今天写ssm的时候遇见一个错误，
我的报错如下
1 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@21ee9275 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: 2 com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure 3 4 The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. 5 at sun.reflect.GeneratedConstructorAccessor23.newInstance(Unknown Source) 6 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) 7 at java.lang.reflect.Constructor.newInstance(Constructor.java:423) 8 at com.mysql.jdbc.Util.handleNewInstance(Util.java:425) 9 at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:990) 10 at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:342) 11 at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2197) 12 at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2230) 13 at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2025) 14 at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:778) 15 at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47) 16 at sun.reflect.GeneratedConstructorAccessor15.newInstance(Unknown Source) 17 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) 18 at java.lang.reflect.Constructor.newInstance(Constructor.java:423) 19 at com.mysql.jdbc.Util.handleNewInstance(Util.java:425) 20 at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:386) 21 at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:330) 22 at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:175) 23 at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220) 24 at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206) 25 at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203) 26 at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138) 27 at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125) 28 at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44) 29 at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870) 30 at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696) 31 Caused by: java.net.ConnectException: Connection refused: connect 32 at java.net.DualStackPlainSocketImpl.connect0(Native Method) 33 at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79) 34 at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350) 35 at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206) 36 at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188) 37 at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172) 38 at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) 39 at java.net.Socket.connect(Socket.java:589) 40 at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:211) 41 at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:301) 42 ... 20 more 43 44 八月 21, 2020 5:01:26 下午 com.mchange.v2.resourcepool.BasicResourcePool 45 警告: Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@520d0d4e is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests. 46 八月 21, 2020 5:01:26 下午 com.mchange.v2.resourcepool.BasicResourcePool 47 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@634f6fcf -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: 48 com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure 49 50 The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. 51 at sun.reflect.GeneratedConstructorAccessor23.newInstance(Unknown Source) 52 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) 53 at java.lang.reflect.Constructor.newInstance(Constructor.java:423) 54 at com.mysql.jdbc.Util.handleNewInstance(Util.java:425) 55 at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:990) 56 at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:342) 57 at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2197) 58 at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2230) 59 at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2025) 60 at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:778) 61 at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47) 62 at sun.reflect.GeneratedConstructorAccessor15.newInstance(Unknown Source) 63 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) 64 at java.lang.reflect.Constructor.newInstance(Constructor.java:423) 65 at com.mysql.jdbc.Util.handleNewInstance(Util.java:425) 66 at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:386) 67 at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:330) 68 at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:175) 69 at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220) 70 at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206) 71 at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203) 72 at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138) 73 at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125) 74 at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44) 75 at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870) 76 at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696) 77 Caused by: java.net.ConnectException: Connection refused: connect 78 at java.net.DualStackPlainSocketImpl.connect0(Native Method) 79 at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79) 80 at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350) 81 at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206) 82 at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188) 83 at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172) 84 at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) 85 at java.net.Socket.connect(Socket.java:589) 86 at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:211) 87 at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:301) 88 ... 20 more 89 90 八月 21, 2020 5:01:26 下午 com.mchange.v2.resourcepool.BasicResourcePool 91 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@6c971fde -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: 92 com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure 93 94 The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. 95 at sun.reflect.GeneratedConstructorAccessor23.newInstance(Unknown Source) 96 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) 97 at java.lang.reflect.Constructor.newInstance(Constructor.java:423) 98 at com.mysql.jdbc.Util.handleNewInstance(Util.java:425) 99 at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:990) 100 at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:342) 101 at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2197) 102 at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2230) 103 at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2025) 104 at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:778) 105 at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47) 106 at sun.reflect.GeneratedConstructorAccessor15.newInstance(Unknown Source) 107 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) 108 at java.lang.reflect.Constructor.newInstance(Constructor.java:423) 109 at com.mysql.jdbc.Util.handleNewInstance(Util.java:425) 110 at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:386) 111 at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:330) 112 at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:175) 113 at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220) 114 at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206) 115 at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203) 116 at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138) 117 at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125) 118 at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44) 119 at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870) 120 at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696) 121 Caused by: java.net.ConnectException: Connection refused: connect 122 at java.net.DualStackPlainSocketImpl.connect0(Native Method) 123 at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79) 124 at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350) 125 at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206) 126 at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188) 127 at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172) 128 at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) 129 at java.net.Socket.connect(Socket.java:589) 130 at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:211) 131 at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:301) 132 ... 20 more
上网查了很多，
有的说是dao层xml条件参数值错误，仔细检查并没有，
有的说是一般有Illegal access: this web application instance has been stopped already. Could not load+....+The eventual following stack trace is caused by+.......这种类型的错误都是因为重新加载失败引起的；
检查各种属性名和参数名都没问题之后，最后打开服务才发现是mysql服务停止，打开就好，其实解决之后发现，报错的提示中含有jdbc几个关键字，不难发现是连接出现错误
希望能给朋友们解决问题
总结，遇到bug不要急，先排除代码问题再看配置，再康康环境，慢慢来，冰冻三尺，非一日之寒