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

Question

I want my database to communicate with my java programs Can anyone provide me with a sample program using JDBC? I’m getting an error while doing the same Exception in thread "main" 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:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1122) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2260) at com.mysql.jdbc.ConnectionImpl.(ConnectionImpl.java:787) at com.mysql.jdbc.JDBC4Connection.(JDBC4Connection.java:49) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:357) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285) at java.sql.DriverManager.getConnection(DriverManager.java:582) at java.sql.DriverManager.getConnection(DriverManager.java:207) at SqlTest.main(SqlTest.java:22) Caused by: 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:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1122) at com.mysql.jdbc.MysqlIO.(MysqlIO.java:344) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2181) ... 12 more Caused by: java.net.ConnectException: Connection refused at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333) at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195) at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:432) at java.net.Socket.connect(Socket.java:529) at java.net.Socket.connect(Socket.java:478) at java.net.Socket.(Socket.java:375) at java.net.Socket.(Socket.java:218) at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:256) at com.mysql.jdbc.MysqlIO.(MysqlIO.java:293) ... 13 more Contents of my text file are given as follows: import com.mysql.jdbc.*; import java.sql.connectionA; import java.sql.DriverManagerB; import java.sql.PreparedStatementC; import java.sql.ResultSetD; import java.sql.SQLExceptionE; import java.sql.StatementF; public class Test { public static void main(Stringxyz [] args) throws Exception { // Class.forName( "com.mysql.jdbc.DriverWXY" ); // do this in init // // edit the jdbc url connectionA conn = DriverManager.getConnection( "jdbc:mysql://localhost:3306/projects?user=usera&password=12345"); // StatementF F = conn.createStatement(); // ResultSetD D = st.executeQuery( "select * from table" ); System.out.println("Connected or not?"); } Contents of the test file: import com.mysql.jdbc.*; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class SqlTest { public static void main(String [] args) throws Exception { // Class.forName( "com.mysql.jdbc.Driver" ); // do this in init // // edit the jdbc url Connection conn = DriverManager.getConnection( "jdbc:mysql://localhost:3306/projects?user=user1&password=123"); // Statement st = conn.createStatement(); // ResultSet rs = st.executeQuery( "select * from table" ); System.out.println("Connected?"); } } Select the correct answer from above options

Answer 1

Your exception seems to indicate that your MySQL server is not available. Exception in thread “main” com.mysql.exceptions.jdbc4. CommunicationsException: Communication link failure. The last packet sent successfully to the server was 0 milliseconds ago. No packet has been received by the driver from the server. Now, trying from the terminal: Mysql -u username -p You will be asked for the password associated with the username. Does the MySQL client connect after providing the correct password? You might have to start MySQL from the preferences. If not, you can also set it to run at the startup.