[strong]java项目案例分析 第五章 学生成绩管理系统   
连接的错误信息提示
一、com.microsoft.sqlserver.jdbc.SQLServerException: 通过端口 1433 连接到主机 localhost 的 TCP/IP 连接失败。错误:“Connection refused: connect。请验证连接属性，并检查 SQL Server 的实例正在主机上运行，且在此端口接受 TCP/IP 连接，还要确保防火墙没有阻止到此端口的 TCP 连接。”。
at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDriverError(SQLServerException.java:170)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.connectHelper(SQLServerConnection.java:1049)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.login(SQLServerConnection.java:833)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.connect(SQLServerConnection.java:716)
at com.microsoft.sqlserver.jdbc.SQLServerDriver.connect(SQLServerDriver.java:841)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at appstu.util.CommonaJdbc.getCon(CommonaJdbc.java:17)
at appstu.util.CommonaJdbc.<init>(CommonaJdbc.java:10)
at appstu.AppStu$1.initAndRecLog(AppStu.java:52)
at appstu.AppStu$1.run(AppStu.java:26)
java.lang.NullPointerException
at appstu.AppStu$1.run(AppStu.java:41)
二、针对以上问题定位到行
   1： conection = DriverManager.getConnection("jdbc:sqlserver://localhost:1433;DatabaseName=DB_Student ","sa","1");
  2：   package appstu.util;

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

public class CommonaJdbc {
    public static Connection conection = null;
    
    public CommonaJdbc() {
     [strong] [em]  getCon();
[/em]        [/strong]
    }
    
    private Connection getCon() {
        try {
            Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
            conection = DriverManager.getConnection("jdbc:sqlserver://localhost:1433;DatabaseName=DB_Student ","sa","1");
        } catch (java.lang.ClassNotFoundException classnotfound) {
            classnotfound.printStackTrace();
        } catch (java.sql.SQLException sql) {
            new appstu.view.JF_view_error(sql.getMessage());
            sql.printStackTrace();
        }
        return conection;
    }
}
             
  3：public class AppStu ---》 private void initAndRecLog() throws FileNotFoundException {
                    FileOutputStream fop = new FileOutputStream("APPStu.log");
                    PrintStream ps = new PrintStream(fop);
                    System.setOut(ps);
                   [strong][em] CommonaJdbc Jdbc = new CommonaJdbc();
[/em][/strong]                    if (CommonaJdbc.conection != null) {
                        jf_login = new JF_login();
                    }
                    
                }
4：public class AppStu ---》     public void run() {
                    try {
                      [strong][em]  initAndRecLog();[/em]
[/strong]                        // 初始化并记录日志
                        System.out.println("系统正在启动中......");
                        System.out.println("系统启动正常......");
                        System.out.println("进入登录窗体......");
                        fis = new FileInputStream("APPStu.log");
                        
                        scanner = new Scanner(fis);
                        while (scanner.hasNextLine()) {
                            String str = scanner.nextLine();
                            str = "启动信息：" + str;
                            Thread.sleep(400);
                        }
scanner.close();
                        fis.close();
                       [strong][em] jf_login.setVisible(true);
[/em] [/strong]                   } catch (Exception e) {
                        e.printStackTrace();
                    }
                }