hikari中用到的SPI思想

SPI

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 2020/08/23   Share

写在前面

之前文章也说到了SPI最常见的就是JDBC，刚好现在用的就是springboot中的hikari，来看看他是怎么运用SPI思想加载特定的数据库驱动的。

正文

第一次看hikari源码，可以有这么个思路来跟踪源码：

①，找到我们最熟悉的配置中心里配置的DataSourceType，一步找到数据源，②然后找到数据源里的getConnection方法。③并且找到类里的driveClass属性，④找到它的set方法，打上断点，⑤启动项目，开始跟踪吧~,如下图

DataSourceType

debug

继续：

断点启动，跟踪调用栈可以看到springboot初始化配置hikari的地方

debug

//org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration.Hikari
@ConditionalOnClass(HikariDataSource.class)
@ConditionalOnProperty(name = "spring.datasource.type", havingValue = "com.zaxxer.hikari.HikariDataSource", matchIfMissing = true)
static class Hikari extends DataSourceConfiguration {
	
   @Bean
   @ConfigurationProperties(prefix = "spring.datasource.hikari")
   public HikariDataSource dataSource(DataSourceProperties properties) {
     //根据配置创建数据源，即HikariDataSource
      HikariDataSource dataSource = createDataSource(properties,
            HikariDataSource.class);
      if (StringUtils.hasText(properties.getName())) {
         dataSource.setPoolName(properties.getName());
      }
      return dataSource;
   }

}
//一步步走，最终走到我们需要的地方
//com.zaxxer.hikari.HikariConfig#setDriverClassName
//可以看到，这里并没有用spi组件，而是借用了spi的思想
public void setDriverClassName(String driverClassName) {
        if (this.sealed) {
            throw new IllegalStateException("The configuration of the pool is sealed once started.  Use HikariConfigMXBean for runtime changes.");
        } else {
            Class<?> driverClass = null;
          //获取当前的ClassLoader
            ClassLoader threadContextClassLoader = Thread.currentThread().getContextClassLoader();

            try {
                if (threadContextClassLoader != null) {
                    try {
                        driverClass = threadContextClassLoader.loadClass(driverClassName);
                        LOGGER.debug("Driver class {} found in Thread context class loader {}", driverClassName, threadContextClassLoader);
                    } catch (ClassNotFoundException var6) {
                        LOGGER.debug("Driver class {} not found in Thread context class loader {}, trying classloader {}", new Object[]{driverClassName, threadContextClassLoader, this.getClass().getClassLoader()});
                    }
                }

                if (driverClass == null) {
                    driverClass = this.getClass().getClassLoader().loadClass(driverClassName);
                    LOGGER.debug("Driver class {} found in the HikariConfig class classloader {}", driverClassName, this.getClass().getClassLoader());
                }
            } catch (ClassNotFoundException var7) {
                LOGGER.error("Failed to load driver class {} from HikariConfig class classloader {}", driverClassName, this.getClass().getClassLoader());
            }

            if (driverClass == null) {
                throw new RuntimeException("Failed to load driver class " + driverClassName + " in either of HikariConfig class loader or Thread context classloader");
            } else {
                try {
                    driverClass.newInstance();
                    this.driverClassName = driverClassName;
                } catch (Exception var5) {
                    throw new RuntimeException("Failed to instantiate class " + driverClassName, var5);
                }
            }
        }
    }