相关疑难解决方法(0)

我编写了一个Java程序,程序连接到我服务器上的数据库,以查找记录,写入记录,更新和删除.由于某些原因,查找记录有效,但大多数情况下,当我尝试保存或写入记录时,它会显示一条错误消息:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 9,787 milliseconds ago.       The last packet sent successfully to the server was 8,183 milliseconds ago.

Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2552)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3002)
... 46 more

任何人都可以解释为什么会这样吗？在软件运行超过半分钟后,通常这会在尝试添加记录时给出错误消息.似乎松动了连接或什么的.当我运行程序并快速写一个新记录时,它的工作原理

我应该如何添加JAR库在Eclipse中一个WAR项目没有遇到java.lang.ClassNotFoundException或java.lang.NoClassDefFoundError？

在CLASSPATH环境变量似乎并没有工作.在某些情况下,我们将JAR文件添加到Eclipse项目的Build Path属性中以使代码编译.我们有时需要将JAR文件放在/WEB-INF/libJava EE Web应用程序的文件夹中,以使代码在该JAR内的类上运行.

我不完全理解为什么CLASSPATH不起作用,在哪些情况下我们应该将JAR添加到Build Path以及何时应该放置这些JAR /WEB-INF/lib.

我有一个Java类,它通过JDBC访问MySQL数据库,我在Tomcat上运行的JSP中使用,我得到No Driver Found Exception.

我有一个方法:

private static Statement makeStatement() {
   try{
    com.mysql.jdbc.Driver d = null;
    try{d = new com.mysql.jdbc.Driver();}catch(Exception e){
      System.out.println("ERROR BY NEW DRIVER " + e.toString() + 
      "\n");e.printStackTrace();}
    Connection con = DriverManager.getConnection(url, user, password);
    return con.createStatement();
   }catch(java.sql.SQLException ex){
      System.out.println("ERROR IN makeStatement " + "\nERROR - " +
      ex.toString() +  "\n ERROR CODE:\n " + ex.getErrorCode() + 
      "\nSQLSTATE:\n " + ex.getSQLStat        e());ex.printStackTrace();}
    return null;
 }

这引发了一个错误.Connection con = DriverManager.getConnection(url, user, password);这是我的catalina.out打印输出:

  Received Parameters

ERROR IN makeStatement 
ERROR - …

我试图连接到我的远程MySQL数据库,但我失败并得到了这个错误.

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

令人困惑的是,当我使用MySQL-Front工具连接远程数据库时,它是有效的,我可以成功ping到IP地址.但是当我使用我的代码时,它会在大约十秒后显示错误.

此外,当我在我的代码中使用了错误的用户名或密码时,它会立即显示错误的验证.这是否证明设置连接是没有问题的？

这是我的代码(它可以在我的localhost数据库上工作):

public static void main(String[] args) {
        String url = "jdbc:mysql://(IP address):3306/";
        String dbName = "talk";
        String driver = "com.mysql.jdbc.Driver";
        String userName = "talkroot";
        String password = "123456";
        try {
            Class.forName(driver).newInstance();
            Connection conn = DriverManager.getConnection(url + dbName,
                    userName, password);
            System.out.println("connect");
            conn.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println("end");
    }

这是错误:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Last packet sent to the server was 0 ms ago.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown …

我试图连接mysql database但我失败了,显示了这个错误

Communications link failure Last packet sent to the server was 1 ms ago

这是我的代码？任何人都可以帮助我

package android_programmers_guide.testconnection;


import java.sql.Connection;
import java.sql.DriverManager;

import android.os.Bundle;
import android.app.Activity;
import android.graphics.Color;
import android.view.Menu;
import android.widget.EditText;

public class TestConnection extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test_connection);



           Connection conn = null;
           String url = "jdbc:mysql://127.0.0.1:3306/test";
           String driver = "com.mysql.jdbc.Driver";
           String userName = "root"; 
           String password = "root";


           try {
           Class.forName(driver).newInstance();
           conn = DriverManager.getConnection(url,userName,password);


           EditText editText=(EditText) findViewById(R.id.editText1);


           editText.setBackgroundColor(Color.GREEN);
           editText.setText("Connected to …

来自的输出$NIFI_HOME/logs/nifi-app.log：

2016-10-26 12:45:13,304 ERROR [Timer-Driven Process Thread-6] o.apache.nifi.processors.standard.PutSQL
org.apache.nifi.processor.exception.ProcessException: org.apache.commons.dbcp.SQLNestedException: Cannot create JDBC driver of class 'com.mysql.jdbc.Driver' for connect URL 'jdbc:sqlserver://*BLOCKED*/*BLOCKED*'
        at org.apache.nifi.dbcp.DBCPConnectionPool.getConnection(DBCPConnectionPool.java:234) ~[na:na]
        at sun.reflect.GeneratedMethodAccessor393.invoke(Unknown Source) ~[na:na]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_101]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_101]
        at org.apache.nifi.controller.service.StandardControllerServiceProvider$1.invoke(StandardControllerServiceProvider.java:177) ~[nifi-framework-core-1.0.0.jar:1.0.0]
        at com.sun.proxy.$Proxy81.getConnection(Unknown Source) ~[na:na]
        at org.apache.nifi.processors.standard.PutSQL.onTrigger(PutSQL.java:218) ~[na:na]
        at org.apache.nifi.processor.AbstractProcessor.onTrigger(AbstractProcessor.java:27) ~[nifi-api-1.0.0.jar:1.0.0]
        at org.apache.nifi.controller.StandardProcessorNode.onTrigger(StandardProcessorNode.java:1064) ~[nifi-framework-core-1.0.0.jar:1.0.0]
        at org.apache.nifi.controller.tasks.ContinuallyRunProcessorTask.call(ContinuallyRunProcessorTask.java:136) [nifi-framework-core-1.0.0.jar:1.0.0]
        at org.apache.nifi.controller.tasks.ContinuallyRunProcessorTask.call(ContinuallyRunProcessorTask.java:47) [nifi-framework-core-1.0.0.jar:1.0.0]
        at org.apache.nifi.controller.scheduling.TimerDrivenSchedulingAgent$1.run(TimerDrivenSchedulingAgent.java:132) [nifi-framework-core-1.0.0.jar:1.0.0]
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_101]
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [na:1.8.0_101]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_101]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [na:1.8.0_101]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_101]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_101]
        at …

我尝试在家里和Java SDK一起安装它... SDK工作正常,我现在可以使用命令提示符将java程序编译成类...

但是,我不确定如何测试JDBC是否正在连接到我的server/databases/mysql.

我感觉我的服务器(这是一个共享的网站/ webhost)可能不允许连接...

如何测试JDBC是否已正确安装而无需连接到服务器？

然后,我如何测试(请分开代码)(现已确认工作)JDBC连接到我的数据库？

非常感谢.

我编写了这个 java 应用程序来响应来自命令行的数据并将其存储到数据库中：

 import java.util.Scanner;
import java.sql.*;


public class Program {


    public static void main(String[] args)throws ClassNotFoundException 


    {


        Connection conn=null;

        try {

            Class.forName("com.mysql.jdbc.Driver");

             conn = DriverManager.getConnection("jdbc:mysql://localhost/DevOps_DB","root","root");


             PreparedStatement st = conn.prepareStatement("INSERT INTO pers " + "VALUES ('"+args[0]+"'); ");
             st.executeUpdate();


        } 



        catch (SQLException ex) {

            System.out.println("SQL Exception : "+ ex.getMessage());

            System.out.println("Vendor Error : "+ ex.getErrorCode());

        }


        catch(ClassNotFoundException ex) {

            ex.printStackTrace();


        }



//      
//      for(String arg : args)            
//      {   
//           System.out.println(arg);            
//      }




    }





}

但我有以下例外：

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native …

当我运行我的代码时,我得到这个例外:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The 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:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1121)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:357)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2482)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2519)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2304)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
    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:422)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:346)
    at java.sql.DriverManager.getConnection(DriverManager.java:664)
    at java.sql.DriverManager.getConnection(DriverManager.java:208)
    at org.springframework.jdbc.datasource.DriverManagerDataSource.getConnectionFromDriverManager(DriverManagerDataSource.java:153)
    at org.springframework.jdbc.datasource.DriverManagerDataSource.getConnectionFromDriver(DriverManagerDataSource.java:144)
    at org.springframework.jdbc.datasource.AbstractDriverBasedDataSource.getConnectionFromDriver(AbstractDriverBasedDataSource.java:155)
    at org.springframework.jdbc.datasource.AbstractDriverBasedDataSource.getConnection(AbstractDriverBasedDataSource.java:120)
    at …

我正在尝试在docker的帮助下使用kafka debezium（Kafka流）将一个数据库的表数据下沉到另一个数据库。数据库流工作正常。但流式数据接收另一个 MySQL DB 进程时出现错误。

对于我的连接器接收器配置如下。

 {
  "name": "mysql_sink",
  "config": {
    "connector.class": "io.confluent.connect.jdbc.JdbcSinkConnector",
    "topics": "mysql-connect.kafka_test.employee",
    "connection.url": "jdbc:mysql://localhost/kafka_test_1&user=debezium&password=xxxxx",
    "auto.create": "true",
    "auto.evolve": "true",
    "insert.mode": "upsert",
    "pk.fields": "id",
    "pk.mode": "record_value",
    "errors.tolerance": "all",
    "errors.log.enable":"true",
    "errors.log.include.messages":"true",
    "key.converter": "org.apache.kafka.connect.json.JsonConverter",
    "value.converter": "org.apache.kafka.connect.json.JsonConverter",
    "key.converter.schemas.enable": "false",
    "value.converter.schemas.enable": "false",
    "name": "mysql_sink"
  }
}

但我收到错误。

org.apache.kafka.connect.errors.ConnectException: Exiting WorkerSinkTask due to unrecoverable exception.
org.apache.kafka.connect.runtime.WorkerSinkTask.deliverMessages(WorkerSinkTask.java:560)
org.apache.kafka.connect.runtime.WorkerSinkTask.poll(WorkerSinkTask.java:321)
org.apache.kafka.connect.runtime.WorkerSinkTask.iteration(WorkerSinkTask.java:224)
org.apache.kafka.connect.runtime.WorkerSinkTask.execute(WorkerSinkTask.java:192)
org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:175)
org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:219)
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
java.util.concurrent.FutureTask.run(FutureTask.java:266)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
java.lang.Thread.run(Thread.java:748)\nCaused by: org.apache.kafka.connect.errors.ConnectException: java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost/kafka_test_1&user=debezium&password=xxxxx
io.confluent.connect.jdbc.util.CachedConnectionProvider.getValidConnection(CachedConnectionProvider.java:59)
io.confluent.connect.jdbc.sink.JdbcDbWriter.write(JdbcDbWriter.java:52)
io.confluent.connect.jdbc.sink.JdbcSinkTask.put(JdbcSinkTask.java:66)
org.apache.kafka.connect.runtime.WorkerSinkTask.deliverMessages(WorkerSinkTask.java:538)\n\t... 10 more\nCaused by: java.sql.SQLException: No …