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springboot在初始化过程中,会校验当前项目是否满足web环境,是如何做到的?很简单
在SpringApplication类initialize(Object[] sources)初始化方法里面,第6行是向webEnvironment赋值,调用的是13行的deduceWebEnvironment()方法,
@SuppressWarnings({ "unchecked", "rawtypes" })
private void initialize(Object[] sources) {
if (sources != null && sources.length > 0) {
this.sources.addAll(Arrays.asList(sources));
}
this.webEnvironment = deduceWebEnvironment();
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
private boolean deduceWebEnvironment() {
for (String className : WEB_ENVIRONMENT_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return false;
}
}
return true;
}
这个deduceWebEnvironment会依次遍历String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
"org.springframework.web.context.ConfigurableWebApplicationContext" }
数组,再调用ClassUtils.isPresent(String className, ClassLoader classLoader)方法
public static boolean isPresent(String className, ClassLoader classLoader) {
try {
forName(className, classLoader);
return true;
}
catch (Throwable ex) {
// Class or one of its dependencies is not present...
return false;
}
}
再依次调用forName(String name, ClassLoader classLoader)方法,
public static Class<?> forName(String name, ClassLoader classLoader) throws ClassNotFoundException, LinkageError {
Assert.notNull(name, "Name must not be null");
Class<?> clazz = resolvePrimitiveClassName(name);
if (clazz == null) {
clazz = commonClassCache.get(name);
}
if (clazz != null) {
return clazz;
}
// "java.lang.String[]" style arrays
if (name.endsWith(ARRAY_SUFFIX)) {
String elementClassName = name.substring(0, name.length() - ARRAY_SUFFIX.length());
Class<?> elementClass = forName(elementClassName, classLoader);
return Array.newInstance(elementClass, 0).getClass();
}
// "[Ljava.lang.String;" style arrays
if (name.startsWith(NON_PRIMITIVE_ARRAY_PREFIX) && name.endsWith(";")) {
String elementName = name.substring(NON_PRIMITIVE_ARRAY_PREFIX.length(), name.length() - 1);
Class<?> elementClass = forName(elementName, classLoader);
return Array.newInstance(elementClass, 0).getClass();
}
// "[[I" or "[[Ljava.lang.String;" style arrays
if (name.startsWith(INTERNAL_ARRAY_PREFIX)) {
String elementName = name.substring(INTERNAL_ARRAY_PREFIX.length());
Class<?> elementClass = forName(elementName, classLoader);
return Array.newInstance(elementClass, 0).getClass();
}
ClassLoader clToUse = classLoader;
if (clToUse == null) {
clToUse = getDefaultClassLoader();
}
try {
return (clToUse != null ? clToUse.loadClass(name) : Class.forName(name));
}
catch (ClassNotFoundException ex) {
int lastDotIndex = name.lastIndexOf(PACKAGE_SEPARATOR);
if (lastDotIndex != -1) {
String innerClassName =
name.substring(0, lastDotIndex) + INNER_CLASS_SEPARATOR + name.substring(lastDotIndex + 1);
try {
return (clToUse != null ? clToUse.loadClass(innerClassName) : Class.forName(innerClassName));
}
catch (ClassNotFoundException ex2) {
// Swallow - let original exception get through
}
}
throw ex;
}
}
这个forName方法,最终执行的是ClassLoader.loadClass(String name)方法,简单的说,
分别去加载javax.servlet.Servlet和org.springframework.web.context.ConfigurableWebApplicationContext,如果有一个加载失败,则返回false,即不是web环境