您的位置:首页 > 编程语言 > Java开发

SpringBoot自动注入分析

2019-10-17 18:43 1121 查看

  我们经常会被问到这么一个问题:SpringBoot相对于spring有哪些优势呢?其中有一条答案就是SpringBoot自动注入。那么自动注入的原理是什么呢?我们进行如下分析。

  1:首先我们分析项目的启动类时,发现都会加上@SpringBootApplication这个注解,我们分析这个继续进入这个注解会发现,它是由多个注解组成的,如下

@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 {
View Code

  2:服务启动会扫描 org.springframework.boot.autoconfigure下的 META-INF/spring.factories 这个文件,这个文件中保存着springboot 启动时默认会自动注入的类,部分如下

# 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
View Code

  3:你是不是在其中发现了自己常用的redis,mysql等相关的类?没错,springboot会尝试加载这些类,我们以 org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration 这个类为例,进去看一下它的源码,部分示例如下

@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());
}
View Code

  我们能看到这个类上加了这个注解 @ConditionalOnClass({ JedisConnection.class, RedisOperations.class, Jedis.class }) 意思就是如果你的classpath中没有这些类的话,那么这个类就不能被加载,那么这些被依赖的类在哪出现呢?没错,就在我们在pom.xml中引入的依赖所对应的包里。

  看到这里你因该就明白了,META-INF/spring.factories 文件中被列出来的那些类都会被springboot去尝试加载,但是有些模块我们没引入相关的依赖,那么这个类就会加载失败。即这个模块没有被成功加载。

  4:我们通过上面的redis的自动加载类时,看到上面还有个 @EnableConfigurationProperties(RedisProperties.class) 注解,这个注解来注入关于redis的配置信息,这个信息都在 RedisProperties.class 中保存,我们看下 RedisProperties的源码

@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;
}

}

}
View Code

  发现里面的配置项基本都是有默认值的,通过上面的注解可以明白,如果配置文件中存在 spring.redis 开头的配置项,则使用配置文件中的,如果没有的话则使用文件中默认写死的配置。你是不是想到了springboot的另外一个优势:约定大于配置。

  这里我们大概了解了SpringBoot自动配置的原理和流程,里面的那些细节我们不在分析。由此,我们总结出以下几点

  1:SpringBoot的自动配置是如何实现的

  2:有关的那些注解,如@EnableAutoConfiguration, @ConditionalOnClass, @Configuration等也是SpringBoot的核心注解,也值得我们了解其用法和原理。

 

内容来自用户分享和网络整理,不保证内容的准确性,如有侵权内容,可联系管理员处理 点击这里给我发消息
标签: