Spring-boot实例化流程

在spring-boot项目中pom文件里面添加的依赖中的bean，是如何注册到spring-boot项目的spring容器中的呢？

spring.factories文件

• 帮助spring-boot项目包以外的bean（即在pom文件中添加依赖中的bean）注册到spring-boot项目的spring容器的
• 由于@ComponentScan注解只能扫描spring-boot项目包内的bean并注册到spring容器中
• 因此需要@EnableAutoConfiguration（在SpringBootApplication下）注解来注册项目包外的bean
• 而spring.factories文件，则是用来记录项目包外需要注册的bean类名

点进去@SpringBootApplication注解

//
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package org.springframework.boot.autoconfigure;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.boot.context.TypeExcludeFilter;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.context.annotation.ComponentScan.Filter;
import org.springframework.core.annotation.AliasFor;

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(
    excludeFilters = {@Filter(
    type = FilterType.CUSTOM,
    classes = {TypeExcludeFilter.class}
), @Filter(
    type = FilterType.CUSTOM,
    classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {
    @AliasFor(
        annotation = EnableAutoConfiguration.class
    )
    Class<?>[] exclude() default {};

    @AliasFor(
        annotation = EnableAutoConfiguration.class
    )
    String[] excludeName() default {};

    @AliasFor(
        annotation = ComponentScan.class,
        attribute = "basePackages"
    )
    String[] scanBasePackages() default {};

    @AliasFor(
        annotation = ComponentScan.class,
        attribute = "basePackageClasses"
    )
    Class<?>[] scanBasePackageClasses() default {};

    @AliasFor(
        annotation = Configuration.class
    )
    boolean proxyBeanMethods() default true;
}

点@EnableAutoConfiguration进去

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package org.springframework.boot.autoconfigure;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Import;

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import({AutoConfigurationImportSelector.class})
public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

    Class<?>[] exclude() default {};

    String[] excludeName() default {};
}

点AutoConfigurationImportSelector进去

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package org.springframework.boot.autoconfigure;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.Aware;
import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.boot.context.properties.bind.Binder;
import org.springframework.context.EnvironmentAware;
import org.springframework.context.ResourceLoaderAware;
import org.springframework.context.annotation.DeferredImportSelector;
import org.springframework.context.annotation.DeferredImportSelector.Group;
import org.springframework.context.annotation.DeferredImportSelector.Group.Entry;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.Environment;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.io.support.SpringFactoriesLoader;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
import org.springframework.core.type.classreading.MetadataReaderFactory;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered {
    private static final AutoConfigurationImportSelector.AutoConfigurationEntry EMPTY_ENTRY = new AutoConfigurationImportSelector.AutoConfigurationEntry();
    private static final String[] NO_IMPORTS = new String[0];
    private static final Log logger = LogFactory.getLog(AutoConfigurationImportSelector.class);
    private static final String PROPERTY_NAME_AUTOCONFIGURE_EXCLUDE = "spring.autoconfigure.exclude";
    private ConfigurableListableBeanFactory beanFactory;
    private Environment environment;
    private ClassLoader beanClassLoader;
    private ResourceLoader resourceLoader;

    public AutoConfigurationImportSelector() {
    }

    public String[] selectImports(AnnotationMetadata annotationMetadata) {
        if (!this.isEnabled(annotationMetadata)) {
            return NO_IMPORTS;
        } else {
            AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);
            AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = this.getAutoConfigurationEntry(autoConfigurationMetadata, annotationMetadata);
            return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
        }
    }

    protected AutoConfigurationImportSelector.AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata, AnnotationMetadata annotationMetadata) {
        if (!this.isEnabled(annotationMetadata)) {
            return EMPTY_ENTRY;
        } else {
            AnnotationAttributes attributes = this.getAttributes(annotationMetadata);
            List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes);
            configurations = this.removeDuplicates(configurations);
            Set<String> exclusions = this.getExclusions(annotationMetadata, attributes);
            this.checkExcludedClasses(configurations, exclusions);
            configurations.removeAll(exclusions);
            configurations = this.filter(configurations, autoConfigurationMetadata);
            this.fireAutoConfigurationImportEvents(configurations, exclusions);
            return new AutoConfigurationImportSelector.AutoConfigurationEntry(configurations, exclusions);
        }
    }

    public Class<? extends Group> getImportGroup() {
        return AutoConfigurationImportSelector.AutoConfigurationGroup.class;
    }

    protected boolean isEnabled(AnnotationMetadata metadata) {
        return this.getClass() == AutoConfigurationImportSelector.class ? (Boolean)this.getEnvironment().getProperty("spring.boot.enableautoconfiguration", Boolean.class, true) : true;
    }

    protected AnnotationAttributes getAttributes(AnnotationMetadata metadata) {
        String name = this.getAnnotationClass().getName();
        AnnotationAttributes attributes = AnnotationAttributes.fromMap(metadata.getAnnotationAttributes(name, true));
        Assert.notNull(attributes, () -> {
            return "No auto-configuration attributes found. Is " + metadata.getClassName() + " annotated with " + ClassUtils.getShortName(name) + "?";
        });
        return attributes;
    }

    protected Class<?> getAnnotationClass() {
        return EnableAutoConfiguration.class;
    }

    protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
        List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader());
        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;
    }

    protected Class<?> getSpringFactoriesLoaderFactoryClass() {
        return EnableAutoConfiguration.class;
    }

    private void checkExcludedClasses(List<String> configurations, Set<String> exclusions) {
        List<String> invalidExcludes = new ArrayList(exclusions.size());
        Iterator var4 = exclusions.iterator();

        while(var4.hasNext()) {
            String exclusion = (String)var4.next();
            if (ClassUtils.isPresent(exclusion, this.getClass().getClassLoader()) && !configurations.contains(exclusion)) {
                invalidExcludes.add(exclusion);
            }
        }

        if (!invalidExcludes.isEmpty()) {
            this.handleInvalidExcludes(invalidExcludes);
        }

    }

    protected void handleInvalidExcludes(List<String> invalidExcludes) {
        StringBuilder message = new StringBuilder();
        Iterator var3 = invalidExcludes.iterator();

        while(var3.hasNext()) {
            String exclude = (String)var3.next();
            message.append("	- ").append(exclude).append(String.format("%n"));
        }

        throw new IllegalStateException(String.format("The following classes could not be excluded because they are not auto-configuration classes:%n%s", message));
    }

    protected Set<String> getExclusions(AnnotationMetadata metadata, AnnotationAttributes attributes) {
        Set<String> excluded = new LinkedHashSet();
        excluded.addAll(this.asList(attributes, "exclude"));
        excluded.addAll(Arrays.asList(attributes.getStringArray("excludeName")));
        excluded.addAll(this.getExcludeAutoConfigurationsProperty());
        return excluded;
    }

    private List<String> getExcludeAutoConfigurationsProperty() {
        if (this.getEnvironment() instanceof ConfigurableEnvironment) {
            Binder binder = Binder.get(this.getEnvironment());
            return (List)binder.bind("spring.autoconfigure.exclude", String[].class).map(Arrays::asList).orElse(Collections.emptyList());
        } else {
            String[] excludes = (String[])this.getEnvironment().getProperty("spring.autoconfigure.exclude", String[].class);
            return excludes != null ? Arrays.asList(excludes) : Collections.emptyList();
        }
    }

    private List<String> filter(List<String> configurations, AutoConfigurationMetadata autoConfigurationMetadata) {
        long startTime = System.nanoTime();
        String[] candidates = StringUtils.toStringArray(configurations);
        boolean[] skip = new boolean[candidates.length];
        boolean skipped = false;
        Iterator var8 = this.getAutoConfigurationImportFilters().iterator();

        while(var8.hasNext()) {
            AutoConfigurationImportFilter filter = (AutoConfigurationImportFilter)var8.next();
            this.invokeAwareMethods(filter);
            boolean[] match = filter.match(candidates, autoConfigurationMetadata);

            for(int i = 0; i < match.length; ++i) {
                if (!match[i]) {
                    skip[i] = true;
                    candidates[i] = null;
                    skipped = true;
                }
            }
        }

        if (!skipped) {
            return configurations;
        } else {
            List<String> result = new ArrayList(candidates.length);

            int numberFiltered;
            for(numberFiltered = 0; numberFiltered < candidates.length; ++numberFiltered) {
                if (!skip[numberFiltered]) {
                    result.add(candidates[numberFiltered]);
                }
            }

            if (logger.isTraceEnabled()) {
                numberFiltered = configurations.size() - result.size();
                logger.trace("Filtered " + numberFiltered + " auto configuration class in " + TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime) + " ms");
            }

            return new ArrayList(result);
        }
    }

    protected List<AutoConfigurationImportFilter> getAutoConfigurationImportFilters() {
        return SpringFactoriesLoader.loadFactories(AutoConfigurationImportFilter.class, this.beanClassLoader);
    }

    protected final <T> List<T> removeDuplicates(List<T> list) {
        return new ArrayList(new LinkedHashSet(list));
    }

    protected final List<String> asList(AnnotationAttributes attributes, String name) {
        String[] value = attributes.getStringArray(name);
        return Arrays.asList(value);
    }

    private void fireAutoConfigurationImportEvents(List<String> configurations, Set<String> exclusions) {
        List<AutoConfigurationImportListener> listeners = this.getAutoConfigurationImportListeners();
        if (!listeners.isEmpty()) {
            AutoConfigurationImportEvent event = new AutoConfigurationImportEvent(this, configurations, exclusions);
            Iterator var5 = listeners.iterator();

            while(var5.hasNext()) {
                AutoConfigurationImportListener listener = (AutoConfigurationImportListener)var5.next();
                this.invokeAwareMethods(listener);
                listener.onAutoConfigurationImportEvent(event);
            }
        }

    }

    protected List<AutoConfigurationImportListener> getAutoConfigurationImportListeners() {
        return SpringFactoriesLoader.loadFactories(AutoConfigurationImportListener.class, this.beanClassLoader);
    }

    private void invokeAwareMethods(Object instance) {
        if (instance instanceof Aware) {
            if (instance instanceof BeanClassLoaderAware) {
                ((BeanClassLoaderAware)instance).setBeanClassLoader(this.beanClassLoader);
            }

            if (instance instanceof BeanFactoryAware) {
                ((BeanFactoryAware)instance).setBeanFactory(this.beanFactory);
            }

            if (instance instanceof EnvironmentAware) {
                ((EnvironmentAware)instance).setEnvironment(this.environment);
            }

            if (instance instanceof ResourceLoaderAware) {
                ((ResourceLoaderAware)instance).setResourceLoader(this.resourceLoader);
            }
        }

    }

    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        Assert.isInstanceOf(ConfigurableListableBeanFactory.class, beanFactory);
        this.beanFactory = (ConfigurableListableBeanFactory)beanFactory;
    }

    protected final ConfigurableListableBeanFactory getBeanFactory() {
        return this.beanFactory;
    }

    public void setBeanClassLoader(ClassLoader classLoader) {
        this.beanClassLoader = classLoader;
    }

    protected ClassLoader getBeanClassLoader() {
        return this.beanClassLoader;
    }

    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }

    protected final Environment getEnvironment() {
        return this.environment;
    }

    public void setResourceLoader(ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
    }

    protected final ResourceLoader getResourceLoader() {
        return this.resourceLoader;
    }

    public int getOrder() {
        return 2147483646;
    }

    protected static class AutoConfigurationEntry {
        private final List<String> configurations;
        private final Set<String> exclusions;

        private AutoConfigurationEntry() {
            this.configurations = Collections.emptyList();
            this.exclusions = Collections.emptySet();
        }

        AutoConfigurationEntry(Collection<String> configurations, Collection<String> exclusions) {
            this.configurations = new ArrayList(configurations);
            this.exclusions = new HashSet(exclusions);
        }

        public List<String> getConfigurations() {
            return this.configurations;
        }

        public Set<String> getExclusions() {
            return this.exclusions;
        }
    }

    private static class AutoConfigurationGroup implements Group, BeanClassLoaderAware, BeanFactoryAware, ResourceLoaderAware {
        private final Map<String, AnnotationMetadata> entries = new LinkedHashMap();
        private final List<AutoConfigurationImportSelector.AutoConfigurationEntry> autoConfigurationEntries = new ArrayList();
        private ClassLoader beanClassLoader;
        private BeanFactory beanFactory;
        private ResourceLoader resourceLoader;
        private AutoConfigurationMetadata autoConfigurationMetadata;

        private AutoConfigurationGroup() {
        }

        public void setBeanClassLoader(ClassLoader classLoader) {
            this.beanClassLoader = classLoader;
        }

        public void setBeanFactory(BeanFactory beanFactory) {
            this.beanFactory = beanFactory;
        }

        public void setResourceLoader(ResourceLoader resourceLoader) {
            this.resourceLoader = resourceLoader;
        }

        public void process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector) {
            Assert.state(deferredImportSelector instanceof AutoConfigurationImportSelector, () -> {
                return String.format("Only %s implementations are supported, got %s", AutoConfigurationImportSelector.class.getSimpleName(), deferredImportSelector.getClass().getName());
            });
            AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector)deferredImportSelector).getAutoConfigurationEntry(this.getAutoConfigurationMetadata(), annotationMetadata);
            this.autoConfigurationEntries.add(autoConfigurationEntry);
            Iterator var4 = autoConfigurationEntry.getConfigurations().iterator();

            while(var4.hasNext()) {
                String importClassName = (String)var4.next();
                this.entries.putIfAbsent(importClassName, annotationMetadata);
            }

        }

        public Iterable<Entry> selectImports() {
            if (this.autoConfigurationEntries.isEmpty()) {
                return Collections.emptyList();
            } else {
                Set<String> allExclusions = (Set)this.autoConfigurationEntries.stream().map(AutoConfigurationImportSelector.AutoConfigurationEntry::getExclusions).flatMap(Collection::stream).collect(Collectors.toSet());
                Set<String> processedConfigurations = (Set)this.autoConfigurationEntries.stream().map(AutoConfigurationImportSelector.AutoConfigurationEntry::getConfigurations).flatMap(Collection::stream).collect(Collectors.toCollection(LinkedHashSet::new));
                processedConfigurations.removeAll(allExclusions);
                return (Iterable)this.sortAutoConfigurations(processedConfigurations, this.getAutoConfigurationMetadata()).stream().map((importClassName) -> {
                    return new Entry((AnnotationMetadata)this.entries.get(importClassName), importClassName);
                }).collect(Collectors.toList());
            }
        }

        private AutoConfigurationMetadata getAutoConfigurationMetadata() {
            if (this.autoConfigurationMetadata == null) {
                this.autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);
            }

            return this.autoConfigurationMetadata;
        }

        private List<String> sortAutoConfigurations(Set<String> configurations, AutoConfigurationMetadata autoConfigurationMetadata) {
            return (new AutoConfigurationSorter(this.getMetadataReaderFactory(), autoConfigurationMetadata)).getInPriorityOrder(configurations);
        }

        private MetadataReaderFactory getMetadataReaderFactory() {
            try {
                return (MetadataReaderFactory)this.beanFactory.getBean("org.springframework.boot.autoconfigure.internalCachingMetadataReaderFactory", MetadataReaderFactory.class);
            } catch (NoSuchBeanDefinitionException var2) {
                return new CachingMetadataReaderFactory(this.resourceLoader);
            }
        }
    }
}

selectImports方法

public String[] selectImports(AnnotationMetadata annotationMetadata) {
        if (!this.isEnabled(annotationMetadata)) {
            return NO_IMPORTS;
        } else {
            AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);
            AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = this.getAutoConfigurationEntry(autoConfigurationMetadata, annotationMetadata);
            return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
        }
    }

执行此方法时，向spring ioc容器注入bean

selectImports，返回bean全名

import将bean全名注入

注入的bean都是什么

点getAutoConfigurationEntry进去

protected AutoConfigurationImportSelector.AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata, AnnotationMetadata annotationMetadata) {
        if (!this.isEnabled(annotationMetadata)) {
            return EMPTY_ENTRY;
        } else {
            AnnotationAttributes attributes = this.getAttributes(annotationMetadata);
            List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes);
            configurations = this.removeDuplicates(configurations);
            Set<String> exclusions = this.getExclusions(annotationMetadata, attributes);
            this.checkExcludedClasses(configurations, exclusions);
            configurations.removeAll(exclusions);
            configurations = this.filter(configurations, autoConfigurationMetadata);
            this.fireAutoConfigurationImportEvents(configurations, exclusions);
            return new AutoConfigurationImportSelector.AutoConfigurationEntry(configurations, exclusions);
        }
    }

点getCandidateConfigurations进去

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
    List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader());
    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;
}

点SpringFactoriesLoader进去

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package org.springframework.core.io.support;

import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Map.Entry;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.core.io.UrlResource;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.ConcurrentReferenceHashMap;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.StringUtils;

public final class SpringFactoriesLoader {
    public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
    private static final Log logger = LogFactory.getLog(SpringFactoriesLoader.class);
    private static final Map<ClassLoader, MultiValueMap<String, String>> cache = new ConcurrentReferenceHashMap();

    private SpringFactoriesLoader() {
    }

    public static <T> List<T> loadFactories(Class<T> factoryType, @Nullable ClassLoader classLoader) {
        Assert.notNull(factoryType, "'factoryType' must not be null");
        ClassLoader classLoaderToUse = classLoader;
        if (classLoader == null) {
            classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
        }

        List<String> factoryImplementationNames = loadFactoryNames(factoryType, classLoaderToUse);
        if (logger.isTraceEnabled()) {
            logger.trace("Loaded [" + factoryType.getName() + "] names: " + factoryImplementationNames);
        }

        List<T> result = new ArrayList(factoryImplementationNames.size());
        Iterator var5 = factoryImplementationNames.iterator();

        while(var5.hasNext()) {
            String factoryImplementationName = (String)var5.next();
            result.add(instantiateFactory(factoryImplementationName, factoryType, classLoaderToUse));
        }

        AnnotationAwareOrderComparator.sort(result);
        return result;
    }

    public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
        String factoryTypeName = factoryType.getName();
        return (List)loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());
    }

    private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
        MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
        if (result != null) {
            return result;
        } else {
            try {
                Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
                LinkedMultiValueMap result = new LinkedMultiValueMap();

                while(urls.hasMoreElements()) {
                    URL url = (URL)urls.nextElement();
                    UrlResource resource = new UrlResource(url);
                    Properties properties = PropertiesLoaderUtils.loadProperties(resource);
                    Iterator var6 = properties.entrySet().iterator();

                    while(var6.hasNext()) {
                        Entry<?, ?> entry = (Entry)var6.next();
                        String factoryTypeName = ((String)entry.getKey()).trim();
                        String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
                        int var10 = var9.length;

                        for(int var11 = 0; var11 < var10; ++var11) {
                            String factoryImplementationName = var9[var11];
                            result.add(factoryTypeName, factoryImplementationName.trim());
                        }
                    }
                }

                cache.put(classLoader, result);
                return result;
            } catch (IOException var13) {
                throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);
            }
        }
    }

    private static <T> T instantiateFactory(String factoryImplementationName, Class<T> factoryType, ClassLoader classLoader) {
        try {
            Class<?> factoryImplementationClass = ClassUtils.forName(factoryImplementationName, classLoader);
            if (!factoryType.isAssignableFrom(factoryImplementationClass)) {
                throw new IllegalArgumentException("Class [" + factoryImplementationName + "] is not assignable to factory type [" + factoryType.getName() + "]");
            } else {
                return ReflectionUtils.accessibleConstructor(factoryImplementationClass, new Class[0]).newInstance();
            }
        } catch (Throwable var4) {
            throw new IllegalArgumentException("Unable to instantiate factory class [" + factoryImplementationName + "] for factory type [" + factoryType.getName() + "]", var4);
        }
    }
}

发现一个常量：FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";

所有外在的jar包都是通过对应jar包下的这个路径加载配置并实例化的