什么是 DataSource？什么又是 DruidDataSource？

概述

DataSource 翻译过来为数据源，它是 jdk 提供的一个接口，然后只提供了两个 getConnection 方法，分别是无参数和需要传入用户名和密码。所以说它是跟数据库连接有关的东西，可以通过它来获取数据库连接。

public interface DataSource  extends CommonDataSource, Wrapper {/*** <p>Attempts to establish a connection with the data source that* this {@code DataSource} object represents.** @return  a connection to the data source* @exception SQLException if a database access error occurs* @throws java.sql.SQLTimeoutException  when the driver has determined that the* timeout value specified by the {@code setLoginTimeout} method* has been exceeded and has at least tried to cancel the* current database connection attempt*/Connection getConnection() throws SQLException;/*** <p>Attempts to establish a connection with the data source that* this {@code DataSource} object represents.** @param username the database user on whose behalf the connection is*  being made* @param password the user's password* @return  a connection to the data source* @exception SQLException if a database access error occurs* @throws java.sql.SQLTimeoutException  when the driver has determined that the* timeout value specified by the {@code setLoginTimeout} method* has been exceeded and has at least tried to cancel the* current database connection attempt* @since 1.4*/Connection getConnection(String username, String password)throws SQLException;
}

但是这只是一个接口，具体怎么获取到数据库连接，还是由实现它的子类来决定。本文就是来讲一下 DruidDataSource，为什么讲它呢？因为它是阿里写出来的，比较 diao。

DruidDataSource

DruidDataSource 是阿里写出来的一个数据源, 它不仅可以获取数据库连接，还把这些数据库连接管理了起来，也就是所谓的数据库连接池。这样的话，当通过该数据源获取数据库连接的时候，如果数据库连接池里有可以使用的连接，那么就直接返回该连接，就省的每次获取数据库连接都要创建了。

首先看一下怎么使用 DruidDataSource。

// 配置一个 DruidDataSource 实例 bean 交由 Spring 容器管理
@Configuration
public class DataSourceConfig {@Beanpublic DataSource dataSource() {DruidDataSource dataSource = new DruidDataSource();dataSource.setUsername("root");dataSource.setPassword("123456");dataSource.setUrl("jdbc:mysql://localhost:3306/transaction?useSSL=false");dataSource.setDriverClassName("com.mysql.jdbc.Driver");//连接池最小空闲的连接数dataSource.setMinIdle(5);//连接池最大活跃的连接数dataSource.setMaxActive(20);//初始化连接池时创建的连接数dataSource.setInitialSize(10);return dataSource;}
}//测试类
public class DataSourceMain {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(DataSourceConfig.class);//获取 dataSource 实例DataSource dataSource = (DataSource) applicationContext.getBean("dataSource");try {//通过数据源获取数据库连接Connection connection = dataSource.getConnection();Statement statement = connection.createStatement();statement.execute("update AccountInfo set balance = balance + 1 where id = 1");} catch (SQLException throwables) {throwables.printStackTrace();}}
}

从上可以看出，通过数据源访问跟 jdbc 方式相比，省略了实例化数据库连接驱动 Driver 驱动这一步，此外调用 getConnection() 获取连接的时候，并没有传用户名和密码，说明 dataSource 把这些配置信息都管理起来了。后面获取连接的逻辑会自给自足。

总结来说，DruidDataSource 管理了数据库连接的一些配置信息，还帮助我们创建了连接驱动 Driver, 剩下的逻辑就跟 jdbc 一毛一样了。管理配置信息就不说了，无非就是定义一些变量，然后通过 set 方法给写进去。接下来我们开一下什么时候创建的 Driver, 以及怎么获取数据库连接的。

首先进入 DruidDataSource 类的 getConnection() 方法

    public DruidPooledConnection getConnection() throws SQLException {return getConnection(maxWait);}//这个参数代表超时时间，过了这个时间还没有获取到连接就代表获取连接失败。public DruidPooledConnection getConnection(long maxWaitMillis) throws SQLException {//初始化方法init();if (filters.size() > 0) {FilterChainImpl filterChain = new FilterChainImpl(this);return filterChain.dataSource_connect(this, maxWaitMillis);} else {return getConnectionDirect(maxWaitMillis);}}

这里主要有两个方法，第一个是初始化方法，第二个是 getConnectionDirect(maxWaitMillis)，很明显第二个是获取连接的，那么第一个是干什么的？

    public void init() throws SQLException {// inited 控制该初始化方法只调用一次，在方法后面会设置为 true，再次调用该方法就会直接返回。if (inited) {return;}// bug fixed for dead lock, for issue #2980//这一行是为了解决死锁问题，https://github.com/alibaba/druid/issues/2980 详情可以去这个连接看一下DruidDriver.getInstance();final ReentrantLock lock = this.lock;try {lock.lockInterruptibly();} catch (InterruptedException e) {throw new SQLException("interrupt", e);}boolean init = false;try {if (inited) {return;}initStackTrace = Utils.toString(Thread.currentThread().getStackTrace());this.id = DruidDriver.createDataSourceId();if (this.id > 1) {long delta = (this.id - 1) * 100000;this.connectionIdSeedUpdater.addAndGet(this, delta);this.statementIdSeedUpdater.addAndGet(this, delta);this.resultSetIdSeedUpdater.addAndGet(this, delta);this.transactionIdSeedUpdater.addAndGet(this, delta);}if (this.jdbcUrl != null) {this.jdbcUrl = this.jdbcUrl.trim();initFromWrapDriverUrl();}for (Filter filter : filters) {filter.init(this);}if (this.dbType == null || this.dbType.length() == 0) {this.dbType = JdbcUtils.getDbType(jdbcUrl, null);}if (JdbcConstants.MYSQL.equals(this.dbType)|| JdbcConstants.MARIADB.equals(this.dbType)|| JdbcConstants.ALIYUN_ADS.equals(this.dbType)) {boolean cacheServerConfigurationSet = false;if (this.connectProperties.containsKey("cacheServerConfiguration")) {cacheServerConfigurationSet = true;} else if (this.jdbcUrl.indexOf("cacheServerConfiguration") != -1) {cacheServerConfigurationSet = true;}if (cacheServerConfigurationSet) {this.connectProperties.put("cacheServerConfiguration", "true");}}if (maxActive <= 0) {throw new IllegalArgumentException("illegal maxActive " + maxActive);}if (maxActive < minIdle) {throw new IllegalArgumentException("illegal maxActive " + maxActive);}if (getInitialSize() > maxActive) {throw new IllegalArgumentException("illegal initialSize " + this.initialSize + ", maxActive " + maxActive);}if (timeBetweenLogStatsMillis > 0 && useGlobalDataSourceStat) {throw new IllegalArgumentException("timeBetweenLogStatsMillis not support useGlobalDataSourceStat=true");}if (maxEvictableIdleTimeMillis < minEvictableIdleTimeMillis) {throw new SQLException("maxEvictableIdleTimeMillis must be grater than minEvictableIdleTimeMillis");}if (this.driverClass != null) {this.driverClass = driverClass.trim();}initFromSPIServiceLoader();//此时 driver 还没有初始化if (this.driver == null) {if (this.driverClass == null || this.driverClass.isEmpty()) {this.driverClass = JdbcUtils.getDriverClassName(this.jdbcUrl);}if (MockDriver.class.getName().equals(driverClass)) {driver = MockDriver.instance;} else {if (jdbcUrl == null && (driverClass == null || driverClass.length() == 0)) {throw new SQLException("url not set");}// 会调用这个方法获取 driver 实例driver = JdbcUtils.createDriver(driverClassLoader, driverClass);}} else {if (this.driverClass == null) {this.driverClass = driver.getClass().getName();}}initCheck();initExceptionSorter();initValidConnectionChecker();validationQueryCheck();if (isUseGlobalDataSourceStat()) {dataSourceStat = JdbcDataSourceStat.getGlobal();if (dataSourceStat == null) {dataSourceStat = new JdbcDataSourceStat("Global", "Global", this.dbType);JdbcDataSourceStat.setGlobal(dataSourceStat);}if (dataSourceStat.getDbType() == null) {dataSourceStat.setDbType(this.dbType);}} else {dataSourceStat = new JdbcDataSourceStat(this.name, this.jdbcUrl, this.dbType, this.connectProperties);}dataSourceStat.setResetStatEnable(this.resetStatEnable);//初始化数据库连接池，其实就是个数组connections = new DruidConnectionHolder[maxActive];evictConnections = new DruidConnectionHolder[maxActive];keepAliveConnections = new DruidConnectionHolder[maxActive];SQLException connectError = null;if (createScheduler != null && asyncInit) {for (int i = 0; i < initialSize; ++i) {submitCreateTask(true);}} else if (!asyncInit) {// init connections// 这个就是通过配置设置的初始化的连接的个数while (poolingCount < initialSize) {try {// 获取数据库连接PhysicalConnectionInfo pyConnectInfo = createPhysicalConnection();DruidConnectionHolder holder = new DruidConnectionHolder(this, pyConnectInfo);//将获取到的数据库连接放入到连接池中，也就是 connections 数组中connections[poolingCount++] = holder;} catch (SQLException ex) {LOG.error("init datasource error, url: " + this.getUrl(), ex);if (initExceptionThrow) {connectError = ex;break;} else {Thread.sleep(3000);}}}if (poolingCount > 0) {poolingPeak = poolingCount;poolingPeakTime = System.currentTimeMillis();}}createAndLogThread();//创建一个线程负责创建新的数据库连接createAndStartCreatorThread();createAndStartDestroyThread();initedLatch.await();init = true;initedTime = new Date();registerMbean();if (connectError != null && poolingCount == 0) {throw connectError;}if (keepAlive) {// async fill to minIdleif (createScheduler != null) {for (int i = 0; i < minIdle; ++i) {submitCreateTask(true);}} else {this.emptySignal();}}} catch (SQLException e) {LOG.error("{dataSource-" + this.getID() + "} init error", e);throw e;} catch (InterruptedException e) {throw new SQLException(e.getMessage(), e);} catch (RuntimeException e){LOG.error("{dataSource-" + this.getID() + "} init error", e);throw e;} catch (Error e){LOG.error("{dataSource-" + this.getID() + "} init error", e);throw e;} finally {// 设置 inited 为 true，当再次调用 init() 方法的时候就会直接返回。inited = true;lock.unlock();if (init && LOG.isInfoEnabled()) {String msg = "{dataSource-" + this.getID();if (this.name != null && !this.name.isEmpty()) {msg += ",";msg += this.name;}msg += "} inited";LOG.info(msg);}}}

上面的代码量很多，但是我们目前先把目光放到主线代码中，那么很明显有几个重要的点

获取 driver 实例 driver = JdbcUtils.createDriver(driverClassLoader, driverClass);
获取数据库连接 PhysicalConnectionInfo pyConnectInfo = createPhysicalConnection();
此外我们还知道了所谓连接池就是一个数组，它保存着一个个连接对象实例。

首先看下如何获取 driver

 public static Driver createDriver(ClassLoader classLoader, String driverClassName) throws SQLException {Class<?> clazz = null;if (classLoader != null) {try {clazz = classLoader.loadClass(driverClassName);} catch (ClassNotFoundException e) {// skip}}if (clazz == null) {try {ClassLoader contextLoader = Thread.currentThread().getContextClassLoader();if (contextLoader != null) {clazz = contextLoader.loadClass(driverClassName);}} catch (ClassNotFoundException e) {// skip}}if (clazz == null) {try {clazz = Class.forName(driverClassName);} catch (ClassNotFoundException e) {throw new SQLException(e.getMessage(), e);}}try {//通过反射获取实例，其实也就是 jdbc 获取 driverreturn (Driver) clazz.newInstance();} catch (IllegalAccessException e) {throw new SQLException(e.getMessage(), e);} catch (InstantiationException e) {throw new SQLException(e.getMessage(), e);}}

可以看出，它跟使用 jdbc 时一样，都是通过反射获取到 driver 实例，然后我们再看一下如何获取一个连接

public PhysicalConnectionInfo createPhysicalConnection() throws SQLException {String url = this.getUrl();Properties connectProperties = getConnectProperties();String user;if (getUserCallback() != null) {user = getUserCallback().getName();} else {user = getUsername();}String password = getPassword();PasswordCallback passwordCallback = getPasswordCallback();if (passwordCallback != null) {if (passwordCallback instanceof DruidPasswordCallback) {DruidPasswordCallback druidPasswordCallback = (DruidPasswordCallback) passwordCallback;druidPasswordCallback.setUrl(url);druidPasswordCallback.setProperties(connectProperties);}char[] chars = passwordCallback.getPassword();if (chars != null) {password = new String(chars);}}Properties physicalConnectProperties = new Properties();if (connectProperties != null) {physicalConnectProperties.putAll(connectProperties);}if (user != null && user.length() != 0) {physicalConnectProperties.put("user", user);}if (password != null && password.length() != 0) {physicalConnectProperties.put("password", password);}Connection conn = null;long connectStartNanos = System.nanoTime();long connectedNanos, initedNanos, validatedNanos;Map<String, Object> variables = initVariants? new HashMap<String, Object>(): null;Map<String, Object> globalVariables = initGlobalVariants? new HashMap<String, Object>(): null;createStartNanosUpdater.set(this, connectStartNanos);creatingCountUpdater.incrementAndGet(this);try {// 这时physicalConnectProperties已经拼装好了配置信息，也获取到了urlconn = createPhysicalConnection(url, physicalConnectProperties);connectedNanos = System.nanoTime();if (conn == null) {throw new SQLException("connect error, url " + url + ", driverClass " + this.driverClass);}initPhysicalConnection(conn, variables, globalVariables);initedNanos = System.nanoTime();validateConnection(conn);validatedNanos = System.nanoTime();setFailContinuous(false);setCreateError(null);} catch (SQLException ex) {setCreateError(ex);JdbcUtils.close(conn);throw ex;} catch (RuntimeException ex) {setCreateError(ex);JdbcUtils.close(conn);throw ex;} catch (Error ex) {createErrorCountUpdater.incrementAndGet(this);setCreateError(ex);JdbcUtils.close(conn);throw ex;} finally {long nano = System.nanoTime() - connectStartNanos;createTimespan += nano;creatingCountUpdater.decrementAndGet(this);}return new PhysicalConnectionInfo(conn, connectStartNanos, connectedNanos, initedNanos, validatedNanos, variables, globalVariables);}

    public Connection createPhysicalConnection(String url, Properties info) throws SQLException {Connection conn;if (getProxyFilters().size() == 0) {// 这里是获取到我们刚刚实例化的 driver, 然后再调用它的 connect 方法conn = getDriver().connect(url, info);} else {conn = new FilterChainImpl(this).connection_connect(info);}createCountUpdater.incrementAndGet(this);return conn;}

从上可以看出，获取数据库连接首先也是要获取到 driver 然后再调用它的 connect 方法。

总的来说，上面代码的主线逻辑就是先实例化 driver, 然后通过 driver 获取一个数据库连接，这其实也就是 jdbc 的方式，只不过别让帮我们做了这件事情，我们不用再自己做了而已。并且DruidDataSource 在获取到连接之后，还会把这个连接存起来，以免每次请求连接都要重新从数据库获取一个连接。

上一部分讲的是初始化方法 init(), 别忘了我们是讲 DruidDataSource 获取数据库连接方法的，如下

    public DruidPooledConnection getConnection(long maxWaitMillis) throws SQLException {// 执行初始化方法后，这时连接池里已经有了数据库连接了init();if (filters.size() > 0) {FilterChainImpl filterChain = new FilterChainImpl(this);return filterChain.dataSource_connect(this, maxWaitMillis);} else {return getConnectionDirect(maxWaitMillis);}}

我们需要看一下 getConnectionDirect(maxWaitMillis) 是怎么获取连接的

    public DruidPooledConnection getConnectionDirect(long maxWaitMillis) throws SQLException {int notFullTimeoutRetryCnt = 0;for (;;) {// handle notFullTimeoutRetryDruidPooledConnection poolableConnection;try {//很明显这个方法就是获取数据库连接的， 剩下的代码可以先不看，直接跳到getConnectionInternalpoolableConnection = getConnectionInternal(maxWaitMillis);} catch (GetConnectionTimeoutException ex) {if (notFullTimeoutRetryCnt <= this.notFullTimeoutRetryCount && !isFull()) {notFullTimeoutRetryCnt++;if (LOG.isWarnEnabled()) {LOG.warn("get connection timeout retry : " + notFullTimeoutRetryCnt);}continue;}throw ex;}。。。。。。。。。。。//省略下面的代码

private DruidPooledConnection getConnectionInternal(long maxWait) throws SQLException {。。。。。。。。。。//省略该方法前面的一些代码// 等待超时时间，默认是 -1if (maxWait > 0) {holder = pollLast(nanos);} else {holder = takeLast();}if (holder != null) {activeCount++;if (activeCount > activePeak) {activePeak = activeCount;activePeakTime = System.currentTimeMillis();}}} catch (InterruptedException e) {connectErrorCountUpdater.incrementAndGet(this);throw new SQLException(e.getMessage(), e);} catch (SQLException e) {connectErrorCountUpdater.incrementAndGet(this);throw e;} finally {lock.unlock();}break;}DruidPooledConnection poolalbeConnection = new DruidPooledConnection(holder);return poolalbeConnection;}

我们在代码里看到 pollLast 和 takeLast 是获取数据库连接的，这两个方法差不多，pollLast()会加入时间的判断，但是核心逻辑都是一样的，所以我们跟一下默认的 takeLast 方法

DruidConnectionHolder takeLast() throws InterruptedException, SQLException {try {//如果没有设置连接池初始化大小，则会重新创建一个连接放入连接池， 如果设置了初始化大小，则在调用init()方法的时候会创建一些连接放在连接池中保存。while (poolingCount == 0) {emptySignal(); // send signal to CreateThread create connectionif (failFast && isFailContinuous()) {throw new DataSourceNotAvailableException(createError);}notEmptyWaitThreadCount++;if (notEmptyWaitThreadCount > notEmptyWaitThreadPeak) {notEmptyWaitThreadPeak = notEmptyWaitThreadCount;}try {notEmpty.await(); // signal by recycle or creator} finally {notEmptyWaitThreadCount--;}notEmptyWaitCount++;if (!enable) {connectErrorCountUpdater.incrementAndGet(this);if (disableException != null) {throw disableException;}throw new DataSourceDisableException();}}} catch (InterruptedException ie) {notEmpty.signal(); // propagate to non-interrupted threadnotEmptySignalCount++;throw ie;}//将数据库连接池中的连接数减一decrementPoolingCount();//获取数据库连接池中的的一个连接DruidConnectionHolder last = connections[poolingCount];connections[poolingCount] = null;return last;}

通过上面的分析，我们应该已经知道，当调用 Connection connection = dataSource.getConnection() 的时候，如果是第一次调用，则会在 init() 方法的时候创建一些连接放入数据库连接池里，然后获取连接的时候，直接从连接池中获取。

总结

DruidDataSource 博大精深，我只是分析了其中一些基本的功能，还有很多代码没有分析，但是本文的主要目的是为了让大家了解 DataSource 是个啥玩意，我们现在应该知道了它就是管理数据库连接的，如果需要一个连接的话问他要就行了。

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什么是 DataSource？什么又是 DruidDataSource？

概述

DruidDataSource

总结

什么是 DataSource？什么又是 DruidDataSource？相关推荐

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