之前我们在讲解Spring Boot核心注解、配置的时候提到过，Spring Boot的核心注解@SpringBootApplication，会开启“自动配置”，此时Spring Boot会根据项目中配置的jar包依赖，自动做出配置（如自动配置Tomcat容器(包括端口)、dispatcherServlet等MVC组件加载信息，Web.xml文件等）。
那么，Spring Boot的自动配置是如何实现的呢？我们下面通过剖析源码了解一下。
其实Spring boot自动加载的原理一句话就可以说明：
Spring Boot在进行SpringBootApplication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。那么这个“META-INF/spring.factories”在哪呢？我们去原来的样例工程中找到引入的Maven依赖中的“spring-boot-xxx.jar”
在该依赖中，最后的META-INF文件夹下，就是我们的spring.factories文件：
打开该文件，我们可以看到以下内容：
# PropertySource Loaders
org.springframework.boot.env.PropertySourceLoader=\
org.springframework.boot.env.PropertiesPropertySourceLoader,\
org.springframework.boot.env.YamlPropertySourceLoader
# Run Listeners
org.springframework.boot.SpringApplicationRunListener=\
org.springframework.boot.context.event.EventPublishingRunListener
# Application Context Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\
org.springframework.boot.context.ContextIdApplicationContextInitializer,\
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\
org.springframework.boot.context.embedded.ServerPortInfoApplicationContextInitializer
# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.context.FileEncodingApplicationListener,\
org.springframework.boot.context.config.AnsiOutputApplicationListener,\
org.springframework.boot.context.config.ConfigFileApplicationListener,\
org.springframework.boot.context.config.DelegatingApplicationListener,\
org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener,\
org.springframework.boot.logging.ClasspathLoggingApplicationListener,\
org.springframework.boot.logging.LoggingApplicationListener
# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor
# Failure Analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.ConnectorStartFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer
# FailureAnalysisReporters
org.springframework.boot.diagnostics.FailureAnalysisReporter=\
org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter可以看到有许多的配置内容，例如“org.springframework.boot.SpringApplicationRunListener”就是就是Spring Boot的监听器，“org.springframework.context.ApplicationContextInitializer”是Spring容器的初始化对象。总的来说，spring.factories文件提供了很多核心的配置类的类名，Spring Boot在启动的时候，就会加载这些类名，使用类加载器进行类的实例的创建。那么spring.factories文件是什么时候进行加载的呢？我们在样例工程类中使用了SpringApplication类：
package cn.springboot.test;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
//Sprnig Boot项目的核心注解，主要目的是开启自动配置
public class SpringbootTestSimpleApplication {
//该main方法作为项目启动的入口
public static void main(String[] args) {
SpringApplication.run(SpringbootTestSimpleApplication.class, args);
}
}打开SpringApplication类的源码，我们可以找到一个名为“initialize”的初始化方法，该方法会set一些初始化的实例：
@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();
}其中的getSpringFactoriesInstances获取实例的方法：
private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) {
return getSpringFactoriesInstances(Class<T> type,new Class<?>[] {});
}然后getSpringFactoriesInstances(Class<T> type,new Class<?>[] {})方法如下：
private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
LinkedHashSet names = new LinkedHashSet(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
List instances = this.createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances);
return instances;
}其中使用ClassLoader类加载器进行初始化类加载的时候，设置要加载的初始化类的名称使用的是LinkedHashSet，而这些名称的来源就是“SpringFactoriesLoader.loadFactoryNames(type, classLoader)”，找到SpringFactoriesLoader的loadFactoryNames方法:
private static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
private static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
Enumeration<URL> urls = classLoader.getResources(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);
}
}我们可以观察到这么一段代码：
Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);而其中的FACTORIES_RESOURCE_LOCATION即：
private static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";即是我们会读取”META-INF/spring.factories”下配置的类名，将这些类名的路径加载出来，以便于类加载器ClassLoader将对应的类转化为实例对象。上面的是Spring Boot的核心配置，Spring Boot默认会开启了自动配置（因为SpringApplication类的源码中包含@EnableAutoConfiguration注解），我们在样例工程的maven依赖找到“spring-boot-autoconfigure-xxx.jar”：
然后打开它，可以发现在META-INF下面也有spring.factories文件：
在该spring.factories文件下，罗列了自动配置需要加载的各种类路径名：
# 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可以看到里面有aop、数据库、缓存、视图模板等各种自动化配置类路径，spring boot会加载这些自动化配置类，使其实例化，而这些自动化配置类就会帮我们自动进行一系列的默认配置。
例如redis的自动配置，我们在上面的文件中可以找到自动配置类：
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\在“RedisAutoConfiguration”类的源码中我们可以看到：
package org.springframework.boot.autoconfigure.data.redis;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.List;
import org.apache.commons.pool2.impl.GenericObjectPool;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPoolConfig;
import org.springframework.beans.factory.ObjectProvider;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.data.redis.RedisProperties.Cluster;
import org.springframework.boot.autoconfigure.data.redis.RedisProperties.Sentinel;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.redis.connection.RedisClusterConfiguration;
import org.springframework.data.redis.connection.RedisConnectionFactory;
import org.springframework.data.redis.connection.RedisNode;
import org.springframework.data.redis.connection.RedisSentinelConfiguration;
import org.springframework.data.redis.connection.jedis.JedisConnection;
import org.springframework.data.redis.connection.jedis.JedisConnectionFactory;
import org.springframework.data.redis.core.RedisOperations;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;
@Configuration
@ConditionalOnClass({ JedisConnection.class, RedisOperations.class, Jedis.class })
@EnableConfigurationProperties(RedisProperties.class)
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();
}
@Bean
@ConditionalOnMissingBean(RedisConnectionFactory.class)
public JedisConnectionFactory redisConnectionFactory()
throws UnknownHostException {
return applyProperties(createJedisConnectionFactory());
}
protected final JedisConnectionFactory applyProperties(
JedisConnectionFactory factory) {
configureConnection(factory);
if (this.properties.isSsl()) {
factory.setUseSsl(true);
}
factory.setDatabase(this.properties.getDatabase());
if (this.properties.getTimeout() > 0) {
factory.setTimeout(this.properties.getTimeout());
}
return factory;
}
private void configureConnection(JedisConnectionFactory factory) {
if (StringUtils.hasText(this.properties.getUrl())) {
configureConnectionFromUrl(factory);
}
else {
factory.setHostName(this.properties.getHost());
factory.setPort(this.properties.getPort());
if (this.properties.getPassword() != null) {
factory.setPassword(this.properties.getPassword());
}
}
}
private void configureConnectionFromUrl(JedisConnectionFactory factory) {
String url = this.properties.getUrl();
if (url.startsWith("rediss://")) {
factory.setUseSsl(true);
}
try {
URI uri = new URI(url);
factory.setHostName(uri.getHost());
factory.setPort(uri.getPort());
if (uri.getUserInfo() != null) {
String password = uri.getUserInfo();
int index = password.lastIndexOf(":");
if (index >= 0) {
password = password.substring(index + 1);
}
factory.setPassword(password);
}
}
catch (URISyntaxException ex) {
throw new IllegalArgumentException("Malformed 'spring.redis.url' " + url,
ex);
}
}
protected final RedisSentinelConfiguration getSentinelConfig() {
if (this.sentinelConfiguration != null) {
return this.sentinelConfiguration;
}
Sentinel sentinelProperties = this.properties.getSentinel();
if (sentinelProperties != null) {
RedisSentinelConfiguration config = new RedisSentinelConfiguration();
config.master(sentinelProperties.getMaster());
config.setSentinels(createSentinels(sentinelProperties));
return config;
}
return null;
}
/**
* Create a {@link RedisClusterConfiguration} if necessary.
* @return {@literal null} if no cluster settings are set.
*/
protected final RedisClusterConfiguration getClusterConfiguration() {
if (this.clusterConfiguration != null) {
return this.clusterConfiguration;
}
if (this.properties.getCluster() == null) {
return null;
}
Cluster clusterProperties = this.properties.getCluster();
RedisClusterConfiguration config = new RedisClusterConfiguration(
clusterProperties.getNodes());
if (clusterProperties.getMaxRedirects() != null) {
config.setMaxRedirects(clusterProperties.getMaxRedirects());
}
return config;
}
private List<RedisNode> createSentinels(Sentinel sentinel) {
List<RedisNode> nodes = new ArrayList<RedisNode>();
for (String node : StringUtils
.commaDelimitedListToStringArray(sentinel.getNodes())) {
try {
String[] parts = StringUtils.split(node, ":");
Assert.state(parts.length == 2, "Must be defined as 'host:port'");
nodes.add(new RedisNode(parts[0], Integer.valueOf(parts[1])));
}
catch (RuntimeException ex) {
throw new IllegalStateException(
"Invalid redis sentinel " + "property '" + node + "'", ex);
}
}
return nodes;
}
private JedisConnectionFactory createJedisConnectionFactory() {
JedisPoolConfig poolConfig = this.properties.getPool() != null
? jedisPoolConfig() : new JedisPoolConfig();
if (getSentinelConfig() != null) {
return new JedisConnectionFactory(getSentinelConfig(), poolConfig);
}
if (getClusterConfiguration() != null) {
return new JedisConnectionFactory(getClusterConfiguration(), poolConfig);
}
return new JedisConnectionFactory(poolConfig);
}
private JedisPoolConfig jedisPoolConfig() {
JedisPoolConfig config = new JedisPoolConfig();
RedisProperties.Pool props = this.properties.getPool();
config.setMaxTotal(props.getMaxActive());
config.setMaxIdle(props.getMaxIdle());
config.setMinIdle(props.getMinIdle());
config.setMaxWaitMillis(props.getMaxWait());
return config;
}
}
/**
* Standard Redis configuration.
*/
@Configuration
protected static class RedisConfiguration {
@Bean
@ConditionalOnMissingBean(name = "redisTemplate")
public RedisTemplate<Object, Object> redisTemplate(
RedisConnectionFactory redisConnectionFactory)
throws UnknownHostException {
RedisTemplate<Object, Object> template = new RedisTemplate<Object, Object>();
template.setConnectionFactory(redisConnectionFactory);
return template;
}
@Bean
@ConditionalOnMissingBean(StringRedisTemplate.class)
public StringRedisTemplate stringRedisTemplate(
RedisConnectionFactory redisConnectionFactory)
throws UnknownHostException {
StringRedisTemplate template = new StringRedisTemplate();
template.setConnectionFactory(redisConnectionFactory);
return template;
}
}
}实际上RedisAutoConfiguration就是帮我们自动做了一些列的配置，我们在开发中只需要修改少量配置指向自己的redis服务地址即可。
其中：
@ConditionalOnClass({ JedisConnection.class, RedisOperations.class, Jedis.class })表示在容器中如果有JedisConnection.class、RedisOperations.class、Jedis.class这三个指定的Bean时，才会加载RedisAutoConfiguration，否则不进行自动加载。在RedisProperties类中，加载的是redis的各种默认配置信息(主机地址、端口号、密码等信息)：
package org.springframework.boot.autoconfigure.data.redis;
import java.util.List;
import org.springframework.boot.context.properties.ConfigurationProperties;
@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;
}
}
}如果我们在application.properties或application.yml中设置了“spring.redis.*”的相关配置，那么我们自定义的设置就会覆盖原来的自动配置。
“spring.redis.*”在application.properties的相关配置如下：
# REDIS (RedisProperties)
spring.redis.cluster.max-redirects= # Maximum number of redirects to follow when executing commands across the cluster.
spring.redis.cluster.nodes= # Comma-separated list of "host:port" pairs to bootstrap from.
spring.redis.database=0 # Database index used by the connection factory.
spring.redis.url= # Connection URL, will override host, port and password (user will be ignored), e.g. redis://user:password@example.com:6379
spring.redis.host=localhost # Redis server host.
spring.redis.password= # Login password of the redis server.
spring.redis.ssl=false # Enable SSL support.
spring.redis.pool.max-active=8 # Max number of connections that can be allocated by the pool at a given time. Use a negative value for no limit.
spring.redis.pool.max-idle=8 # Max number of "idle" connections in the pool. Use a negative value to indicate an unlimited number of idle connections.
spring.redis.pool.max-wait=-1 # 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.
spring.redis.pool.min-idle=0 # Target for the minimum number of idle connections to maintain in the pool. This setting only has an effect if it is positive.
spring.redis.port=6379 # Redis server port.
spring.redis.sentinel.master= # Name of Redis server.
spring.redis.sentinel.nodes= # Comma-separated list of host:port pairs.
spring.redis.timeout=0 # Connection timeout in milliseconds.这里我们就彻底能了解自动配置的原理，以及我们的配置是如何被加载的了。
补充：
刚刚在Redis 类源码中我们提到@ConditionalOnClass这个注解，根据容器中是否有指定Bean的条件来进行自身加载的判定，这一类型的注解被称为“条件注解”。
常用的“条件注解”如下：
参考：
《JavaEE 开发的颠覆者 Spring Boot实战》 汪云飞编著
传智播客《Spring Boot实战与原理分析》视频课程
(https://pan.baidu.com/s/1o9M2bGI 密码：jxg8)
转载请注明出处：https://blog.csdn.net/acmman/article/details/81975407
