項(xiàng)目上線一段時(shí)間后，多個(gè)環(huán)境經(jīng)常出現(xiàn)com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure錯(cuò)誤，堆棧信息如下：
The last packet successfully received from the server was 10,003 milliseconds ago. The last packet sent successfully to the server was 10,003 milliseconds ago.
at com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174)
at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64)
at com.mysql.cj.jdbc.StatementImpl.executeQuery(StatementImpl.java:1200)
at com.alibaba.druid.pool.vendor.MySqlValidConnectionChecker.isValidConnection(MySqlValidConnectionChecker.java:140)
at com.alibaba.druid.pool.DruidAbstractDataSource.validateConnection(DruidAbstractDataSource.java:1440)
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1812)
at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2877)
Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure

The last packet successfully received from the server was 10,003 milliseconds ago. The last packet sent successfully to the server was 10,003 milliseconds ago.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:105)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:151)
at com.mysql.cj.exceptions.ExceptionFactory.createCommunicationsException(ExceptionFactory.java:167)
at com.mysql.cj.protocol.a.NativeProtocol.readMessage(NativeProtocol.java:538)
at com.mysql.cj.protocol.a.NativeProtocol.checkErrorMessage(NativeProtocol.java:702)
at com.mysql.cj.protocol.a.NativeProtocol.sendCommand(NativeProtocol.java:641)
at com.mysql.cj.protocol.a.NativeProtocol.sendQueryPacket(NativeProtocol.java:940)
at com.mysql.cj.protocol.a.NativeProtocol.sendQueryString(NativeProtocol.java:886)
at com.mysql.cj.NativeSession.execSQL(NativeSession.java:1073)
at com.mysql.cj.jdbc.StatementImpl.executeQuery(StatementImpl.java:1168)
… 4 common frames omitted
Caused by: java.net.SocketTimeoutException: Read timed out
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
at java.net.SocketInputStream.read(SocketInputStream.java:171)
at java.net.SocketInputStream.read(SocketInputStream.java:141)
at sun.security.ssl.SSLSocketInputRecord.read(SSLSocketInputRecord.java:475)
at sun.security.ssl.SSLSocketInputRecord.readHeader(SSLSocketInputRecord.java:469)
at sun.security.ssl.SSLSocketInputRecord.bytesInCompletePacket(SSLSocketInputRecord.java:69)
at sun.security.ssl.SSLSocketImpl.readApplicationRecord(SSLSocketImpl.java:1228)
at sun.security.ssl.SSLSocketImpl.access$300(SSLSocketImpl.java:75)atsun.security.ssl.SSLSocketImpl$AppInputStream.read(SSLSocketImpl.java:915)
at java.io.FilterInputStream.read(FilterInputStream.java:133)
at com.mysql.cj.protocol.FullReadInputStream.readFully(FullReadInputStream.java:64)
at com.mysql.cj.protocol.a.SimplePacketReader.readHeader(SimplePacketReader.java:63)
at com.mysql.cj.protocol.a.SimplePacketReader.readHeader(SimplePacketReader.java:45)
at com.mysql.cj.protocol.a.TimeTrackingPacketReader.readHeader(TimeTrackingPacketReader.java:52)
at com.mysql.cj.protocol.a.TimeTrackingPacketReader.readHeader(TimeTrackingPacketReader.java:41)
at com.mysql.cj.protocol.a.MultiPacketReader.readHeader(MultiPacketReader.java:54)
at com.mysql.cj.protocol.a.MultiPacketReader.readHeader(MultiPacketReader.java:44)
at com.mysql.cj.protocol.a.NativeProtocol.readMessage(NativeProtocol.java:532)
… 10 common frames omitted
經(jīng)過多次排查和測試，終于排查到了原因。
出現(xiàn)問題的原因是因?yàn)槲覀兊捻?xiàng)目需要?jiǎng)討B(tài)配置數(shù)據(jù)源，程序中根據(jù)需要即時(shí)動(dòng)態(tài)創(chuàng)建DruidDataSource，沒有設(shè)置SocketTimeout和ConnectTimeout參數(shù)，默認(rèn)值都是0，有文章說：connectTimeout的默認(rèn)值為0，表示驅(qū)動(dòng)層面不設(shè)置超時(shí)時(shí)間，但這并不意味著不會(huì)超時(shí)，此時(shí)將由操作系統(tǒng)來決定超時(shí)時(shí)間。實(shí)際經(jīng)過測試，當(dāng)SocketTimeout和ConnectTimeout為默認(rèn)值0時(shí)，兩個(gè)超時(shí)時(shí)間可能都為10秒。
測試代碼：

public static void main(String[] args) throws Exception {

    //創(chuàng)建數(shù)據(jù)源
    DruidDataSource druidDataSource = new DruidDataSource();
    druidDataSource.setUrl("jdbc:mysql://127.0.0.1:3306/test?autoReconnect=true&useUnicode=true&characterEncoding=utf8&allowMultiQueries=true&serverTimezone=GMT%2B8");
    druidDataSource.setUsername("admin");
    druidDataSource.setPassword("admin");
    druidDataSource.setDriverClassName("com.mysql.cj.jdbc.Driver");
    String querySql = "SELECT sleep(11)";	//執(zhí)行語句，該行語句的執(zhí)行時(shí)間≥11秒
    druidDataSource.setConnectionErrorRetryAttempts(3);       //失敗后重連次數(shù)
    druidDataSource.setBreakAfterAcquireFailure(true);
    druidDataSource.setMaxWait(30 * 1000);	//保持的最長時(shí)間
    
    // 以下配置自動(dòng)檢測鏈接的可用性
    druidDataSource.setTestWhileIdle(true);	//明確指定檢測空閑鏈接是否可用
    druidDataSource.setValidationQuery("select 1");	//執(zhí)行該SQL來檢測空閑鏈接，如果不配置，實(shí)際不會(huì)執(zhí)行檢測
    //如果鏈接空閑時(shí)長超過60秒則執(zhí)行檢測，周而復(fù)始。如果該時(shí)長少于MySQL數(shù)據(jù)變量：wait_timeout 會(huì)出現(xiàn)鏈接不可用的情況。
    druidDataSource.setTimeBetweenEvictionRunsMillis(60 * 1000);
    
    druidDataSource.setSocketTimeout(20 * 1000);//超時(shí)時(shí)長：20秒，該值要大于執(zhí)行語句的執(zhí)行時(shí)間
    druidDataSource.setConnectTimeout(20 * 1000);//超時(shí)時(shí)長：20秒，該值要大于執(zhí)行語句的執(zhí)行時(shí)間

    List<Map<String, Object>> result = JdbcUtils.executeQuery(druidDataSource, querySql, Lists.newArrayList());
    System.out.println(JSONUtilExt.toJson(result));
}

請注意測試代碼中的這兩行代碼：
druidDataSource.setSocketTimeout(20 * 1000);
druidDataSource.setConnectTimeout(20 * 1000);
當(dāng)我將這兩行代碼中的任意一行代碼注釋掉或兩行代碼都注釋掉時(shí)，都會(huì)出現(xiàn)文章開始的錯(cuò)誤，且錯(cuò)誤日志相同。

分析到此，基本可以確定，程序里出現(xiàn)上面錯(cuò)誤就是因?yàn)镾ocketTimeout和ConnectTimeout沒有設(shè)置，導(dǎo)致操作系統(tǒng)里實(shí)際默認(rèn)的時(shí)間是10秒，而因?yàn)轫?xiàng)目已經(jīng)上線一段時(shí)間，個(gè)別表里數(shù)據(jù)量比較大，所以在執(zhí)行語句時(shí)偶爾會(huì)出現(xiàn)執(zhí)行時(shí)間超過10秒的情況，連接超時(shí)。因此，根據(jù)需要，在創(chuàng)建數(shù)據(jù)源時(shí)，增加設(shè)置SocketTimeout和ConnectTimeout的大小就可以避免再次出現(xiàn)上述錯(cuò)誤。文章來源地址http://www.zghlxwxcb.cn/news/detail-722525.html

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