Spring@Component自定义注解实现详解

package com.nightcat.annotaion;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
    String title() default "";
    int type() default 0;
}

package com.nightcat.bean;
import com.nightcat.annotaion.MyAnnotation;
@MyAnnotation(title = "《好好学习》", type = 1)
public class Article {
}

package com.nightcat.test;
import com.nightcat.annotaion.MyAnnotation;
import com.nightcat.bean.Article;
public class AnnotationTest {
    public static void main(String[] args) {
        Class<Article> articleClass = Article.class;
        MyAnnotation annotation = articleClass.getAnnotation(MyAnnotation.class);
        System.out.println("annotation.title() = " + annotation.title()); //《好好学习》
        System.out.println("annotation.type() = " + annotation.type());// 1
    }
}

//
// Source code recreated from a .class file by IntelliJ idea
// (powered by Fernflower decompiler)
//
package com.nightcat.annotaion;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
    String title() default "";
    int type() default 0;
}

package com.nightcat.annotaion;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface MyComponent {
}

package com.nightcat.bean;
import com.nightcat.annotaion.MyComponent;
@MyComponent
public class Student {
    private Integer age;
    private String stuName;
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public String getStuName() {
        return stuName;
    }
    public void setStuName(String stuName) {
        this.stuName = stuName;
    }
    @Override
    public String toString() {
        return "Student{" +
                "age=" + age +
                ", stuName='" + stuName + '\'' +
                '}';
    }
}

package com.nightcat;
import com.nightcat.annotaion.MyComponent;
import java.io.File;
import java.net.URL;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.logging.Logger;
public class ApplicationContext {
    private Logger logger = Logger.getLogger(ApplicationContext.class.toString());
    private Map<String, Object> ioc = new ConcurrentHashMap();
    public Object getBean(String beanName) {
        return ioc.get(beanName);
    }
    public ApplicationContext(String packagePath) {
        scanPackagePath(packagePath);
    }
    private void scanPackagePath(String packagePath) {
        File file = getFile(packagePath);
        File[] allFile = getAllFile(packagePath, file);
        handleClassFile(packagePath, allFile);
    }
    private void handleClassFile(String packagePath, File[] allClassFile) {
        for (File file : allClassFile) {
            String classFileName = file.getName();
            String fileName = classFileName.substring(0, classFileName.lastIndexOf("."));
            String beanName = String.valueOf(fileName.charAt(0)).toLowerCase() + fileName.substring(1);
            String fullClassName = packagePath + "." + fileName;
            try {
                Class<?> aClass = Class.forName(fullClassName);
                if (aClass.isAnnotationPresent(MyComponent.class)) {
                    Object o = aClass.newInstance();
                    ioc.put(beanName, o);
                }
            } catch (Exception e) {
                logger.warning("实例化异常");
            }
        }
    }
    private File[] getAllFile(String packagePath, File file) {
        File[] files = file.listFiles(file1 -> {
            if (file1.isDirectory()) {
                scanPackagePath(packagePath + "." + file1.getName());
            } else {
                String name = file1.getName();
                if (name.endsWith(".class")) return true;
                else return false;
            }
            return false;
        });
        return files;
    }
    private File getFile(String packagePath) {
        String dirPath = packagePath.replaceAll("\\.", "/");
        URL url = this.getClass().getClassLoader().getResource(dirPath);
        String fileName = url.getFile();
        return new File(fileName);
    }
}

package com.nightcat.test;
import com.nightcat.ApplicationContext;
import com.nightcat.bean.Student;
public class CodeTest {
    public static void main(String[] args) {
        ApplicationContext context = new ApplicationContext("com.nightcat");
        Student student = (Student) context.getBean("student");
        System.out.println(student);
    }
}