spring之ComponentScan注解分析

向右看齐 2023-01-21 14:18 52阅读 0赞

## 1：源码分析 ##

源码如下：

@Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    @Documented
    // 可多次定义，多次定义结果存储在注解ComponentScans
    @Repeatable(ComponentScans.class)
    public @interface ComponentScan { 
    
    	// basePackages别名，当只有basePackages需要定义时，可以使用value这种简单方式
    	// 如@ComponentScan(basePackages = {"xxx.yyy.pkg"})，则可以使用@ComponentScan({"xxx.yyy.pkg"})
    	@AliasFor("basePackages")
    	String[] value() default { };
    	
    	// 设置要扫描的包路径
    	@AliasFor("value")
    	String[] basePackages() default { };
    	// 设置要扫描的类
    	Class<?>[] basePackageClasses() default { };
    	// 设置是否自动获取加了@Component，@Service，@Controller等注解的类
    	boolean useDefaultFilters() default true;
    	// 设置要排除的扫描信息
    	Filter[] excludeFilters() default { };
    }

## 2：基础类准备 ##

### 2.1：包pack1 ###

package yudaosourcecode.componentscantest.pack1;
    
    import org.springframework.stereotype.Component;
    
    @Component
    public class Component1 { 
    }

package yudaosourcecode.componentscantest.pack1;
    
    import org.springframework.stereotype.Component;
    
    @Component
    public class Component2 {   
      
    }

### 2.2：包pack3 ###

package yudaosourcecode.componentscantest.pack3;
    
    import org.springframework.stereotype.Component;
    
    @Component
    public class Component3 { 
    }

## 3：注解方式测试 ##

### 3.1：测试代码 ###

// 设置只扫描pack1，此时pack3不会被扫描到
    @ComponentScan(basePackages = {  "yudaosourcecode.componentscantest.pack1" })
    public class ComponentScanAnnotationDemo { 
    
        // 打印相关信息
        private static void show(ApplicationContext context) { 
            String[] beans = { "component1", "component2", "component3"};
    
            for (String b : beans) { 
                boolean isContains = context.containsBean(b);
                System.out.println(b + " is exist : " + isContains);
                if (isContains) { 
                    System.out.println(b + " : " + context.getBean(b));
                }
            }
        }
    
        /** * 通过AnnotationConfigApplicationContext 触发@ComponentScan使用 */
        public static void triggerViaAnnotationConfigApplicationContext() { 
            //加载@ComponentScan 的包扫描
            try (AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext()) { 
                context.register(ComponentScanAnnotationDemo.class);
                context.refresh();
    
                show(context);
            }
        }
    
        public static void main(String[] args) { 
            AnnotationConfigApplicationContext context =
                    new AnnotationConfigApplicationContext();
            // 注册配置信息类
            context.register(ComponentScanAnnotationDemo.class);
            // 刷新容器，创建spring bean
            context.refresh();
    
            // 判断spring bean信息
            String[] beans = { "component1", "component2", "component3"};
            for (String bean : beans) { 
                if (context.containsBean(bean)) { 
                    System.out.println(bean + " is: " + context.getBean(bean));
                } else { 
                    System.out.println(bean + " is not contains");
                }
            }
        }
    }

只设置了`basePackages = { "yudaosourcecode.componentscantest.pack1" }`只会扫描pack1，因此运行只会存在`component1`，`component2`,运行如下：

component1 is: yudaosourcecode.componentscantest.pack1.Component1@87f383f
    component2 is: yudaosourcecode.componentscantest.pack1.Component2@4eb7f003
    component3 is not contains

通过添加`basePackageClasses = { yudaosourcecode.componentscantest.pack3.Component3.class }`加入扫描pack3中的Component3类，则会加入`component3`，修改后如下：

@ComponentScan(basePackages = {  "yudaosourcecode.componentscantest.pack1" },
    basePackageClasses = {  yudaosourcecode.componentscantest.pack3.Component3.class })

运行如下：

component1 is: yudaosourcecode.componentscantest.pack1.Component1@eafc191
    component2 is: yudaosourcecode.componentscantest.pack1.Component2@612fc6eb
    component3 is: yudaosourcecode.componentscantest.pack3.Component3@1060b431

增加`excludeFilters = @ComponentScan.Filter(type = FilterType.ASSIGNABLE_TYPE, value = yudaosourcecode.componentscantest.pack1.Component2.class)`排除pack1中的component2，修改后如下:

@ComponentScan(basePackages = {  "yudaosourcecode.componentscantest.pack1" },
    basePackageClasses = {  yudaosourcecode.componentscantest.pack3.Component3.class },
    excludeFilters = @ComponentScan.Filter(type = FilterType.ASSIGNABLE_TYPE, value = yudaosourcecode.componentscantest.pack1.Component2.class))

运行如下：

component1 is: yudaosourcecode.componentscantest.pack1.Component1@491cc5c9
    component2 is not contains
    component3 is: yudaosourcecode.componentscantest.pack3.Component3@74ad1f1f

## 4：xml配置文件方式测试 ##

### 4.1：扫描配置 ###

// 设置扫描pack1，此时结果为pack1#Component1，pack1#Component2
    @ComponentScan(basePackages = {  "yudaosourcecode.componentscantest.pack1" },
    // 设置扫描pack3中Component3，此时结果为pack1#Component1，pack1#Component2，pack3#Component3
    basePackageClasses = {  yudaosourcecode.componentscantest.pack3.Component3.class },
    // 设置排除pack1中Component2类，最终结果为pack1#Component1，pack3#Component3
    excludeFilters = @ComponentScan.Filter(type = FilterType.ASSIGNABLE_TYPE, value = yudaosourcecode.componentscantest.pack1.Component2.class))

### 4.2：xml ###

<?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/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd">
        
        <context:annotation-config/>
        
        <bean class="yudaosourcecode.componentscantest.ComponentScanAnnotationDemo"/>
    </beans>

### 4.3：测试代码 ###

@Test
    publicvoid componentscantest() { 
        ClassPathXmlApplicationContext context
                = new ClassPathXmlApplicationContext("componentscantest/componentscantest.xml");
    
        // 判断spring bean信息
        String[] beans = { "component1", "component2", "component3"};
        for (String bean : beans) { 
            if (context.containsBean(bean)) { 
                System.out.println(bean + " is: " + context.getBean(bean));
            } else { 
                System.out.println(bean + " is not contains");
            }
        }
    }

### 4.4：运行 ###

component1 is: yudaosourcecode.componentscantest.pack1.Component1@436a4e4b
    component2 is not contains
    component3 is: yudaosourcecode.componentscantest.pack3.Component3@f2f2cc1