JDBC 连接失败，错误：与主机的 TCP/IP 连接失败

我想将Java类文件与SQL Server 2012连接。我已使用 SQL Server 身份验证登录，但在连接时收到错误。

错误：

与主机 127.0.0.1 端口 1433 的 TCP/IP 连接失败。错误：“连接被拒绝：连接。验证连接属性。确保 SQL Server 实例在主机上运行，并在端口上接受 TCP/IP 连接。确保与端口的 TCP 连接未被防火墙阻止。

我的代码：

Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");  //1. Register your driver
//2. get the connection object
//Connection con = DriverManager.getConnection("jdbc:sqlserver://localhost;databaseName=aysha","sa","admin");
Connection con = DriverManager.getConnection("jdbc:sqlserver://127.0.0.1;databaseName=aysha","user=sa","password=admin");
 //"jdbc:sqlserver://127.0.0.1:1433; Instance=SQL2008;" +       "databaseName=MB;user=sa;password=123;";
//Connection con = DriverManager.getConnection("jdbc:sqlserver://localhost:1433;databaseName=aysha","sa" , "password");
//3. Prepare a statement
Statement stmt = con.createStatement();
//4. Write the query`
String sql = "Select * from employee";
//5. Execute the statement and 
ResultSet rs = stmt.executeQuery(sql);
//6. Process the result set

while (rs.next())
{
    System.out.println(rs.getInt(1));
}