背景
Spring Boot Starters 提供了很多常用的组件，有些组件例如 Kafka 和 RocketMQ，引入到工程后会自动装配，它会检查您的配置，跟外部的组件创建一些连接，这个时候，我们很难控制 Kafka 关闭，RocketMQ 开启。
目标
给 Spring Boot Starters 的组件提供一个开关，控制自动装配。
实现
Spring Boot AutoCofiguration 提供了 AutoConfigurationImportFilter 过滤器，用来控制 @Configuration 配置类是否生效。查看 AutoConfigurationImportSelector 的源码，它会去调用 AutoConfigurationImportFilter 过滤器，传入所有的 @Configuration 配置类，通过 filter 方法筛选掉不需要的配置类，返回最新的配置类集合。
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| public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered {
private static class ConfigurationClassFilter {
private final AutoConfigurationMetadata autoConfigurationMetadata;
private final List<AutoConfigurationImportFilter> filters;
ConfigurationClassFilter(ClassLoader classLoader, List<AutoConfigurationImportFilter> filters) {
this.autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(classLoader);
this.filters = filters;
}
protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
if (!isEnabled(annotationMetadata)) {
return EMPTY_ENTRY;
}
configurations = getConfigurationClassFilter().filter(configurations);
fireAutoConfigurationImportEvents(configurations, exclusions);
return new AutoConfigurationEntry(configurations, exclusions);
}
List<String> filter(List<String> configurations) {
long startTime = System.nanoTime();
String[] candidates = StringUtils.toStringArray(configurations);
boolean skipped = false;
for (AutoConfigurationImportFilter filter : this.filters) {
boolean[] match = filter.match(candidates, this.autoConfigurationMetadata);
for (int i = 0; i < match.length; i++) {
if (!match[i]) {
candidates[i] = null;
skipped = true;
}
}
}
if (!skipped) {
return configurations;
}
}
}
}
|
以 Kafka 为例，我们可以在 src/main/resources/META-INF 添加 spring.factories 文件，内容如下：
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|
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.ylzl.spring.boot.kafka.autoconfigure.KafkaAutoConfigurationImportFilter
|
对应的代码实现如下：
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| public class KafkaAutoConfigurationImportFilter implements AutoConfigurationImportFilter, EnvironmentAware {
private static final String MATCH_KEY = "spring.kafka.enabled";
private static final String[] IGNORE_CLASSES = {
"org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration",
"org.springframework.boot.actuate.autoconfigure.metrics.KafkaMetricsAutoConfiguration"
};
private Environment environment;
@Override
public void setEnvironment(@NotNull Environment environment) {
this.environment = environment;
}
@Override
public boolean[] match(String[] autoConfigurationClasses, AutoConfigurationMetadata autoConfigurationMetadata) {
boolean disabled = !Boolean.parseBoolean(environment.getProperty(MATCH_KEY, Conditions.TRUE));
boolean[] match = new boolean[autoConfigurationClasses.length];
for (int i = 0; i < autoConfigurationClasses.length; i++) {
int index = i;
match[i] = !disabled || Arrays.stream(IGNORE_CLASSES).noneMatch(e -> e.equals(autoConfigurationClasses[index]));
}
return match;
}
}
|
代码扩展完成，当设置 spring.kafka.enabled=true 时开启 Kafka，设置 spring.kafka.enabled=false 时关闭 Kafka。
产出
- 支持工程内同时存在多种竞品组件，允许您按需开启和关闭。
- 解决第三方组件自动装配的问题，例如第三方项目，一个依赖引入多项配置，这些配置我们用不到，又修改不了相关源码，需要从扩展点屏蔽。
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