 seconds (JVM running for 4.57 )

所有三个无参数的控制器按顺序调用。没有调用setter或参数化的构造函数 。需要注意的另一件事是这些字段，这些字段被标记为@Autowired是private 。

春天可以设置

Spring使用反射在对象上设置私有字段。这听起来很有用，但另一方面，它也不安全。现场注射，其安全性和实用性一直备受争议。 Spring不遵守对象访问规则。现在，有些人可能会支持这种说法，或者说spring IoC容器管理所有对象，应该获得对这些对象的最高控制权。

 @Component  public class MyClass { @Autowired private DogsController controller; @Autowired private DogsService service; @Autowired private DogsDao dao; @Autowired private ApplicationProperties properties;  / business methods  }

作为开发人员，我一直喜欢使用Field Injection，因为它真的很简单并且可读性更高。您实际上可以避免编写setter方法或构造函数，而将精力放在业务方法上。

摘要

您了解了Field Injection是Spring Dependency Injection的一种 ，并编写了几类来查看它的工作原理。字段注入很简单，使类更具可读性。但是，出于安全考虑，许多人讨厌它并避免使用它。

在接下来的部分中，我们将看到Setter注入 ， Field注入 和 Constructor注入 这三种方法之间的详细区别。

快乐编码！

翻译自: https://www.javacodegeeks.com/2019/02/spring-field-dependency-injection-example.html