Spring 自動掃描與裝配
通常你可以在 xml 配置檔案中,宣告一個 bean 或者 component,然後 Spring 容器會檢查和註冊你的 bean 或 component。
實際上,Spring 支援自動掃描 bean 或 component,你可以不必再在 xml 檔案中繁瑣的宣告 bean,Spring 會自動掃描並檢查你指定包的 bean 或 component。以下列舉一個簡單的 Spring Project,包含了 Controller、Service、DAO 層,由此分析下手動配置和自動掃描的不同。
首先建立一個新的 maven 工程 SpringAuto,開啟 Terminal,選擇 File->Open New Terminal,在終端中輸入:
mvn archetype:generate -DgroupId=com.shiyanlou.spring -DartifactId=SpringAuto -DarchetypeArtifactId=maven-archetype-quickstart
選擇 File->Open Workspace 切換工作空間,選擇 SpringAuto 目錄,必須切換到該目錄下,否則識別不了專案。
修改 pom.xml 檔案,新增 Spring 的依賴:
<?xml version = "1.0" encoding = "UTF-8"?> <project xmlns = "http://maven.apache.org/POM/4.0.0" xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation = "http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.shiyanlou.spring</groupId> <artifactId>SpringAuto</artifactId> <version>1.0-SNAPSHOT</version> <name>SpringAuto</name> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <maven.compiler.source>1.8</maven.compiler.source> <maven.compiler.target>1.8</maven.compiler.target> <spring.version>5.1.1.RELEASE</spring.version> </properties> <dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-core</artifactId> <version>${spring.version}</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>${spring.version}</version> </dependency> </dependencies> </project>
手動配置 component
先看一下正常手動配置一個 bean。
DAO 層,建立包 com.shiyanlou.spring.dao,建立 CustomerDAO.java。
內容如下:
package com.shiyanlou.spring.dao;
public class CustomerDAO {
@Override
public String toString(){
return "Hello , This is CustomerDAO";
}
}
Service 層,建立包 com.shiyanlou.spring.services,建立 CustomerService.java 內容如下:
package com.shiyanlou.spring.services;
import com.shiyanlou.spring.dao.CustomerDAO;
public class CustomerService {
CustomerDAO customerDAO;
public void setCustomerDAO(CustomerDAO customerDAO) {
this.customerDAO = customerDAO;
}
@Override
public String toString() {
return "CustomerService [customerDAO = " + customerDAO + "]";
}
}
在目錄 src/main/resources 建立並配置 SpringCustomer.xml 檔案:
<?xml version = "1.0" encoding = "UTF-8"?>
<beans xmlns = "http://www.springframework.org/schema/beans"
xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation = "http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id = "customerService" class = "com.shiyanlou.spring.services.CustomerService">
<property name = "customerDAO" ref = "customerDAO" />
</bean>
<bean id = "customerDAO" class = "com.shiyanlou.spring.dao.CustomerDAO" />
</beans>
最後,建立 App.java 檔案,在包路徑 com.shiyanlou.spring.common 下。內容如下:
package com.shiyanlou.spring.common;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.shiyanlou.spring.services.CustomerService;
public class App {
public static void main( String[] args ) {
ApplicationContext context =
new ClassPathXmlApplicationContext(new String[] {"SpringCustomer.xml"});
CustomerService cust = (CustomerService)context.getBean("customerService");
System.out.println(cust);
}
}
執行
mvn compile
mvn exec:java -Dexec.mainClass="com.shiyanlou.spring.common.App"
實驗結果如下:
自動掃描元件
用註釋 @Component 來表示這個 Class 是一個自動掃描元件。CustomerDAO.java 的內容如下:
package com.shiyanlou.spring.dao;
import org.springframework.stereotype.Component;
@Component
public class CustomerDAO
{
@Override
public String toString() {
return "Hello , This is CustomerDAO";
}
}
CustomerService.java 的內容如下:
package com.shiyanlou.spring.services;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import com.shiyanlou.spring.dao.CustomerDAO;
@Component
public class CustomerService
{
@Autowired
CustomerDAO customerDAO;
@Override
public String toString() {
return "CustomerService [customerDAO=" + customerDAO + "]";
}
}
配置檔案 SpringCustomer.xml 如下
<?xml version = "1.0" encoding = "UTF-8"?>
<beans xmlns = "http://www.springframework.org/schema/beans"
xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
xmlns:context = "http://www.springframework.org/schema/context"
xsi:schemaLocation = "
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<context:component-scan base-package = "com.shiyanlou.spring"/>
</beans>
注意:以上 xml 檔案中,加入了 context:component-scan 標籤,beans 中也加入了標籤,這樣就將 Spring 的自動掃描特性引入,base-package 表示元件的存放位置,Spring 將掃描對應資料夾下的 bean(用 @Component 註釋過的),將這些 bean 註冊到容器中。
最後執行結果與手動配置的結果一致。
自定義掃描元件名稱
上例中,預設情況下,Spring 將把元件 Class 的第一個字母變成小寫,來作為自動掃描元件的名稱,例如將 CustomerService 轉變為 customerService,你可以用 customerService 這個名字呼叫元件,如下:
CustomerService cust = (CustomerService)context.getBean("customerService");
也可以像下面這樣,建立自定義的元件名稱:
@Service("AAA")
public class CustomerService
...
但是得新增下面的程式碼:
import org.springframework.stereotype.Service;
可以呼叫自己定義的元件了,如下:
CustomerService cust = (CustomerService)context.getBean("AAA");
自動掃描元件的註釋型別
有 4 種註釋型別,分別是:
1、@Component —— 表示一個自動掃描 component。
2、@Repository —— 表示持久化層的 DAO component。
3、@Service —— 表示業務邏輯層的 Service component。
4、@Controller —— 表示表示層的 Controller component。
在專案中,我們可以將所有自動掃描元件都用 @Component 註釋,Spring 將會掃描所有用 @Component 註釋過得元件。實際上,@Repository 、@Service 、@Controller 三種註釋是為了加強程式碼的閱讀性而創造的,可以在不同的應用層中,用不同的註釋,我們可以在上一個專案的基礎上改一下注釋,如下:
DAO 層:
package com.shiyanlou.spring.dao;
import org.springframework.stereotype.Repository;
@Repository
public class CustomerDAO
{
@Override
public String toString() {
return "Hello , This is CustomerDAO";
}
}
Service 層:
package com.shiyanlou.spring.services;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.shiyanlou.spring.dao.CustomerDAO;
@Service
public class CustomerService
{
@Autowired
CustomerDAO customerDAO;
@Override
public String toString() {
return "CustomerService [customerDAO=" + customerDAO + "]";
}
}
自動掃描中過濾元件
1). Filter Component - include
下例演示了用 “filter” 自動掃描註冊元件,這些元件只要匹配定義的 “regex” 的命名規則,Class 前就不需要用 @Component 進行註釋。
DAO 層,CustomerDAO.java 如下:
package com.shiyanlou.spring.dao;
public class CustomerDAO
{
@Override
public String toString() {
return "Hello , This is CustomerDAO";
}
}
Service 層,CustomerService.java 如下:
package com.shiyanlou.spring.services;
import org.springframework.beans.factory.annotation.Autowired;
import com.shiyanlou.spring.dao.CustomerDAO;
public class CustomerService
{
@Autowired
CustomerDAO customerDAO;
@Override
public String toString() {
return "CustomerService [customerDAO=" + customerDAO + "]";
}
}
SpringFiltering.xml 配置如下:
<beans xmlns = "http://www.springframework.org/schema/beans"
xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
xmlns:context = "http://www.springframework.org/schema/context"
xsi:schemaLocation = "
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<context:component-scan base-package = "com.shiyanlou.spring" >
<context:include-filter type = "regex"
expression = "com.shiyanlou.spring.dao.*DAO.*" />
<context:include-filter type = "regex"
expression = "com.shiyanlou.spring.services.*Service.*" />
</context:component-scan>
</beans>
以上 xml 檔案中,所有檔名字,只要包含 DAO 和 Service( DAO._,_Service. )關鍵字的,都將被檢查註冊到 Spring 容器中。
建立 App.java 並執行如下:
package com.shiyanlou.spring.common;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.lei.customer.services.CustomerService;
public class App
{
public static void main( String[] args )
{
ApplicationContext context =
new ClassPathXmlApplicationContext(new String[] {"SpringFiltering.xml"});
CustomerService cust = (CustomerService)context.getBean("customerService");
System.out.println(cust);
}
}
執行結果與之前相同。
2). Filter Component——exclude
也可以用 exclude,制定元件避免被 Spring 發現並被註冊到容器中。以下配置排除用 @Service 註釋過的元件:
<context:component-scan base-package = "com.shiyanlou.spring" >
<context:exclude-filter type = "annotation"
expression = "org.springframework.stereotype.Service" />
</context:component-scan>
以下配置排除包含 DAO 關鍵字的元件:
<context:component-scan base-package = "com.shiyanlou.spring" >
<context:exclude-filter type = "regex"
expression = "com.shiyanlou.spring.dao.*DAO.*" />
</context:component-scan>
excludeFilters 是指明哪些類不被掃描到
相應地
includeFilters 是指明只掃描哪些類