标签：return config 分析 版本 构建 log 情况 standard opera
打开上面任意一个AutoConfiguration文件，一般都有下面的条件注解，在spring-boot-autoconfigure-1.5.3.RELEASE.jar的org.springframework.boot.autoconfigure.condition包下条件注解如下：
这些注解都组合了@Conditional元注解，只是使用了不同的条件（Conditional），Spring 条件注解（@Conditional）我们介绍过根据不同条件创建不同Bean。
简单分析一下@ConditionalOnWebApplication注解：
package org.springframework.boot.autoconfigure.condition;
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.context.annotation.Conditional;
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnWebApplicationCondition.class)
public @interface ConditionalOnWebApplication {
}
从源码我们可以看出，此注解使用的条件是OnWebApplicationCondition类，下面我们看看这个类是怎么构造的：
package org.springframework.boot.autoconfigure.condition;
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.core.type.AnnotatedTypeMetadata;
import org.springframework.util.ClassUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.StandardServletEnvironment;
@Order(Ordered.HIGHEST_PRECEDENCE + 20)
class OnWebApplicationCondition extends SpringBootCondition {
private static final String WEB_CONTEXT_CLASS = "org.springframework.web.context."
+ "support.GenericWebApplicationContext";
@Override
public ConditionOutcome getMatchOutcome(ConditionContext context,
AnnotatedTypeMetadata metadata) {
boolean webApplicationRequired = metadata
.isAnnotated(ConditionalOnWebApplication.class.getName());
ConditionOutcome webApplication = isWebApplication(context, metadata);
if (webApplicationRequired && !webApplication.isMatch()) {
return ConditionOutcome.noMatch(webApplication.getMessage());
}
if (!webApplicationRequired && webApplication.isMatch()) {
return ConditionOutcome.noMatch(webApplication.getMessage());
}
return ConditionOutcome.match(webApplication.getMessage());
}
private ConditionOutcome isWebApplication(ConditionContext context,
AnnotatedTypeMetadata metadata) {
if (!ClassUtils.isPresent(WEB_CONTEXT_CLASS, context.getClassLoader())) {
return ConditionOutcome.noMatch("web application classes not found");
}
if (context.getBeanFactory() != null) {
String[] scopes = context.getBeanFactory().getRegisteredScopeNames();
if (ObjectUtils.containsElement(scopes, "session")) {
return ConditionOutcome.match("found web application ‘session‘ scope");
}
}
if (context.getEnvironment() instanceof StandardServletEnvironment) {
return ConditionOutcome
.match("found web application StandardServletEnvironment");
}
if (context.getResourceLoader() instanceof WebApplicationContext) {
return ConditionOutcome.match