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spring(四)：spring中给bean的属性赋值

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11/30
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spring中给bean的属性赋值

  • xml文件properties标签设置 
    <bean id="student" class="com.enjoy.study.cap10.Student" >
    
        <property name="id" value="18"/>
    
        <property name="name" value="wxf"/>
    
</bean>
  • 注解
    • @Autowired
    • @Value
    • @Resource　　JSR250
    • @Inject　　　　JSR330

本章博客重点介绍注解赋值的使用

@Autowired

自动装配：Spring利用依赖注入完成对IOC容器中各个组件的依赖关系赋值 

@Target({ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD, ElementType.ANNOTATION_TYPE})

可以在构造方法、方法、参数、属性以及注解上使用，最常用的就是在属性上使用

不管使在什么地方使用，都是从IOC容器中获取bean

基本使用 

@Configuration

@ComponentScan("com.enjoy.study.cap11")

public class CapMainConfig {

}
@Repository

public class TestDao {

    public void test(){

        System.out.println("---------TestDao test()--------");

    }

}

@Service

public class TestService {

    @Autowired

    private TestDao testDao;

    public void test() {

        System.out.println("---------TestService test()--------"+testDao);

    }

    public TestDao getTestDao() {

        return testDao;

    }

    public void setTestDao(TestDao testDao) {

        this.testDao = testDao;

    }

}
测试

public class TestCap {

    @Test

    public void testMethod(){

        ApplicationContext context = new AnnotationConfigApplicationContext(CapMainConfig.class);

        TestDao testDao = (TestDao) context.getBean("testDao");

        TestService service = (TestService) context.getBean("testService");

        TestDao testDao1 = service.getTestDao();

        System.out.println(testDao==testDao1);

    }

}
结果

true

结论：

  • @Autowired注解先按照类型去IOC容器中找到相应组件，再将id为testDao的bean取出并注入TestService的testDao属性中
  • 如果没有找到该id对应的bean，就将相同类型的bean注入，不会报错

优先级

当容器中有多个相同类型的bean，使用@Autowired注解注入哪一个？ 

@Configuration

@ComponentScan("com.enjoy.study.cap11")

public class CapMainConfig {

    @Bean("testDao2")

    public TestDao testDao(){

        TestDao testDao = new TestDao();

        testDao.setFlag(2);

        return testDao;

    }

}
@Repository

public class TestDao {

    private int flag = 1;

    public int getFlag() {

        return flag;

    }

    public void setFlag(int flag) {

        this.flag = flag;

    }

    @Override

    public String toString() {

        return "TestDao{" +

                "flag=" + flag +

                '}';

    }

}

@Service

public class TestService {

    @Autowired

    private TestDao testDao2;

    public TestDao getTestDao() {

        return testDao2;

    }

    public void setTestDao(TestDao testDao) {

        this.testDao2 = testDao;

    }

}
测试类

public class TestCap {

    @Test

    public void testMethod(){

        ApplicationContext context = new AnnotationConfigApplicationContext(CapMainConfig.class);

        TestService service = context.getBean(TestService.class);

        TestDao testDao1 = service.getTestDao();

        System.out.println(testDao1);

    }

}
结果

TestDao{flag=2}

结论：

TestService中注入的是testDao2；另外，如果TestService中定义private TestDao testDao；那么结果是TestDao{flag=1}，也就是TestService中注入的是testDao

指定注入哪个bean

如果TestService中定义private TestDao testDao；还是想要注入testDao，那么可以使用@Qualifier+@Autowired 

@Service

public class TestService {

    @Qualifier("testDao")

    @Autowired

    private TestDao testDao2;

    public TestDao getTestDao() {

        return testDao2;

    }

    public void setTestDao(TestDao testDao) {

        this.testDao2 = testDao;

    }

}
结果

TestDao{flag=1}

required属性

当容器中不存在该类型的bean时：

将配置类中的@Bean和TestDao类的@Repository注释掉 

@Configuration

@ComponentScan("com.enjoy.study.cap11")

public class CapMainConfig {

    //@Bean("testDao")

    public TestDao testDao(){

        TestDao testDao = new TestDao();

        testDao.setFlag(2);

        return testDao;

    }

}
//@Repository

public class TestDao {

    private int flag = 1;

    public int getFlag() {

        return flag;

    }

    public void setFlag(int flag) {

        this.flag = flag;

    }

    @Override

    public String toString() {

        return "TestDao{" +

                "flag=" + flag +

                '}';

    }

}

@Service

public class TestService {

    @Autowired

    private TestDao testDao2;

    public TestDao getTestDao() {

        return testDao2;

    }

    public void setTestDao(TestDao testDao) {

        this.testDao2 = testDao;

    }

}
public class TestCap {

    @Test

    public void testMethod(){

        ApplicationContext context = new AnnotationConfigApplicationContext(CapMainConfig.class);

        TestService service = context.getBean(TestService.class);

        TestDao testDao1 = service.getTestDao();

        System.out.println(testDao1);

    }

}
结果

org.springframework.beans.factory.NoSuchBeanDefinitionException:

	No qualifying bean of type 'com.enjoy.study.cap11.dao.TestDao' available:

		expected at least 1 bean which qualifies as autowire candidate.

			Dependency annotations:

				{@org.springframework.beans.factory.annotation.Autowired(required=true)}

结论：

启动容器，两个TestDao类型的bean都不会被加载，并且提示异常报错；原因是@Autowired注解的required属性默认为true，即要求容器中必须存在bean，否则抛出异常

使用@Autowired(required=false)即可解决 

@Service

public class TestService {

    @Autowired(required = false)

    private TestDao testDao2;

    public TestDao getTestDao() {

        return testDao2;

    }

    public void setTestDao(TestDao testDao) {

        this.testDao2 = testDao;

    }

}
结果

null

结论：

因为容器中没有TestDao类型的bean，所以打印结果为null

验证@Qualifier和@Primary加载顺序

@Primary的作用是使得该bean默认优先被使用

应用场景：多个类都需要注入一个bean时，如果每个类都使用@Qualifier指定注入相同的bean会导致代码冗余，这时可以使用@Primary直接在该bean上作用即可 

@Configuration

@ComponentScan("com.enjoy.study.cap11")

public class CapMainConfig {

    @Primary

    @Bean("testDao2")

    public TestDao testDao(){

        TestDao testDao = new TestDao();

        testDao.setFlag(2);

        return testDao;

    }

}
@Repository

public class TestDao {

    private int flag = 1;

    public int getFlag() {

        return flag;

    }

    public void setFlag(int flag) {

        this.flag = flag;

    }

    @Override

    public String toString() {

        return "TestDao{" +

                "flag=" + flag +

                '}';

    }

}

@Service

public class TestService {

    @Qualifier("testDao")

    @Autowired(required = false)

    private TestDao testDao2;

    public TestDao getTestDao() {

        return testDao2;

    }

    public void setTestDao(TestDao testDao) {

        this.testDao2 = testDao;

    }

}
public class TestCap {

    @Test

    public void testMethod(){

        ApplicationContext context = new AnnotationConfigApplicationContext(CapMainConfig.class);

        TestDao testDao = context.getBean(TestDao.class);

        System.out.println("context.getBean(TestDao.class) = " + testDao);

        TestService service = context.getBean(TestService.class);

        TestDao testDao1 = service.getTestDao();

        System.out.println("service.getTestDao() = " + testDao1);

    }

}
结果

context.getBean(TestDao.class) = TestDao{flag=2}

service.getTestDao() = TestDao{flag=1}

结论1：

  • TestService中注入的是testDao，直接从容器中获取时取到的是testDao2
  • 说明@Qualifier是根据bean的id获取的bean，不受@Primary影响

修改TestService类 

@Service

public class TestService {

//    @Qualifier("testDao")

    @Autowired(required = false)

    private TestDao testDao;

    public TestDao getTestDao() {

        return testDao;

    }

    public void setTestDao(TestDao testDao) {

        this.testDao = testDao;

    }

}

结果

context.getBean(TestDao.class) = TestDao{flag=2}

service.getTestDao() = TestDao{flag=2}

结论2：

  • 注入的都是@Primary指定的testDao2
  • 通过@Primary标记的bean，默认首先被使用

@Value 
@Configuration

public class CapMainConfig {

    @Bean

    public Student student(){

        return new Student();

    }

}
public class TestCap {

    @Test

    public void testMethod(){

        ApplicationContext context = new AnnotationConfigApplicationContext(CapMainConfig.class);

        Student student = (Student) context.getBean("student");

        System.out.println("student = " + student);

    }

}

字符形式@Value("") 

public class Student {

    @Value("12")

    private Integer id;

    @Value("wxf")

    private String name;

    @Override

    public String toString() {

        return "Student{" +

                "id=" + id +

                ", name='" + name + '\'' +

                '}';

    }

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

}

结果 

student = Student{id=12, name='wxf'}

@Value("#{}")

@Value("#{}") 表示SpEl表达式，通常用来获取bean的属性，或者调用bean的某个方法

容器中bean类： 

public class TestBean {

    @Value("qf")

    private String name;

    @Value("12")

    private Integer id;

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

}
public class Student {

    @Autowired

    private TestBean testBean;

    //表达式，或者字符形式#{1}

    @Value("#{12-1}")

    private String sex;

    //bean属性

    @Value("#{testBean.id}")

    private Integer id;

    //bean方法

    @Value("#{testBean.getName()}")

    private String name;

    public String getSex() {

        return sex;

    }

    public void setSex(String sex) {

        this.sex = sex;

    }

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    @Override

    public String toString() {

        return "Student{" +

                "sex='" + sex + '\'' +

                ", id=" + id +

                ", name='" + name + '\'' +

                '}';

    }

}
配置类
@Configuration

public class CapMainConfig {

    @Bean

    public TestBean testBean(){

        return new TestBean();

    }

    @Bean

    public Student student(){

        return new Student();

    }

}
测试类
public class TestCap {

    @Test

    public void testMethod(){

        ApplicationContext context = new AnnotationConfigApplicationContext(CapMainConfig.class);

        Student student = (Student) context.getBean("student");

        System.out.println("student = " + student);

    }

}
结果
student = Student{sex='11', id=12, name='qf'}

@Value("${}")

通过@Value("${}") 可以获取对应属性文件中定义的属性值

想要使用${}方式获取值

首先通过@PropertySource注解将properties配置文件中的值存储到Spring的 Environment中 ，Environment接口提供方法去读取配置文件中的值，参数是properties文件中定义的key值 

@Configuration

@PropertySource(value={"classpath:test.properties","classpath:test2.properties"})

public class MainConfig {

    @Bean

    public Person person(){

        return new Person();

    }

}

测试 

配置文件

test.properties文件

TestStr=12345

test2.properties文件

TestStr1=123456789
bean类

public class Person {

    @Value("${TestStr}")

    private Integer id;

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

}
测试

public class TestCap {

    @Test

    public void testM(){

        ApplicationContext context = new AnnotationConfigApplicationContext(MainConfig.class);

        Person person = context.getBean(Person.class);

        System.out.println("person.getId() = " + person.getId());

    }

}
结果

person.getId() = 12345　

@Resource

基本使用 

@Configuration

@ComponentScan("com.enjoy.study.cap11")

public class CapMainConfig {

    @Primary

    @Bean("testDao2")

    public TestDao testDao(){

        TestDao testDao = new TestDao();

        testDao.setFlag(2);

        return testDao;

    }

}
@Repository

public class TestDao {

    private int flag = 1;

    public int getFlag() {

        return flag;

    }

    public void setFlag(int flag) {

        this.flag = flag;

    }

    @Override

    public String toString() {

        return "TestDao{" +

                "flag=" + flag +

                '}';

    }

}

@Service

public class TestService {

    @Resource

    private TestDao testDao;

    public TestDao getTestDao() {

        return testDao;

    }

    public void setTestDao(TestDao testDao) {

        this.testDao = testDao;

    }

}
public class TestCap {

    @Test

    public void testMethod(){

        ApplicationContext context = new AnnotationConfigApplicationContext(CapMainConfig.class);

        TestDao testDao = context.getBean(TestDao.class);

        System.out.println("context.getBean(TestDao.class) = " + testDao);

        TestService service = context.getBean(TestService.class);

        TestDao testDao1 = service.getTestDao();

        System.out.println("service.getTestDao() = " + testDao1);

    }

}
结果

context.getBean(TestDao.class) = TestDao{flag=2}

service.getTestDao() = TestDao{flag=1}

结论：

  • @Primary对@Resource并不生效
  • @Resource和@Autowired一样可以装配bean

name属性

可以指定注入哪个bean 

@Service

public class TestService {

    @Resource(name = "testDao2")

    private TestDao testDao;

    public TestDao getTestDao() {

        return testDao;

    }

    public void setTestDao(TestDao testDao) {

        this.testDao = testDao;

    }

}
结果

context.getBean(TestDao.class) = TestDao{flag=2}

service.getTestDao() = TestDao{flag=2}

bean为null的情况

将TestDao上的@Repository和配置类中的@Bean都注释掉，再测试会抛出异常 

org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'testDao2' available

所以@Resource并不支持类似@Autowired(required=false)的功能

@Inject

基本使用

需要导入javax.inject的包 

<dependency>

	<groupId>javax.inject</groupId>

	<artifactId>javax.inject</artifactId>

	<version>1</version>

</dependency>

测试 

@Configuration

@ComponentScan("com.enjoy.study.cap11")

public class CapMainConfig {

    @Primary

    @Bean("testDao2")

    public TestDao testDao(){

        TestDao testDao = new TestDao();

        testDao.setFlag(2);

        return testDao;

    }

}

@Repository

public class TestDao {

    private int flag = 1;

    public int getFlag() {

        return flag;

    }

    public void setFlag(int flag) {

        this.flag = flag;

    }

    @Override

    public String toString() {

        return "TestDao{" +

                "flag=" + flag +

                '}';

    }

}

@Service

public class TestService {

    @Inject

    private TestDao testDao;

    public TestDao getTestDao() {

        return testDao;

    }

    public void setTestDao(TestDao testDao) {

        this.testDao = testDao;

    }

}

public class TestCap {

    @Test

    public void testMethod(){

        ApplicationContext context = new AnnotationConfigApplicationContext(CapMainConfig.class);

        TestDao testDao = context.getBean(TestDao.class);

        System.out.println("context.getBean(TestDao.class) = " + testDao);

        TestService service = context.getBean(TestService.class);

        TestDao testDao1 = service.getTestDao();

        System.out.println("service.getTestDao() = " + testDao1);

    }

}

结果

context.getBean(TestDao.class) = TestDao{flag=2}

service.getTestDao() = TestDao{flag=2}

结论：

@Inject支持@Primary

bean为null的情况

将TestDao上的@Repository和配置类中的@Bean都注释掉，再测试会抛出异常 

org.springframework.beans.factory.NoSuchBeanDefinitionException

@Inject并不支持类似@Autowired(required=false)的功能

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