SpringBoot 进阶篇

@Componentpublic class User{}复制代码

@SpringBootApplicationpublic class SpringbootConditionApplication {	public static void main(String[] args) {		ConfigurableApplicationContext context = SpringApplication.run(SpringbootConditionApplication.class, args);        Object user = context.getBean("user");        System.out.println(user);    }}复制代码

public class ClassCondition 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。 可以用于获取注解定义的属性值     * @return     */    @Override    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {      //1.需求： 导入Jedis坐标后创建Bean        //思路：判断redis.clients.jedis.Jedis.class文件是否存在        boolean flag = true;        try {            Class<?> cls = Class.forName("redis.clients.jedis.Jedis");        } catch (ClassNotFoundException e) {            flag = false;        }        return flag;    }}复制代码

@Configurationpublic class UserConfig {    @Bean    @Conditional(ClassCondition.class)    public User user(){        return new User();    }}复制代码

@SpringBootApplicationpublic class SpringbootConditionApplication {

    public static void main(String[] args) {      //启动SpringBoot的应用，返回Spring的IOC容器      ConfigurableApplicationContext context = SpringApplication.run(SpringbootConditionApplication.class, args);
      Object user = context.getBean("user");      System.out.println(user);
    }}复制代码

import org.springframework.context.annotation.Conditional;import java.lang.annotation.*;
@Target({ElementType.TYPE, ElementType.METHOD})@Retention(RetentionPolicy.RUNTIME)@Documented@Conditional(ClassCondition.class) //此处@ConditionOnClass为自定义注解public @interface ConditionOnClass {    String[] value();}复制代码

@Configurationpublic class UserConfig {
    @Bean    //@Conditional(ClassCondition.class)    @ConditionOnClass("com.alibaba.fastjson.JSON")    public User user(){        return new User();    }         @Bean    @ConditionalOnProperty(name = "itcast",havingValue = "itheima")    public User user2(){        return new User();    }
}复制代码

@SpringBootApplicationpublic class SpringbootConditionApplication {

  public static void main(String[] args) {        //启动SpringBoot的应用，返回Spring的IOC容器        ConfigurableApplicationContext context = SpringApplication.run(SpringbootConditionApplication.class, args);
        Object user = context.getBean("user");        System.out.println(user);    }
}复制代码

  <dependency>        <groupId>org.springframework.boot</groupId>        <artifactId>spring-boot-starter-web</artifactId>        <!--排除tomcat依赖-->        <exclusions>            <exclusion>                <artifactId>spring-boot-starter-tomcat</artifactId>                <groupId>org.springframework.boot</groupId>            </exclusion>        </exclusions>    </dependency>                <!--引入jetty的依赖-->        <dependency>            <artifactId>spring-boot-starter-jetty</artifactId>            <groupId>org.springframework.boot</groupId>        </dependency>复制代码

SpringBoot中提供了很多Enable开头的注解，这些注解都是用于动态启用某些功能的。而其底层原理是使用@Import注解导入一些配置类，实现Bean的动态加载.
SpringBoot不能直接获取在其他工程中定义的Bean复制代码

** * @ComponentScan 扫描范围：当前引导类所在包及其子包 * * com.itheima.springbootenable * com.itheima.config * //1.使用@ComponentScan扫描com.itheima.config包 * //2.可以使用@Import注解，加载类。这些类都会被Spring创建，并放入IOC容器 * //3.可以对Import注解进行封装。 */  //@ComponentScan("com.cf.config")//@Import(UserConfig.class)@EnableUser@SpringBootApplicationpublic class SpringbootEnableApplication {
    public static void main(String[] args) {        ConfigurableApplicationContext context = SpringApplication.run(SpringbootEnableApplication.class, args);        //获取Bean        Object user = context.getBean("user");        System.out.println(user);	}}复制代码