Spring Autowired By type,name,constructor,Autowired and Qualifer 注解例子

Spring Framework的主要特性之一是DI[依赖注入],而实现该方式主要通过配置spring bean的

通常我们会在bean configuration file 中配置程序想要注入的bean 配置，也可以引用配置在其他 file中的bean[通过 ref 引用]。这种方法在需要注入很多bean的时候配置会显得比较繁锁

所以spring提供了 autowired 机制，从而必须定义每一个bean

目前有以下几种方式实现autowired:

autowired byName, 这种方式在 service 中必须实现需要inject的成员变量的setter方法,
并bean 中配置的bean name 必须和成员变量相同

1 2	<!-- autowiring byName, bean name should be same as the property name --> <bean name="employeeServiceByName" class="com.walterlife.springtest.service.EmployeeService" autowire="byName" />

autowired byType, 该种方式下同一种 bean type 只能配置一次

1
2

<!-- autowiring byType, there should be only one bean definition for the mapping -->
<bean name="employeeServiceByType" class="com.walterlife.springtest.service.EmployeeService" autowire="byType" />

autowired by constructor, 和 byType类似，只是该种方式是通过构造函数进行注入的

autowired by @Autowired 注解, 使用该种方式，需要配置

1 2	<!-- Enable Annotation based configuration --> <context:annotation-config />

@Qualifer, 该注解用来表明@Autowired的参数指定的类型，本身需要带上injected 的bean name

@Autowired(required=false)
public EmployeeAutowiredByConstructorService(@Qualifier("employee") Employee employee) {
    this.employee = employee;
}

下面举例说明以上几种autowired 方式

项目结构如下

SpringAutowired/
├── pom.xml
└── src
    └── main
        ├── java
        │   └── com
        │       └── walterlife
        │           └── springtest
        │               ├── App.java
        │               ├── model
        │               │   └── Employee.java
        │               └── service
        │                   ├── EmployeeAutowiredByConstructorService.java
        │                   ├── EmployeeAutowiredByTypeService.java
        │                   └── EmployeeService.java
        └── resources
            └── spring.xml
通过tree -L 8 -I "target|test" SpringAutowired  命令生成

maven 依赖如下,在pom.xml添加

<dependencies>
	<dependency>
		<groupId>junit</groupId>
		<artifactId>junit</artifactId>
		<version>4.11</version>
		<scope>test</scope>
	</dependency>
    <!-- Spring and Transactions -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>${spring-framework.version}</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-tx</artifactId>
        <version>${spring-framework.version}</version>
    </dependency>

    <!-- Logging with SLF4J & LogBack -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>${slf4j.version}</version>
        <scope>compile</scope>
    </dependency>
    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-classic</artifactId>
        <version>${logback.version}</version>
        <scope>runtime</scope>
    </dependency>
</dependencies>

添加 Model Bean Class,在bean configuration 中进行初始化

Employee.java
public class Employee {
    private String name;

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }
}

创建service class, 用于通过autowired 注入 bean

EmployeeService.java
public class EmployeeService {
    private Employee employee;

    public EmployeeService(Employee employee) {
        System.out.printf("%s\n", "Autowiring by constructer used!!!");
        this.employee = employee;
    }
    
    public EmployeeService() {
        System.out.printf("%s\n", "Default constructer invoked!!!");
    } 
    /**
     * @return the employee
     */
    public Employee getEmployee() {
        return employee;
    }

    /**
     * @param employee the employee to set
     */
    // 类中包含该函数，可以使用Autowired byName
    public void setEmployee(Employee employee) {
        this.employee = employee;
    }
}

该 service 可以用于 autowired by type, name, constructor
byType, byName 是通过 setter 方法来注入的，而 byConstructor 是通过constructor 方法注入的

当使用 byType, byName是通过默认构造函数实例化对象的,所以代码中显式的定义了默认构造函数

@Autowired bean autowiring byType

package com.walterlife.springtest.service;

import org.springframework.beans.factory.annotation.Autowired;
import com.walterlife.springtest.model.Employee;

public class EmployeeAutowiredByTypeService {
    @Autowired
    private Employee employee;

    /**
     * @return the employee
     */
    public Employee getEmployee() {
        return employee;
    }

    /**
     * @param employee the employee to set
     */
    @Autowired
    public void setEmployee(Employee employee) {
        this.employee = employee;
    }
}

Spring Autowired By type,name,constructor,Autowired and Qualifer 注解例子

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