Spring Boot入门--Spring Boot自动配置原理

Spring Boot在进行SpringApplication对象实例化时会加载META-INF/spring.factories文件,将该配置文件中的配置载入到Spring容器 。

源码分析

  1. 首先,查看org.springframework.boot.SpringApplicationinitialize方法

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    @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();
    }
  2. 其次,查看initialize方法中的getSpringFactoriesInstances方法

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    private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) {
    return getSpringFactoriesInstances(type, new Class<?>[] {});
    }
  3. 接着,查看getSpringFactoriesInstances中的getSpringFactoriesInstances方法

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    private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,
    Class<?>[] parameterTypes, Object... args) {
    ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
    // Use names and ensure unique to protect against duplicates
    Set<String> names = new LinkedHashSet<String>(
    SpringFactoriesLoader.loadFactoryNames(type, classLoader));
    List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
    classLoader, args, names);
    AnnotationAwareOrderComparator.sort(instances);
    return instances;
    }
  4. 最后,查看上面方法中的loadFactoryNames方法

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    public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
    String factoryClassName = factoryClass.getName();
    try {
    Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
    ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
    List<String> result = new ArrayList<String>();
    while (urls.hasMoreElements()) {
    URL url = urls.nextElement();
    Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
    String factoryClassNames = properties.getProperty(factoryClassName);
    result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
    }
    return result;
    }
    catch (IOException ex) {
    throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +
    "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
    }
    }
  5. 查看FACTORIES_RESOURCE_LOCATION可知,这正是前文中谈到的配置文件

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    public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
  6. spring.factories文件内容如下

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    # Initializers
    org.springframework.context.ApplicationContextInitializer=\
    org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
    org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer
    # Application Listeners
    org.springframework.context.ApplicationListener=\
    org.springframework.boot.autoconfigure.BackgroundPreinitializer
    # Auto Configuration Import Listeners
    org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\
    org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener
    # Auto Configuration Import Filters
    org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
    org.springframework.boot.autoconfigure.condition.OnClassCondition
    # Auto Configure
    org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
    org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
    org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
    org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
    org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
    org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
    org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
    org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\
    org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
    org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
    org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
    org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\
    org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.ldap.LdapDataAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\
    org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\
    org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\
    org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
    org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\
    org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\
    org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\
    org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\
    org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\
    org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\
    org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\
    org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\
    org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
    org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\
    org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\
    org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\
    org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\
    org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\
    org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\
    org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\
    org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\
    org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\
    org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
    org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
    org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
    org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
    org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
    org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\
    org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\
    org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\
    org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\
    org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\
    org.springframework.boot.autoconfigure.mobile.DeviceResolverAutoConfiguration,\
    org.springframework.boot.autoconfigure.mobile.DeviceDelegatingViewResolverAutoConfiguration,\
    org.springframework.boot.autoconfigure.mobile.SitePreferenceAutoConfiguration,\
    org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
    org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
    org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
    org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
    org.springframework.boot.autoconfigure.reactor.ReactorAutoConfiguration,\
    org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration,\
    org.springframework.boot.autoconfigure.security.SecurityFilterAutoConfiguration,\
    org.springframework.boot.autoconfigure.security.FallbackWebSecurityAutoConfiguration,\
    org.springframework.boot.autoconfigure.security.oauth2.OAuth2AutoConfiguration,\
    org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
    org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
    org.springframework.boot.autoconfigure.social.SocialWebAutoConfiguration,\
    org.springframework.boot.autoconfigure.social.FacebookAutoConfiguration,\
    org.springframework.boot.autoconfigure.social.LinkedInAutoConfiguration,\
    org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration,\
    org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
    org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
    org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\
    org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
    org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
    org.springframework.boot.autoconfigure.web.DispatcherServletAutoConfiguration,\
    org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration,\
    org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,\
    org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\
    org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\
    org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\
    org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,\
    org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration,\
    org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\
    org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration,\
    org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration,\
    org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration
    # Failure analyzers
    org.springframework.boot.diagnostics.FailureAnalyzer=\
    org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\
    org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\
    org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer
    # Template availability providers
    org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\
    org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\
    org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\
    org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\
    org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\
    org.springframework.boot.autoconfigure.web.JspTemplateAvailabilityProvider
  7. 当程序加载完该配置文件并解析之后,就能够实现自动配置了

Redis自动配置

spring.factories文件中可以看出:
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration是Redis的自动配置

其部分代码如下

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public class RedisAutoConfiguration {
/**
* Redis connection configuration.
*/
@Configuration
@ConditionalOnClass(GenericObjectPool.class)
protected static class RedisConnectionConfiguration {
private final RedisProperties properties;
private final RedisSentinelConfiguration sentinelConfiguration;
private final RedisClusterConfiguration clusterConfiguration;
public RedisConnectionConfiguration(RedisProperties properties,
ObjectProvider<RedisSentinelConfiguration> sentinelConfiguration,
ObjectProvider<RedisClusterConfiguration> clusterConfiguration) {
this.properties = properties;
this.sentinelConfiguration = sentinelConfiguration.getIfAvailable();
this.clusterConfiguration = clusterConfiguration.getIfAvailable();
}
}

详细了解一下RedisProperties

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* Copyright 2012-2016 the original author or authors.
package org.springframework.boot.autoconfigure.data.redis;
import java.util.List;
import org.springframework.boot.context.properties.ConfigurationProperties;
/**
* Configuration properties for Redis.
*
* @author Dave Syer
* @author Christoph Strobl
* @author Marco Aust
*/
@ConfigurationProperties(prefix = "spring.redis")
public class RedisProperties {
/**
* Database index used by the connection factory.
*/
private int database = 0;
/**
* Redis url, which will overrule host, port and password if set.
*/
private String url;
/**
* Redis server host.
*/
private String host = "localhost";
/**
* Login password of the redis server.
*/
private String password;
/**
* Redis server port.
*/
private int port = 6379;
/**
* Enable SSL.
*/
private boolean ssl;
/**
* Connection timeout in milliseconds.
*/
private int timeout;
private Pool pool;
private Sentinel sentinel;
private Cluster cluster;
public int getDatabase() {
return this.database;
}
public void setDatabase(int database) {
this.database = database;
}
public String getUrl() {
return this.url;
}
public void setUrl(String url) {
this.url = url;
}
public String getHost() {
return this.host;
}
public void setHost(String host) {
this.host = host;
}
public String getPassword() {
return this.password;
}
public void setPassword(String password) {
this.password = password;
}
public int getPort() {
return this.port;
}
public void setPort(int port) {
this.port = port;
}
public boolean isSsl() {
return this.ssl;
}
public void setSsl(boolean ssl) {
this.ssl = ssl;
}
public void setTimeout(int timeout) {
this.timeout = timeout;
}
public int getTimeout() {
return this.timeout;
}
public Sentinel getSentinel() {
return this.sentinel;
}
public void setSentinel(Sentinel sentinel) {
this.sentinel = sentinel;
}
public Pool getPool() {
return this.pool;
}
public void setPool(Pool pool) {
this.pool = pool;
}
public Cluster getCluster() {
return this.cluster;
}
public void setCluster(Cluster cluster) {
this.cluster = cluster;
}
/**
* Pool properties.
*/
public static class Pool {
/**
* Max number of "idle" connections in the pool. Use a negative value to indicate
* an unlimited number of idle connections.
*/
private int maxIdle = 8;
/**
* Target for the minimum number of idle connections to maintain in the pool. This
* setting only has an effect if it is positive.
*/
private int minIdle = 0;
/**
* Max number of connections that can be allocated by the pool at a given time.
* Use a negative value for no limit.
*/
private int maxActive = 8;
/**
* Maximum amount of time (in milliseconds) a connection allocation should block
* before throwing an exception when the pool is exhausted. Use a negative value
* to block indefinitely.
*/
private int maxWait = -1;
public int getMaxIdle() {
return this.maxIdle;
}
public void setMaxIdle(int maxIdle) {
this.maxIdle = maxIdle;
}
public int getMinIdle() {
return this.minIdle;
}
public void setMinIdle(int minIdle) {
this.minIdle = minIdle;
}
public int getMaxActive() {
return this.maxActive;
}
public void setMaxActive(int maxActive) {
this.maxActive = maxActive;
}
public int getMaxWait() {
return this.maxWait;
}
public void setMaxWait(int maxWait) {
this.maxWait = maxWait;
}
}
/**
* Cluster properties.
*/
public static class Cluster {
/**
* Comma-separated list of "host:port" pairs to bootstrap from. This represents an
* "initial" list of cluster nodes and is required to have at least one entry.
*/
private List<String> nodes;
/**
* Maximum number of redirects to follow when executing commands across the
* cluster.
*/
private Integer maxRedirects;
public List<String> getNodes() {
return this.nodes;
}
public void setNodes(List<String> nodes) {
this.nodes = nodes;
}
public Integer getMaxRedirects() {
return this.maxRedirects;
}
public void setMaxRedirects(Integer maxRedirects) {
this.maxRedirects = maxRedirects;
}
}
/**
* Redis sentinel properties.
*/
public static class Sentinel {
/**
* Name of Redis server.
*/
private String master;
/**
* Comma-separated list of host:port pairs.
*/
private String nodes;
public String getMaster() {
return this.master;
}
public void setMaster(String master) {
this.master = master;
}
public String getNodes() {
return this.nodes;
}
public void setNodes(String nodes) {
this.nodes = nodes;
}
}
}

可以看到,通过该代码可以读取全局配置文件,获得Redis的相关配置信息

总结

Spring Boot通过代码读取META-INF/spring.factories文件的配置信息,通过将该配置文件中的配置载入到Spring容器并实例化,实现其自动配置功能。