statement执行参数化的sql语句查不出结果

Question

软件环境：eclipse

数据库：oracle 11.1.0*

package nantian.com.loginServlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class loginServlet extends HttpServlet{

    public void doPost(HttpServletRequest req,HttpServletResponse res)
	throws ServletException,IOException{
		
       String username = req.getParameter("username");
	String password = req.getParameter("password");	
	
       Connection connection = null; 
	PreparedStatement statement = null;
       ResultSet resultset = null;
	PrintWriter out = res.getWriter();
		
	try {
	    Class.forName("oracle.jdbc.driver.OracleDriver");
	    String url = "jdbc:oracle:thin:@localhost:1521:orcl";
	    String user = "kflearn";
	    String password2 = "kflearn";
	    connection = DriverManager.getConnection(url, user, password2);
			
	    //此语句能查处结果
/*	    String sql = "select count(user_id) from manager_user where user_name = 'ntyzzhi'" +
	    " and user_pass= '12345' ";*/
	    //这一条执行成功。
/*	    String sql = "select count(user_id) from manager_user where user_name ='"+ username +
	    "' and user_pass='" + password + "'";	*/
	    //这条语句查不出结果，为何？？
	    String sql = "select count(user_id) from manager_user where user_name = ?" + " and user_pass= ? ";	
	
	    statement = connection.prepareStatement(sql);
	    //username 和 password值是 “ntyzzhi” 、”12345“ 查不出，为何？？？？
	    statement.setString(1,"ntyzzhi");
	    statement.setString(2,"12345");
			
	    resultset = statement.executeQuery();
	    System.out.println(sql);
	    if(resultset.next()){
	        int count = resultset.getInt(1);
		System.out.println(count);
		if(count > 0){
		    out.print("hello : " + username);
		}else{
		    out.print("soryy : " + username);
		}
	    }
	} catch (Exception e) {
		e.printStackTrace();
	}finally{
			try {
				if (resultset != null) {
					resultset.close();
				}
			} catch (Exception e2) {
				e2.printStackTrace();
			}
			try {
				if (statement != null) {
					statement.close();
				}
			} catch (Exception e2) {
				e2.printStackTrace();
			}
			try {
				if (connection != null) {
					connection.close();
				}
			} catch (Exception e2) {
				e2.printStackTrace();
			}
		}
	}
}

Answer 1

恩，好的，我再优化一下，谢谢您！

Answer 2

改善一下finally 中的if (xx != null) 判断：将 try catch 放在 if 判断里面

Answer 3

引用来自“yong230”的评论

肯定查不出啊，刚学java吧，字符串类型都得加单引号的

Answer 4

是啊，初学的，这个单引号怎么添加呢？还请您给我写以下，我现在不知道怎么添加！谢谢您！

Answer 5

我已经找到问题了，是因为我数据库里面的字段类型是char类型，是存入的值有空格，所以查询不出。使用语句查询的时候可能会去掉空格。

Answer 6

肯定查不出啊，刚学java吧，字符串类型都得加单引号的