在应用集体阿里云测试机，在查问实时输入日志时，看到数据库连贯失败后，服务器始终在重连服务器。开始认为是蒙受反复攻打，前面把服务重启后，就没有呈现始终重连的状况。看以下输入日志：
2022-02-09 11:04:58.896 ERROR 16876 --- [eate-1550991149] com.alibaba.druid.pool.DruidDataSource : create connection SQLException, url: jdbc:mysql://47.98.67,98:1234/test?useSSL=false&characterEncoding=UTF-8&serverTimezone=UTC, errorCode 1045, state 28000
java.sql.SQLException: Access denied for user 'root'@'113.90.123.76' (using password: YES)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129) ~[mysql-connector-java-8.0.16.jar:8.0.16]
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97) ~[mysql-connector-java-8.0.16.jar:8.0.16]
at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122) ~[mysql-connector-java-8.0.16.jar:8.0.16]
at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:835) ~[mysql-connector-java-8.0.16.jar:8.0.16]
at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:455) ~[mysql-connector-java-8.0.16.jar:8.0.16]
at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:240) ~[mysql-connector-java-8.0.16.jar:8.0.16]
at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:199) ~[mysql-connector-java-8.0.16.jar:8.0.16]
at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:156) ~[druid-1.1.10.jar:1.1.10]
at com.alibaba.druid.filter.stat.StatFilter.connection_connect(StatFilter.java:218) ~[druid-1.1.10.jar:1.1.10]
at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:150) ~[druid-1.1.10.jar:1.1.10]
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1560) ~[druid-1.1.10.jar:1.1.10]
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1623) ~[druid-1.1.10.jar:1.1.10]
at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2468) ~[druid-1.1.10.jar:1.1.10] 留神下面始终有 druid 数据库连接池的提醒， 这里就想到可能是 druid 连接池的问题，而后去掉 druid maven 依赖后在申请接口就不会呈现重连的问题。
druid 重连起因
在上图源码找到最初一行 DruidDataSource.java:2468 定位到源码上，CreateConnectionThread 创立连接线程，看一下 CreateConnectionThread 源码：
public class CreateConnectionThread extends Thread {public CreateConnectionThread(String name){super(name);
this.setDaemon(true);
}
public void run() {initedLatch.countDown();
long lastDiscardCount = 0;
int errorCount = 0;
for (;;) {
// addLast
try {lock.lockInterruptibly();
} catch (InterruptedException e2) {break;}
long discardCount = DruidDataSource.this.discardCount;
boolean discardChanged = discardCount - lastDiscardCount > 0;
lastDiscardCount = discardCount;
try {
boolean emptyWait = true;
if (createError != null
&& poolingCount == 0
&& !discardChanged) {emptyWait = false;}
if (emptyWait
&& asyncInit && createCount < initialSize) {emptyWait = false;}
if (emptyWait) {
// 必须存在线程期待，才创立连贯
if (poolingCount >= notEmptyWaitThreadCount //
&& !(keepAlive && activeCount + poolingCount < minIdle)) {empty.await();
}
// 避免创立超过 maxActive 数量的连贯
if (activeCount + poolingCount >= maxActive) {empty.await();
continue;
}
}
} catch (InterruptedException e) {
lastCreateError = e;
lastErrorTimeMillis = System.currentTimeMillis();
if (!closing) {LOG.error("create connection Thread Interrupted, url:" + jdbcUrl, e);
}
break;
} finally {lock.unlock();
}
PhysicalConnectionInfo connection = null;
try {connection = createPhysicalConnection();
setFailContinuous(false);
} catch (SQLException e) {LOG.error("create connection SQLException, url:" + jdbcUrl + ", errorCode" + e.getErrorCode()
+ ", state" + e.getSQLState(), e);
errorCount++;
if (errorCount > connectionErrorRetryAttempts && timeBetweenConnectErrorMillis > 0) {
// fail over retry attempts
setFailContinuous(true);
if (failFast) {lock.lock();
try {notEmpty.signalAll();
} finally {lock.unlock();
}
}
if (breakAfterAcquireFailure) {break;}
try {Thread.sleep(timeBetweenConnectErrorMillis);
} catch (InterruptedException interruptEx) {break;}
}
} catch (RuntimeException e) {LOG.error("create connection RuntimeException", e);
setFailContinuous(true);
continue;
} catch (Error e) {LOG.error("create connection Error", e);
setFailContinuous(true);
break;
}
if (connection == null) {continue;}
boolean result = put(connection);
if (!result) {JdbcUtils.close(connection.getPhysicalConnection());
LOG.info("put physical connection to pool failed.");
}
errorCount = 0; // reset errorCount
}
}
}
这是一个多线程的类，而 run 办法外面设置了没有限度的 for 循环 for (;;) {}, 而日志报错定位的信息:
connection = createPhysicalConnection(); 如果符合条件 errorCount > connectionErrorRetryAttempts && timeBetweenConnectErrorMillis > 0 会再次尝试重连，先看一下这几个参数的含意：
errorCount 谬误次数
在 run 办法初始化时为零，每次连贯失败，会主动加 1
connectionErrorRetryAttempts
连贯谬误重试次数，默认值为 1。
protected int connectionErrorRetryAttempts = 1;timeBetweenConnectErrorMillis
连贯间隔时间，单位毫秒。默认值为 500。
protected volatile long timeBetweenConnectErrorMillis = DEFAULT_TIME_BETWEEN_CONNECT_ERROR_MILLIS;
public static final long DEFAULT_TIME_BETWEEN_CONNECT_ERROR_MILLIS = 500; 咱们在连贯数据库失败后，要不在外面 break 中断，其中有
if (breakAfterAcquireFailure) {break;} 将改 break-after-acquire-failure 设置成 true, 在 application.properties 文件如下配置：
spring.datasource.druid.break-after-acquire-failure=true 如果想多尝试连贯几次，须要设置 connection-error-retry-attempts , 当 errorCount 大于 connectionErrorRetryAttempts 才会进入到 条件内，才会中断循环。在 application.properties 文件如下配置：
spring.datasource.druid.connection-error-retry-attempts=3总结
druid 数据库连贯失败，是因为在应用多线程连贯数据时应用了无限度循环连贯，须要在连贯失败中断连贯，须要设置 break-after-acquire-failure 为 true。设置之后数据库连贯不胜利也不会一直的重试。如果要设置重连次数要设置 connection-error-retry-attempts。
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