目录一、SpringBootApplication二、案例三、Condition四、案例升级五、小结
一、SpringBootApplication
@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@SpringBootConfiguration@EnableAutoConfiguration@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })public @interface SpringBootApplication {
@Target(ElementType.TYPE)
设置当前注解可以标记在哪里，而SpringBootApplication只能用在类上面还有一些其他的设置
public enum ElementType { /** Class, interface (including annotation type), or enum declaration */ TYPE, /** Field declaration (includes enum constants) */ FIELD, /** Method declaration */ METHOD, /** Formal parameter declaration */ PARAMETER, /** Constructor declaration */ CONSTRUCTOR, /** Local variable declaration */ LOCAL_VARIABLE, /** Annotation type declaration */ ANNOTATION_TYPE, /** Package declaration */ PACKAGE, /** * Type parameter declaration * * @since 1.8 */ TYPE_PARAMETER, /** * Use of a type * * @since 1.8 */ TYPE_USE, /** * Module declaration. * * @since 9 */ MODULE}
@Retention(RetentionPolicy.RUNTIME)
public enum RetentionPolicy { /** * Annotations are to be discarded by the compiler. */ SOURCE, /** * Annotations are to be recorded in the class file by the compiler * but need not be retained by the VM at run time. This is the default * behavior. */ CLASS, /** * Annotations are to be recorded in the class file by the compiler and * retained by the VM at run time, so they may be read reflectively. * * @see java.lang.reflect.AnnotatedElement */ RUNTIME}
SOURCE 当编译时，注解将不会出现在class源文件中
CLASS 注解将会保留在class源文件中，但是不会被jvm加载，也就意味着不能通过反射去找到该注解，因为没有加载到java虚拟机中
RUNTIME是既会保留在源文件中，也会被虚拟机加载
@Documented
java doc 会生成注解信息
@Inherited
是否会被继承，就是如果一个子类继承了使用了该注解的类，那么子类也能继承该注解
@SpringBootConfiguration
标注在某个类上，表示这是一个Spring Boot的配置类，本质上也是使用了@Configuration注解
@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Configurationpublic @interface SpringBootConfiguration {
@EnableAutoConfiguration
@EnableAutoConfiguration告诉SpringBoot开启自动配置，会帮我们自动去加载 自动配置类
@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@AutoConfigurationPackage@Import({AutoConfigurationImportSelector.class})public @interface EnableAutoConfiguration {
@AutoConfigurationPackage
将当前配置类所在包保存在BasePackages的Bean中。供Spring内部使用
@Import({AutoConfigurationImportSelector.class})来加载配置类
配置文件的位置：META-INF/spring.factories,该配置文件中定义了大量的配置类，当springboot启动时，会自动加载这些配置类，初始化Bean
并不是所有Bean都会被初始化，在配置类中使用Condition来加载满足条件的Bean
二、案例
自定义redis-starter，要求当导入redis坐标时，spirngboot自动创建jedis的Bean
步骤
1.创建redis-spring-boot-autoconfigure模块2.创建redis-spring-boot-starter模块，依赖redis-spring-boot-autoconfigure的模块3.在redis-spring-boot-autoconfigure模块中初始化jedis的bean，并定义META-INF/spring.factories文件4.在测试模块中引入自定义的redis-starter依赖，测试获取jedis的bean，操作redis
1.首先新建两个模块
删除一些没有用的东西，和启动类否则会报错
2.redis-spring-boot-starter模块的pom.xml里面引入redis-spring-boot-autoconfigure的模块的坐标
3.RedisAutoConfiguration配置类
package com.blb;import org.springframework.boot.context.properties.EnableConfigurationProperties;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import redis.clients.jedis.Jedis;@Configuration@EnableConfigurationProperties(RedisProperties.class)public class RedisAutoConfiguration {// 提供Jedis的bean @Bean public Jedis jedis(RedisProperties redisProperties){ return new Jedis(redisProperties.getHost(),redisProperties.getPort()); }}
RedisProperties
package com.blb;import org.springframework.boot.context.properties.ConfigurationProperties;@ConfigurationProperties(prefix = "redis")public class RedisProperties { private String host="localhost"; private int port=6379; public String getHost() { return host; } public void setHost(String host) { this.host = host; } public int getPort() { return port; } public void setPort(int port) { this.port = port; }}
@ComponentScan
扫描包 相当于在spring.xml 配置中context:comonent-scan 但是并没有指定basepackage，如果没有指定spring底层会自动扫描当前配置类所有在的包
排除的类型
public enum FilterType {/** * Filter candidates marked with a given annotation. * @see org.springframework.core.type.filter.AnnotationTypeFilter */ANNOTATION,/** * Filter candidates assignable to a given type. * @see org.springframework.core.type.filter.AssignableTypeFilter */ASSIGNABLE_TYPE,/** * Filter candidates matching a given AspectJ type pattern expression. * @see org.springframework.core.type.filter.AspectJTypeFilter */ASPECTJ,/** * Filter candidates matching a given regex pattern. * @see org.springframework.core.type.filter.RegexPatternTypeFilter */REGEX,/** Filter candidates using a given custom * {@link org.springframework.core.type.filter.TypeFilter} implementation. */CUSTOM}
ANNOTATION 默认根据注解的完整限定名设置排除ASSIGNABLE_TYPE 根据类的完整限定名排除ASPECTJ 根据切面表达式设置排除REGEX 根据正则表达式设置排除CUSTOM 自定义设置排除
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
按照自定义的方式来排除需要指定一个类，要实现TypeFilter接口，重写match方法
public class TypeExcludeFilter implements TypeFilter, BeanFactoryAware {public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException { if (this.beanFactory instanceof ListableBeanFactory && this.getClass() == TypeExcludeFilter.class) { Iterator var3 = this.getDelegates().iterator(); while(var3.hasNext()) { TypeExcludeFilter delegate = (TypeExcludeFilter)var3.next(); if (delegate.match(metadataReader, metadataReaderFactory)) { return true; } } } return false; }}
TypeExcludeFilter ：springboot对外提供的扩展类， 可以供我们去按照我们的方式进行排除
AutoConfigurationExcludeFilter ：排除所有配置类并且是自动配置类中里面的其中一个示例
package com.blb.springbootyuanli.config;import org.springframework.boot.context.TypeExcludeFilter;import org.springframework.core.type.classreading.MetadataReader;import org.springframework.core.type.classreading.MetadataReaderFactory;import java.io.IOException;public class MyTypeExcludeFilter extends TypeExcludeFilter { @Override public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException { if(metadataReader.getClassMetadata().getClass()==UserConfig.class){ return true; } return false; }}
三、Condition
@Conditional是Spring4新提供的注解，它的作用是按照一定的条件进行判断，满足条件给容器注册bean，实现选择性的创建bean的操作，该注解为条件装配注解
源码
@Target({ElementType.TYPE, ElementType.METHOD})@Retention(RetentionPolicy.RUNTIME)@Documentedpublic @interface Conditional {/** * All {@link Condition} classes that must {@linkplain Condition#matches match} * in order for the component to be registered. */Class<? extends Condition>[] value();}
@FunctionalInterfacepublic interface Condition {/** * Determine if the condition matches. * @param context the condition context * @param metadata the metadata of the {@link org.springframework.core.type.AnnotationMetadata class} * or {@link org.springframework.core.type.MethodMetadata method} being checked * @return {@code true} if the condition matches and the component can be registered, * or {@code false} to veto the annotated component's registration */boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata);}
重写matches方法如果返回true spring则会帮你创建该对象，否则则不会
springboot提供的常用条件注解
@ConditionalOnProperty：判断文件中是否有对应属性和值才实例化Bean@ConditionalOnClass 检查类在加载器中是否存在对应的类，如果有则被注解修饰的类就有资格被 Spring 容器所注册，否则会被跳过。@ConditionalOnBean 仅仅在当前上下文中存在某个对象时，才会实例化一个 Bean@ConditionalOnClass 某个 CLASS 位于类路径上，才会实例化一个 Bean@ConditionalOnExpression 当表达式为 true 的时候，才会实例化一个 Bean@ConditionalOnMissingBean 仅仅在当前上下文中不存在某个对象时，才会实例化一个 Bean@ConditionalOnMissingClass 某个 CLASS 类路径上不存在的时候，才会实例化一个 Bean
案例
在springIOC容器中有一个User的bean，现要求：引入jedis坐标后，加载该bean，没导入则不加载
实体类
package com.blb.springbootyuanli.entity;public class User { private String name; private int age;get/set
UserConfig
配置类
package com.blb.springbootyuanli.config;import com.blb.springbootyuanli.condition.UserCondition;import com.blb.springbootyuanli.entity.User;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Conditional;import org.springframework.context.annotation.Configuration;@Configurationpublic class UserConfig { @Bean @Conditional(UserCondition.class) public User user(){ return new User(); }}
UserCondition
实现Condition接口，重写matches方法
package com.blb.springbootyuanli.condition;import org.springframework.context.annotation.Condition;import org.springframework.context.annotation.ConditionContext;import org.springframework.core.type.AnnotatedTypeMetadata;public class UserCondition implements Condition { @Override public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) { //思路判断jedis的class文件是否存在 boolean flag=true; try { Class<?> aClass = Class.forName("redis.clients.jedis.Jedis"); } catch (ClassNotFoundException e) { flag=false; } return flag; }}
启动类
package com.blb.springbootyuanli;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.context.ConfigurableApplicationContext;@SpringBootApplicationpublic class SpringbootYuanliApplication { public static void main(String[] args) { ConfigurableApplicationContext app = SpringApplication.run(SpringbootYuanliApplication.class, args); Object user = app.getBean("user"); System.out.println(user); }}
当我们在pom.xml引入jedis的坐标时，就可以打印user对象，当删除jedis的坐标时，运行就会报错 No bean named ‘user’ available
四、案例升级
将类的判断定义为动态的，判断那个字节码文件可以动态指定
自定义一个注解
添加上元注解
package com.blb.springbootyuanli.condition;import org.springframework.context.annotation.Conditional;import java.lang.annotation.*;@Target({ElementType.TYPE, ElementType.METHOD}) //该注解的添加范围@Retention(RetentionPolicy.RUNTIME) //该注解的生效时机@Documented //生成javadoc的文档@Conditional(UserCondition.class)public @interface UserClassCondition { String[] value();}
UserConfig
package com.blb.springbootyuanli.config;import com.blb.springbootyuanli.condition.UserClassCondition;import com.blb.springbootyuanli.entity.User;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;@Configurationpublic class UserConfig { @Bean //@Conditional(UserCondition.class) @UserClassCondition("redis.clients.jedis.Jedis") public User user(){ return new User(); }}
package com.blb.springbootyuanli.condition;import org.springframework.context.annotation.Condition;import org.springframework.context.annotation.ConditionContext;import org.springframework.core.type.AnnotatedTypeMetadata;import java.util.Map;public class UserCondition implements Condition { /** * * @param context 上下文对象，用于获取环境，ioc容器，classloader对象 * @param metadata 注解元对象。可以获取注解定义的属性值 * @return */ @Override public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) { //思路判断指定属性的class文件是否存在 //获取注解属性值 value Map<String,Object> map=metadata.getAnnotationAttributes(UserClassCondition.class.getName()); String[] values= (String[])map.get("value"); boolean flag=true; try { for(String classname:values){ Class<?> aClass = Class.forName(classname); } } catch (ClassNotFoundException e) { flag=false; } return flag; }}
测试自带的注解
package com.blb.springbootyuanli.config;import com.blb.springbootyuanli.entity.User;import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;@Configurationpublic class UserConfig { @Bean //@Conditional(UserCondition.class) //@UserClassCondition("redis.clients.jedis.Jedis") @ConditionalOnProperty(name="age",havingValue = "18") //只有在配置文件中有age并且值为18spring在能注册该bean public User user(){ return new User(); }}
五、小结
自定义条件：
1.定义条件类：自定义类实现Condition接口，重写重写matches方法，在matches方法中进行逻辑判断，返回boolean值
2.matches方法的两个参数：context：上下文对象，可以获取属性值，获取类加载器，获取BeanFactorymetadata：元数据对象，用于获取注解属性
3.判断条件：在初始化Bean时，使用@Conditional（条件类.class） 注解
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