写在前面
本章节起始于研究java核心技术卷，不知不觉发现已经有很多特性能够支持自己去进行一些创造，比如说，我可以实现Ioc整个流程，这便是反射的用武之地 再比如说。。。
手撕SpringIoc容器
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
public class BeanContainer {
private final Map<Class<?>, Object> singletons = new HashMap<>();
private final Set<Class<?>> creating = new HashSet<>();
public <T> T getBean(Class<T> type) {
if (singletons.containsKey(type)) {
return type.cast(singletons.get(type));
}
if (creating.contains(type)) {
throw new IllegalStateException("Circular dependency: " + type);
}
creating.add(type);
try {
T instance = createBean(type);
singletons.put(type, instance);
return instance;
} finally {
creating.remove(type);
}
}
private <T> T createBean(Class<T> type) {
try {
Constructor<?> ctor = selectConstructor(type);
Object[] deps = resolveDependencies(ctor);
ctor.setAccessible(true);
return type.cast(ctor.newInstance(deps));
} catch (Exception e) {
throw new RuntimeException(e);
}
}
private Constructor<?> selectConstructor(Class<?> type) {
Constructor<?>[] ctors = type.getDeclaredConstructors();
if (ctors.length != 1) {
throw new IllegalStateException("Only single constructor supported: " + type);
}
return ctors[0];
}
private Object[] resolveDependencies(Constructor<?> ctor) {
Parameter[] params = ctor.getParameters();
Object[] deps = new Object[params.length];
for (int i = 0; i < params.length; i++) {
deps[i] = getBean(params[i].getType());
}
return deps;
}
}
手搓@UUID注解
implements BeanPostProcessor
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
public class UUIDBeanPostProcessor implements BeanPostProcessor {
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
//拿到bean，得到class，
if (bean instanceof BeanPostProcessor) {
return bean;
}
Class cl = bean.getClass();
Field[] fields = cl.getDeclaredFields();
for (Field f : fields) {
if (f.isAnnotationPresent(UUID.class)) {
f.setAccessible(true);
try {
f.set(bean, java.util.UUID.randomUUID().toString());
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
}
}
return bean;
}
}
