Question

我正在尝试使用JDBC为我正在进行的项目连接到一个新数据库，这将允许我输出一整套关于体育游戏的统计数据。但是在尝试连接数据库时遇到了一些麻烦。我在下面收到以下错误。

com.mysql.jdbc.CommunicationsException: Communications link failure due      to underlying exception: 

** BEGIN NESTED EXCEPTION ** 

java.net.ConnectException
MESSAGE: Connection refused

STACKTRACE:

java.net.ConnectException: Connection refused
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at java.net.Socket.connect(Socket.java:538)
at java.net.Socket.<init>(Socket.java:434)
at java.net.Socket.<init>(Socket.java:244)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:256)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:271)
at com.mysql.jdbc.Connection.createNewIO(Connection.java:2771)
at com.mysql.jdbc.Connection.<init>(Connection.java:1555)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:247)
at JDBC.main(JDBC.java:22)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)


** END NESTED EXCEPTION **



Last packet sent to the server was 0 ms ago.
    at com.mysql.jdbc.Connection.createNewIO(Connection.java:2847)
    at com.mysql.jdbc.Connection.<init>(Connection.java:1555)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:247)
at JDBC.main(JDBC.java:22)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

此错误源自我的代码，如下所示：

//STEP 1. Import required packages
import java.sql.*;

public class JDBC {
    // JDBC driver name and database URL
    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
    static final String DB_URL = "jdbc:mysql://localhost/";

    //  Database credentials
    static final String USER = "username";
    static final String PASS = "password";

    public static void main(String[] args) {
        Connection conn = null;
        Statement stmt = null;
        try{
            //STEP 2: Register JDBC driver
            Class.forName("com.mysql.jdbc.Driver");

            //STEP 3: Open a connection
            System.out.println("Connecting to database...");
            conn = DriverManager.getConnection(DB_URL, USER, PASS);

            //STEP 4: Execute a query
            System.out.println("Creating database...");
            stmt = conn.createStatement();

            String sql = "CREATE DATABASE PREDICTOR";
            stmt.executeUpdate(sql);
            System.out.println("Database created successfully...");
        }catch(SQLException se){
            //Handle errors for JDBC
            se.printStackTrace();
        }catch(Exception e){
            //Handle errors for Class.forName
            e.printStackTrace();
        }finally{
            //finally block used to close resources
            try{
                if(stmt!=null)
                    stmt.close();
            }catch(SQLException se2){
            }// nothing we can do
            try{
                if(conn!=null)
                    conn.close();
            }catch(SQLException se){
                se.printStackTrace();
            }//end finally try
        }//end try
        System.out.println("Goodbye!");
    }//end main
}

我已经禁用了我的防火墙并查看了以前关于堆栈溢出的帖子试图修改我的问题但是alas连接被拒绝了。任何帮助表示赞赏。

Answer 1

拒绝连接

这意味着与服务器的TCP通信被主动拒绝 - 这是在TCP层完成的，连接从未进入您的服务 - 此时您的代码无关紧要。

这可能是由几个不同的问题引起的：

SQL服务器实际上并未运行
有阻止连接的防火墙
您正在连接到服务器正在侦听的其他端口。

Answer 2

我认为你的SQL服务器没有运行。请检查服务器状态。或者您应该重新安装服务器。它可以解决你的问题。

Answer 3

您的DB_URL不正确。它应该

DB_URL = "jdbc:mysql://localhost/databaseName";

如果数据库服务器未使用默认端口

，您也可以在网址中使用端口号

DB_URL = "jdbc:mysql://localhost:portNumber/databaseName";

有关详细信息，请访问this site

使用JDBC连接到MYSQL数据库

3 个答案: