我已经安装了MYSQL服务器5.1。然后我安装了 mysql-connector-java-3.0.8-stable-bin.jar 并将其放入驱动器 c 中,文件夹 core 为 C:\core 。然后在计算机的属性中,我创建带有变量名 CLASSPATH 和变量值的用户变量:C:\core\mysql-connector-java-3.0.8-stable-bin.jar。
现在我已经创建了数据库 EMPLOYEE4
我的java代码是:
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.logging.Level;
import java.util.logging.Logger;
class MySQLTest{
public static void main(String[] args) {
try {
Class.forName("com.mysql.jdbc.Driver");
Connection dbcon = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/EMPLOYEE", "root", "root");
String query ="select count(*) from EMPLOYEE4 ";
Connection dbCon = null;
Statement stmt = null;
ResultSet rs = null;
//getting PreparedStatment to execute query
stmt = dbCon.prepareStatement(query);
//Resultset returned by query
rs = stmt.executeQuery(query);
while(rs.next()){
int count = rs.getInt(1);
System.out.println("count of stock : " + count);
}
} catch (Exception ex) {
ex.printStackTrace();
//Logger.getLogger(CollectionTest.class.getName()).log(Level.SEVERE, null, ex);
} finally{
//close connection ,stmt and resultset here
}
}
}
我收到错误 java.sql.SQLEXCEPTION:通信链接失败:java.IO.Exception 根本原因:输入流意外结束
你应该得到 NPE。当您执行查询时dbCon
并且不在dbcon
// initialize here
Connection dbcon = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/EMPLOYEE", "root", "root");
String query ="select count(*) from EMPLOYEE4 ";
// Null here
Connection dbCon = null;
// on dbCon which is null
stmt = dbCon.prepareStatement(query);
EDIT
这就是你的代码的样子。
Connection dbcon = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/EMPLOYEE", "root", "root");
String query = "select count(*) from EMPLOYEE4 ";
Statement stmt = dbcon.createStatement();
ResultSet rs = stmt.executeQuery(query);
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