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简介
上文中探索了Alibaba Druid的连接池初始化和获取连接的关键代码，接下来详细看看初始化部分
数据库连接池初始化
对整个代码加上注释，如下：
public void init() throws SQLException {
// 已经初始化过了，直接返回
if (inited) {
return;
}
// bug fixed for dead lock, for issue #2980
DruidDriver.getInstance();
// 初始化时上锁
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());
// 这部分尚不清楚作用
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);
}
// 数据库连接url
if (this.jdbcUrl != null) {
this.jdbcUrl = this.jdbcUrl.trim();
initFromWrapDriverUrl();
}
// filter相关，目前为空
for (Filter filter : filters) {
filter.init(this);
}
// 获取数据库类型
if (this.dbTypeName == null || this.dbTypeName.length() == 0) {
this.dbTypeName = JdbcUtils.getDbType(jdbcUrl, null);
}
// 针对 mysql、mariadb、oceanbase、ads 做其特有的处理
DbType dbType = DbType.of(this.dbTypeName);
if (dbType == DbType.mysql
|| dbType == DbType.mariadb
|| dbType == DbType.oceanbase
|| dbType == DbType.ads) {
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");
}
}
// 下面就是一些配置的效验
// 这部分是不是放到最前面比较好？
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 (keepAlive && keepAliveBetweenTimeMillis <= timeBetweenEvictionRunsMillis) {
throw new SQLException("keepAliveBetweenTimeMillis must be grater than timeBetweenEvictionRunsMillis");
}
// driverClass相关
if (this.driverClass != null) {
this.driverClass = driverClass.trim();
}
// 下面这段有些初始化加载和检查，但不是看的太明白
initFromSPIServiceLoader();
resolveDriver();
initCheck();
initExceptionSorter();
initValidConnectionChecker();
validationQueryCheck();
// Stat 的作用是啥，目前尚不清楚
if (isUseGlobalDataSourceStat()) {
dataSourceStat = JdbcDataSourceStat.getGlobal();
if (dataSourceStat == null) {
dataSourceStat = new JdbcDataSourceStat("Global", "Global", this.dbTypeName);
JdbcDataSourceStat.setGlobal(dataSourceStat);
}
if (dataSourceStat.getDbType() == null) {
dataSourceStat.setDbType(this.dbTypeName);
}
} else {
dataSourceStat = new JdbcDataSourceStat(this.name, this.jdbcUrl, this.dbTypeName, this.connectProperties);
}
dataSourceStat.setResetStatEnable(this.resetStatEnable);
// 关键的数据库连接池相关的，在获取连接中就是从DruidConnectionHolder中获取的
connections = new DruidConnectionHolder[maxActive];
evictConnections = new DruidConnectionHolder[maxActive];
keepAliveConnections = new DruidConnectionHolder[maxActive];
SQLException connectError = null;
// 这段看大致意思的异步去生成数据库物理连接
// 因为else中是可以看出直接获取了数据库的物理连接，然后放到DruidConnectionHolder中
if (createScheduler != null && asyncInit) {
for (int i = 0; i < initialSize; ++i) {
submitCreateTask(true);
}
} else if (!asyncInit) {
// init connections
while (poolingCount < initialSize) {
try {
PhysicalConnectionInfo pyConnectInfo = createPhysicalConnection();
DruidConnectionHolder holder = new DruidConnectionHolder(this, pyConnectInfo);
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();
}
}
// 一些辅助性，日志啥的初始化操作
createAndLogThread();
createAndStartCreatorThread();
createAndStartDestroyThread();
initedLatch.await();
init = true;
initedTime = new Date();
registerMbean();
if (connectError != null && poolingCount == 0) {
throw connectError;
}
// 前面使用的是initialSize 初始连接数
// 这个使用的是 keepAlive 看着意思是空闲连接数
if (keepAlive) {
// async fill to minIdle
if (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 {
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);
}
}
}
总结
从上看出：
- 初始化做了双检查锁
- 数据库可以异步或者同步产生配置的初始连接数
- 如果keepalive为true，异步生成配置的最小空闲连接数
当前只简单的了解了整个初始化过程，但其中还有很多细节，感觉是自己对这个业务场景没有理解到位
