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1、Spring Boot 自动装配原理
依赖 @Enable 模块驱动设计模式,@EnableAutoConfiguration 必然会“@Import”ImportSelector 或 ImportBeanDefinitionRegister 的实现类, 查看源码:
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {......}
其中 AutoConfigurationImportSelector 就是 @EnableAutoConfiguration 所需 ”@Import” 的 DeferredImportSelector 实现类，由于 DeferredImportSelector 作为 ImportSeldector 的子接口，所以组件自动装配逻辑均在 selectImports 方法中.
源码:
public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware,
ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered {
......
@Override
// 根据 autoConfigurationMetadata 条件执行过滤
public String[] selectImports(AnnotationMetadata annotationMetadata) {if (!isEnabled(annotationMetadata)) {return NO_IMPORTS;
}
// 加载自动装配的元信息
AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
.loadMetadata(this.beanClassLoader);
// 获取自动装配的类名集合
AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,
annotationMetadata);
return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
}
}
protected AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata,
AnnotationMetadata annotationMetadata) {if (!isEnabled(annotationMetadata)) {return EMPTY_ENTRY;
}
// 获取 @EnableAutoConfiguration 标注类的元信息
AnnotationAttributes attributes = getAttributes(annotationMetadata);
// 获取自动装配的候选类名集合
List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
// 移除重复对象
configurations = removeDuplicates(configurations);
// 获取自动装配排除名单
Set<String> exclusions = getExclusions(annotationMetadata, attributes);
checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
// 根据 autoConfigurationMetadata 条件执行过滤
configurations = filter(configurations, autoConfigurationMetadata);
// 自动装配的导入事件
fireAutoConfigurationImportEvents(configurations, exclusions);
return new AutoConfigurationEntry(configurations, exclusions);
}
解析:
- AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
.loadMetadata(this.beanClassLoader); 加载自动装配的元信息 - AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,
annotationMetadata); 获取自动装配信息 - AnnotationAttributes attributes = getAttributes(annotationMetadata); 获取 @EnableAutoConfiguration 标注类的元信息
- List
configurations = getCandidateConfigurations(annotationMetadata, attributes); 获取自动装配的候选类名集合 - configurations = removeDuplicates(configurations); 移除重复对象
- Set
exclusions = getExclusions(annotationMetadata, attributes);
checkExcludedClasses(configurations, exclusions); 获取自动装配黑名单 - configurations = filter(configurations, autoConfigurationMetadata); 根据 autoConfigurationMetadata 条件执行过滤
- fireAutoConfigurationImportEvents(configurations, exclusions); 自动装配的导入事件
1.1、@EnableAutoConfiguration 读取侯选装配组件
源码:
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {// 获取自动装配组件
List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
getBeanClassLoader());
// 如果需要装配的组件为空
Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you"
+ "are using a custom packaging, make sure that file is correct.");
return configurations;
}
// 获取 Spring Factories 加载工厂类
protected Class<?> getSpringFactoriesLoaderFactoryClass() {return EnableAutoConfiguration.class;
}
// 通过名字讲行加载
public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {String factoryTypeName = factoryType.getName();
return (List)loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());
}
// 装载 Spring Factories 工厂机制
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {// 从缓存中获取
MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
if (result != null) {return result;
} else {try {// 搜索指定 Classpath 下所有的 META-INF/spring.factories 资源内容
Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
LinkedMultiValueMap result = new LinkedMultiValueMap();
// 循环遍历 spring.factories 资源内容
while(urls.hasMoreElements()) {URL url = (URL)urls.nextElement();
UrlResource resource = new UrlResource(url);
// 将资源内容制作为 properties 文件
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
Iterator var6 = properties.entrySet().iterator();
// 合并为一个 key 为接口全类名,value 是实现类全类名列表
while(var6.hasNext()) {Entry<?, ?> entry = (Entry)var6.next();
// 接口全类名
String factoryTypeName = ((String)entry.getKey()).trim();
String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
int var10 = var9.length;
for(int var11 = 0; var11 < var10; ++var11) {// 实现类全类名
String factoryImplementationName = var9[var11];
result.add(factoryTypeName, factoryImplementationName.trim());
}
}
}
// 放入缓存
cache.put(classLoader, result);
return result;
} catch (IOException var13) {throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);
}
}
}
1.2、@EnableAutoConfiguration 排除自动装配组件
源码:
// 获取要排除的自动装配组件
protected Set<String> getExclusions(AnnotationMetadata metadata, AnnotationAttributes attributes) {// 用于存储排除名单
Set<String> excluded = new LinkedHashSet<>();
// 添加排除类,spring.autoconfigure.exclude
excluded.addAll(asList(attributes, "exclude"));
// 添加排除类名,spring.autoconfigure.excludeName excluded.addAll(Arrays.asList(attributes.getStringArray("excludeName")));
// 添加所有的自动装配排除集合, 用于后面检查类名集合是否合法
excluded.addAll(getExcludeAutoConfigurationsProperty());
return excluded;
}
1.3、@EnableAutoConfiguration 过滤自动装配组件
源码:
// 获取要过滤的自动装配组件
private List<String> filter(List<String> configurations, AutoConfigurationMetadata autoConfigurationMetadata) {long startTime = System.nanoTime();
// 将自动装配类名转化为字符串数组
String[] candidates = StringUtils.toStringArray(configurations);
boolean[] skip = new boolean[candidates.length];
boolean skipped = false;
for (AutoConfigurationImportFilter filter : getAutoConfigurationImportFilters()) {invokeAwareMethods(filter);
// 查检是否匹配
boolean[] match = filter.match(candidates, autoConfigurationMetadata);
for (int i = 0; i < match.length; i++) {// 如果需要过滤
if (!match[i]) {skip[i] = true;
candidates[i] = null;
skipped = true;
}
}
}
// 如果不需要过滤, 直接返回
if (!skipped) {return configurations;
}
List<String> result = new ArrayList<>(candidates.length);
// 如果需要过滤, 将过滤后的对象放入 result
for (int i = 0; i < candidates.length; i++) {if (!skip[i]) {result.add(candidates[i]);
}
}
if (logger.isTraceEnabled()) {int numberFiltered = configurations.size() - result.size();
logger.trace("Filtered" + numberFiltered + "auto configuration class in"
+ TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime) + "ms");
}
// 返回过滤后的类名集合
return new ArrayList<>(result);
}
// 获取由所有 ImportFilters 集合
protected List<AutoConfigurationImportFilter> getAutoConfigurationImportFilters() {return SpringFactoriesLoader.loadFactories(AutoConfigurationImportFilter.class, this.beanClassLoader);
}
2、自定义 Spring Boot Starter
2.1、新添加 Maven 工程
pom.xml 文件如下:
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.tyschool</groupId>
<artifactId>formatter-spring-boot-starter</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
<version>2.2.6.RELEASE</version>
<optional>true</optional>
</dependency>
</dependencies>
</project>
2.2、新建格式化接口
public interface Formatter {String format(Object obj);
}
2.3、实现接口
public class DefaultFormatter implements Formatter {public String format(Object obj) {return String.valueOf(obj);
}
}
2.4、实现 DefaultFormatter 自动装配
@Configuration
public class FormatterAutoConfiguration {@Bean
public Formatter defaultFormatter(){return new DefaultFormatter();}
}
2.5、在 META-INF/spring.factories 资源声明 FormatterAutoConfiguration
# FormatterAutoConfiguration 自动装配声明
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.tyschool.autoconfigure.config.FormatterAutoConfiguration
2.6、构建 Spring Boot Starter
mvn -Dmaven.test.skip -U clean install
2.7、添加 formatter-spring-boot-starter 依赖
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
<version>2.2.6.RELEASE</version>
<optional>true</optional>
</dependency>
<dependency>
<groupId>com.tyschool</groupId>
<artifactId>formatter-spring-boot-starter</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
</dependencies>
2.8、新建引导类
@SpringBootApplication
public class FormatterBootStrap {public static void main(String[] args) {// 创建 Spring 上下文
ConfigurableApplicationContext context = new SpringApplicationBuilder(FormatterBootStrap.class)
.web(WebApplicationType.NONE)
.run(args);
Map<String, Object> map = new HashMap<String, Object>();
map.put("name","tyschool");
// 获取 bean
Formatter formatter = context.getBean(Formatter.class);
// 格式化数据并输出
System.out.println(formatter.format(map));
context.close();}
}
正文完
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