自定义Spring Boot Starter实现

1. 依赖导入
 
     
         org.springframework.boot
         spring-boot-starter
     
     
         org.springframework.boot
         spring-boot-starter-web
     
 

2. 过滤器定义
public class LogFilter implements Filter {

    private Logger logger = LoggerFactory.getLogger(LogFilter.class);

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        logger.info("logFilter init...");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
throws IOException, ServletException {
        //  从request中获取到访问的地址，并在控制台中打印出来
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        logger.info("uri {} is working.", request.getRequestURI());
        filterChain.doFilter(servletRequest, servletResponse);
    }

    @Override
    public void destroy() {
        logger.info("logFilter destroy...");
    }
}

3. 将过滤器封装成Spring Bean
public class LogFilterRegistrationBean extends FilterRegistrationBean {

    public LogFilterRegistrationBean() {
        super();
        this.setFilter(new LogFilter()); 
        this.addUrlPatterns("/*"); 
        this.setName("LogFilter");
        this.setOrder(1); 
    }
}

4. 定义自动配置类
@Configuration
@ConditionalOnClass({LogFilterRegistrationBean.class, LogFilter.class})
public class LogFilterAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean(LogFilterRegistrationBean.class)
    public LogFilterRegistrationBean logFilterRegistrationBean() {
        return new LogFilterRegistrationBean();
    }
}

5. 自动配置类生效
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableLogFilterImportSelector.class) 
// 可直接引入LogFilterAutoConfiguration配置类
// 通过引入ImportSelector来获取spring.factories中需要加载的自动配置类
public @interface EnableLogFilter {

}
自定义注解的目的是使LogFilterAutoConfiguration配置类生效，自定义的starter中对应的classes并不在项目的spring扫描范围之内，故无法引入项目的spring管理之中。

public class EnableLogFilterImportSelector
        implements DeferredImportSelector, BeanClassLoaderAware, EnvironmentAware {

    private static final Logger logger = LoggerFactory.getLogger(EnableLogFilterImportSelector.class);

    private ClassLoader beanClassLoader;

    private Class annotationClass = EnableLogFilter.class;

    private Environment environment;

    @Override
    public String[] selectImports(AnnotationMetadata metadata) {
        // 是否生效，默认为true
        if (!isEnabled()) {
            return new String[0];
        }
        // 获取注解中的属性
        AnnotationAttributes attributes = AnnotationAttributes.fromMap(
                metadata.getAnnotationAttributes(this.annotationClass.getName(), true));

        Assert.notNull(attributes, "No " + getSimpleName() + " attributes found. Is "
                + metadata.getClassName() + " annotated with @" + getSimpleName() + "?");
        // 从spring.factories中获取所有通过EnableLogFilter注解引入的自动配置类，并进行去重操作
        List factories = new ArrayList<>(new LinkedHashSet<>(SpringFactoriesLoader
                .loadFactoryNames(this.annotationClass, this.beanClassLoader)));

        if (factories.isEmpty() && !hasDefaultFactory()) {
            throw new IllegalStateException("Annotation @" + getSimpleName()
                    + " found, but there are no implementations. Did you forget to include a starter?");
        }

        if (factories.size() > 1) {
            logger.warn("More than one implementation " + "of @" + getSimpleName()
                    + " (now relying on @Conditionals to pick one): " + factories);
        }

        return factories.toArray(new String[factories.size()]);
    }

    protected boolean hasDefaultFactory() {
        return false;
    }

    protected boolean isEnabled() {
        return true;
    }

    protected String getSimpleName() {
        return this.annotationClass.getSimpleName();
    }

    protected Class getAnnotationClass() {
        return this.annotationClass;
    }

    protected Environment getEnvironment() {
        return this.environment;
    }

    @Override
    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }

    @Override
    public void setBeanClassLoader(ClassLoader classLoader) {
        this.beanClassLoader = classLoader;
    }
}

6. 自动配置类
在resources/META-INF/spring.factories中增加相关配置com.XXX.EnableLogFilter=com.XXX.LogFilterAutoConfiguration

7. 自定义starter的使用

    com.XXX
    XXX-log-filter-starter
    0.0.1-SNAPSHOT

@SpringBootApplication
@EnableLogFilter
public class SpringbootDemoApplication{

    public static void main(String[] args) {
        SpringApplication.run(SpringbootDemoApplication.class, args);
    }
}