一、前言
上篇讲到了spring boot 通过SpringFactoriesLoader.loadFactoryNames进行加载工厂实例名称列表。本篇是接着上篇继续从源码讲解spring boot加载配置文件的流程,
二、代码解读
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
// Use names and ensure unique to protect against duplicates
Set<String> names = new LinkedHashSet<>(
SpringFactoriesLoader.loadFactoryNames(type, classLoader));
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
既然他加载完工厂实例名称列表了,那么他如何初始化呢。我们继续往下看,他有个
createSpringFactoriesInstances()
//用来创建spring工厂实例
private <T> List<T> createSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args,
Set<String> names) {
List<T> instances = new ArrayList<>(names.size());//创建实例list,用来装创建好的实例
for (String name : names) {
try {
Class<?> instanceClass = ClassUtils.forName(name, classLoader);//创建没有被链接的类,此处底层用到了 ClassLoader.loadClass 关于它和 Class.forName的区别 可以参考https://www.cnblogs.com/suibianle/p/6676215.html
Assert.isAssignable(type, instanceClass);//判断instanceClass是否是type类型
Constructor<?> constructor = instanceClass
.getDeclaredConstructor(parameterTypes);//获取instanceClass构造
T instance = (T) BeanUtils.instantiateClass(constructor, args);//实例化
instances.add(instance);
}
catch (Throwable ex) {
throw new IllegalArgumentException(
"Cannot instantiate " + type + " : " + name, ex);
}
}
return instances;
}
经过此方法后,关于type类型的工厂实例就初始化完成了。