有谁知道为什么当我从 MyServ2 类调用 getResultSet() 方法时出现空指针错误
这是我的 DBClass(省略导入等)
public DBClass(){
}
public Connection dbConnect(String db_connect_string,
String db_userid, String db_password)
{
try
{
DriverManager.registerDriver(new oracle.jdbc.OracleDriver());
conn = DriverManager.getConnection(
db_connect_string, db_userid, db_password);
return conn;
}
catch (Exception e)
{
e.printStackTrace();
return null;
}
}
public ResultSet getResultSet(String query){
try{
stmt = conn.createStatement();
result = stmt.executeQuery(query);
} catch(Exception e){
e.printStackTrace();
return null;
}
return result;
}
}
这是我的 MyServ2 类
public class MyServ2 extends HttpServlet {
private static final long serialVersionUID = 1L;
private DBClass db;
public MyServ2() {
super();
db = new DBClass();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
ResultSet rs = db.getResultSet("Select * from ....ect");
try {
while(rs.next()){
System.out.println(rs.getString(1).toString());
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
最佳答案
您没有调用db.dbConnect()，因此db.conn将为空。
关于Java 空指针，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/4285231/