说明
Spring核心功能基本可以划分为两个，即IOC（DI）与AOP。IOC与DI本质上是在不同角度对同一件事物对的描述，本文则着手于实现简易得到IOC（DI），AOP在在另一篇文章中单独实现。
注解类
- YComponent
package indi.yp.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.stereotype.Component;
/**
* @ClassName: YComponent
* @author yPan
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Component
public @interface YComponent {
String value() default "";
}
- YAutowried
package indi.yp.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* @ClassName: YAutowired
* @author yPan
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface YAutowired {
}
普通组件
- ComponentA
package indi.yp.component;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import indi.yp.annotation.YComponent;
/**
* @ClassName: ComponentA
* @author yPan
*/
@YComponent
public class ComponentA {
private static final Logger LOGGER = LoggerFactory.getLogger(ComponentA.class);
public void say() {
LOGGER.info("A.say!");
}
}
- ComponentB
package indi.yp.component;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import indi.yp.annotation.YAutowired;
import indi.yp.annotation.YComponent;
/**
* @ClassName: ComponentB
* @author yPan
*/
@YComponent
public class ComponentB {
private static final Logger LOGGER = LoggerFactory.getLogger(ComponentB.class);
@YAutowired
private ComponentA componentA;
public void say() {
componentA.say();
LOGGER.info("B.say!");
}
}
核心实现
- 变量说明
// 扫描包的路径
String packageName = "indi.yp";
// 所有类的集合
List<String> clazzs = new ArrayList<>();
// IOC容器
Map<String, Object> ioc = new HashMap<>();
- 扫描包并且保存class集合
public static void doScan(String packageName, List<String> clazzs) {
String path = Application.class.getResource("/" + packageName.replaceAll("\\.", "/")).getPath();
LOGGER.info("path:{}", path);
File file = new File(path);
for (File tmp : file.listFiles()) {
if (tmp.isDirectory()) {
doScan(packageName + "." + tmp.getName(), clazzs);
} else {
clazzs.add(packageName + "." + StringUtils.replace(tmp.getName(), ".class", ""));
}
}
}
- 创建IOC容器
public static void doIoc(List<String> clazzs, Map<String, Object> ioc) {
clazzs.forEach(x -> {
try {
Class<?> clazz = Class.forName(x);
// 被YComponent注解了
if (clazz.isAnnotationPresent(YComponent.class)) {
YComponent yComponent = clazz.getAnnotation(YComponent.class);
LOGGER.info("clazz.name:{},component.value:{}", clazz.getSimpleName(), yComponent.value());
try {
Object instance = clazz.newInstance();
if (StringUtils.isBlank(yComponent.value())) {
ioc.put(lowwerFirstLetter(clazz.getSimpleName()), instance);
} else {
ioc.put(lowwerFirstLetter(clazz.getSimpleName()), instance);
ioc.put(yComponent.value(), instance);
}
} catch (InstantiationException e) {
LOGGER.error(e.getMessage(), e);
} catch (IllegalAccessException e) {
LOGGER.error(e.getMessage(), e);
}
}
} catch (ClassNotFoundException e) {
LOGGER.error(e.getMessage(), e);
}
});
}
- 实现依赖注入
public static void doAutowired(Map<String, Object> ioc) {
ioc.forEach((x, y) -> {
Field[] fields = y.getClass().getDeclaredFields();
for (Field field : fields) {
// 被YAutowired注解了
if (field.isAnnotationPresent(YAutowired.class)) {
Object obj = null;
if (ioc.containsKey(field.getName())) {
obj = ioc.get(field.getName());
} else {
obj = ioc.get(lowwerFirstLetter(field.getType().getSimpleName()));
}
if (null == obj) {
LOGGER.warn("class :{} can not find component : {}", y.getClass(), field.getName());
return;
}
try {
// 暴力访问私有属性
field.setAccessible(true);
field.set(y, obj);
} catch (IllegalArgumentException e) {
LOGGER.error(e.getMessage(), e);
} catch (IllegalAccessException e) {
LOGGER.error(e.getMessage(), e);
}
}
}
});
}
- 首字母小写
private static String lowwerFirstLetter(String s) {
char[] chars = s.toCharArray();
String firstChar = String.valueOf(chars[0]);
chars[0] = firstChar.toLowerCase().charAt(0);// 转小写
LOGGER.info("s:{},return:{}", s, String.valueOf(chars));
return String.valueOf(chars);
}
总结说明
- 代码
// 扫描包
doScan(packageName, clazzs);
LOGGER.info("clazzs:{}", JSONObject.toJSONString(clazzs));
// IOC容器
doIoc(clazzs, ioc);
LOGGER.info("ioc:{}", JSONObject.toJSONString(ioc));
// autowired
doAutowired(ioc);
// test
ComponentB componentB = (ComponentB) ioc.get("componentB");
componentB.say();
