問(wèn)題描述

就是普通的查詢mysql數(shù)據(jù)庫(kù)的代碼：

錯(cuò)誤棧如下：

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failureThe last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:526) at com.mysql.jdbc.Util.handleNewInstance(Util.java:406) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2209) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:776) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:526) at com.mysql.jdbc.Util.handleNewInstance(Util.java:406) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:352) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:284) at java.sql.DriverManager.getConnection(DriverManager.java:571) at java.sql.DriverManager.getConnection(DriverManager.java:215) at testHttpConnection.util.DBUtil.getConn(DBUtil.java:26) at testHttpConnection.TestMysql.main(TestMysql.java:23)Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failureThe last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:526) at com.mysql.jdbc.Util.handleNewInstance(Util.java:406) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074) at com.mysql.jdbc.MysqlIO.readPacket(MysqlIO.java:675) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1078) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2137) ... 13 moreCaused by: java.net.SocketException: Permission denied: recv failed at java.net.SocketInputStream.socketRead0(Native Method) at java.net.SocketInputStream.read(SocketInputStream.java:152) at java.net.SocketInputStream.read(SocketInputStream.java:122) at com.mysql.jdbc.util.ReadAheadInputStream.fill(ReadAheadInputStream.java:113) at com.mysql.jdbc.util.ReadAheadInputStream.readFromUnderlyingStreamIfNecessary(ReadAheadInputStream.java:160) at com.mysql.jdbc.util.ReadAheadInputStream.read(ReadAheadInputStream.java:188) at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2494) at com.mysql.jdbc.MysqlIO.readPacket(MysqlIO.java:599) ... 15 more

問(wèn)題解答

我來(lái)分享下我之前出現(xiàn)這個(gè)錯(cuò)誤的解決辦法吧，和1樓不一樣：

eclipse中，設(shè)置“Default VM arguments”添加：“-Djava.net.preferIPv4Stack=true”

具體錯(cuò)誤原因嘛，好像是由于jvm中的配置改變，導(dǎo)致jvm無(wú)法通過(guò)網(wǎng)絡(luò)獲取部分信息

這個(gè)應(yīng)該能解決你的問(wèn)題: Communications link failure的解決辦法

使用Connector/J連接MySQL數(shù)據(jù)庫(kù)，程序運(yùn)行較長(zhǎng)時(shí)間后就會(huì)報(bào)以下錯(cuò)誤：Communications link failure，The last packet successfully received from the server was millisecond ago.The last packet successfully sent to the server was millisecond ago。

其中錯(cuò)誤還會(huì)提示你修改wait_timeout或是使用Connector/J的autoReconnect屬性避免該錯(cuò)誤。后來(lái)查了一些資料，才發(fā)現(xiàn)遇到這個(gè)問(wèn)題的人還真不少，大部分都是使用連接池方式時(shí)才會(huì)出現(xiàn)這個(gè)問(wèn)題，短連接應(yīng)該很難出現(xiàn)這個(gè)問(wèn)題。這個(gè)問(wèn)題的原因：MySQL服務(wù)器默認(rèn)的“wait_timeout”是28800秒即8小時(shí)，意味著如果一個(gè)連接的空閑時(shí)間超過(guò)8個(gè)小時(shí)，MySQL將自動(dòng)斷開(kāi)該連接，而連接池卻認(rèn)為該連接還是有效的(因?yàn)椴⑽葱ｒ?yàn)連接的有效性)，當(dāng)應(yīng)用申請(qǐng)使用該連接時(shí)，就會(huì)導(dǎo)致上面的報(bào)錯(cuò)。修改MySQL的參數(shù)，wait_timeout最大為31536000即1年，在my.cnf中加入：[mysqld]wait_timeout=31536000interactive_timeout=31536000重啟生效，需要同時(shí)修改這兩個(gè)參數(shù)。