java通过ajax访问数据库 传值到前台通过jsp展示echart饼图，报错java.lang.NullPointerException

[Pittttttttt]

public class UserDaoImpl implements UserDao {
	
	@Override
	public User login(User user) {
		Connection con = null;
		PreparedStatement ps = null;
		ResultSet rs = null;
		try {
			con = BaseDao.getCon();
			String sql = "select * from user where name=? and password=? ";
			ps = con.prepareStatement(sql);
			ps.setString(1, user.getName());
			ps.setString(2, user.getPassword());
			rs = ps.executeQuery();
			User users;
			if (rs.next()) {
				users = new User();
				System.out.println();
				users.setId(rs.getInt("id"));
				users.setName(rs.getString("name"));
				users.setPassword(rs.getString("password"));
				users.setEmail(rs.getString("email"));
				users.setPhone(rs.getString("phone"));
				users.setMoney(rs.getString("money"));
				return user;
			} else {
				return null;
			}
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return null;
	}

	@Override
	public boolean register(User user) {
		String sql = "insert into user values(0,?,?,?,?,?) ";
		List<Object> list = new ArrayList<Object>();
		list.add(user.getName());
		list.add(user.getPassword());
		list.add(user.getEmail());
		list.add(user.getPhone());
		list.add(user.getMoney());

		boolean flag = BaseDao.addUpdateDelete(sql, list.toArray());
		if (flag) {
			return true;
		} else {
			return false;
		}
	}
	public ArrayList<User> query()  {
		Connection con = null;
		ArrayList<User> barArr = new ArrayList<User>();
		try {
			PreparedStatement stmt = con.prepareStatement("SELECT * FROM user");
			ResultSet rs = stmt.executeQuery();
			while (rs.next()) {
				User bar = new User();
				bar.setName(rs.getString("name"));
				bar.setMoney(rs.getString("money"));
				barArr.add(bar);
			}
			con.close();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return barArr;
	}
	
}

@WebServlet("/user/userlogin")
public class UserLoginServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doPost(request, response);
	}

	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		User user = new User();
		// 获取login.jsp页面提交的账号和密码
		String name = request.getParameter("name");
		String password = request.getParameter("password");
		String money=request.getParameter("money");
		// 测试数据
		System.out.println(name + " " + password+" "+money);
		// 获取login.jsp页面提交的账号和密码设置到实体类User?
		user.setName(name);
		user.setPassword(password);
		HttpSession session = request.getSession();
		// 引入数据交互层
		UserDao dao = new UserDaoImpl();
		User us = dao.login(user);
		// 测试返回的值
		System.out.println(us);
		if (us != null) {
			session.setAttribute("user", user);
			request.getRequestDispatcher("/index/echarts.jsp").forward(request, response);

			// request.setAttribute("info", "登录成功");
		} else {
			request.setAttribute("info", "登录失败");
			request.getRequestDispatcher("/index/info.jsp").forward(request, response);

		}
		
		UserDaoImpl barDao = new UserDaoImpl();
		ArrayList<User> barArr = barDao.query();
		response.setContentType("text/html; charset=utf-8");
		JSONArray json = JSONArray.fromObject(barArr);
		System.out.println(json.toString());
		PrintWriter writer = response.getWriter();
		writer.println(json);
		writer.flush();
		writer.close();
	}
}

public class BaseDao {

	private static String driver;
	private static String url;
	private static String user;
	private static String password;
	private static String money;

	static {
		driver = ResourceBundle.getBundle("db").getString("driver");
		url = ResourceBundle.getBundle("db").getString("url");
		user = ResourceBundle.getBundle("db").getString("user");
		password = ResourceBundle.getBundle("db").getString("password");
	}

	public static Connection getCon() throws ClassNotFoundException, SQLException {
		Class.forName(driver);
		System.out.println("测试加载数据库成功");
		Connection con = DriverManager.getConnection(url, user, password);
		System.out.println("测试数据库连接成功");
		return con;
	}

	public static void close(Connection con, PreparedStatement ps, ResultSet rs) {
		if (rs != null) {// 关闭
			try {
				rs.close();
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		if (ps != null) {
			try {
				ps.close();
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		if (con != null) {
			try {
				con.close();
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

	public static boolean addUpdateDelete(String sql, Object[] arr) {
		Connection con = null;
		PreparedStatement ps = null;
		try {
			con = BaseDao.getCon();// 第一步 ：连接数据库的操作
			ps = con.prepareStatement(sql);// 第二步：预编译
			// 第三步：设置值
			if (arr != null && arr.length != 0) {
				for (int i = 0; i < arr.length; i++) {
					ps.setObject(i + 1, arr[i]);
				}
			}
			int count = ps.executeUpdate();// 第四步：执行sql语句
			if (count > 0) {
				return true;
			} else {
				return false;
			}
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return false;
	}

}

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta charset="utf-8">
<title>ECharts</title>
<script type="text/javascript" src="../scripts/echarts-all.js"></script>
<script type="text/javascript" src="../scripts/jquery.js"></script>
</head>
<body>
您的用户名是:  ${user.name}
	<div id="myDiv" style="height: 400px"></div>
	<script type="text/javascript">
		function loadData(option) {
			
			$.ajax({
				type : 'post', //传输类型
				async : false, 
				url : 'bar.do', //web.xml中注册的Servlet的url-pattern
				data : {"name":name},
				dataType : 'json', //返回数据形式为json
				
				success : function(result) {
					if (result) {
						option.legend.data = [];
						option.series[0].data=[];
						for (var i = 0; i < result.length; i++) {
							alert(result[i].name+"---"+result[i].money);
							option.legend.data.push(result[i].name);
							option.series[0].data.push({name:result[i].name,value:result[i].money});
						}
						myChart.setOption(option);
					}
				},
				error : function(errorMsg) {
					alert("加载数据失败");
					alert(XMLResponse.responseText);
				}
			});//AJAX
		}//loadData()
		var myChart = echarts.init(document.getElementById('myDiv'));
		var option = {
			    title : {
			        text: '某站点用户访问来源',
			        subtext: '纯属虚构',
			        x:'center'
			    },
			    tooltip : {
			        trigger: 'item',
			        formatter: "{a} {b} : {c} ({d}%)"
			    },
			    legend: {
			        orient: 'vertical',
			        left: 'left',
			        data: []
			    },
			    series : [
			        {
			            name: '访问来源',
			            type: 'pie',
			            radius : '55%',
			            center: ['50%', '60%'],
			            data:[],
			            itemStyle: {
			                emphasis: {
			                    shadowBlur: 10,
			                    shadowOffsetX: 0,
			                    shadowColor: 'rgba(0, 0, 0, 0.5)'
			                }
			            }
			        }
			    ]
			};
		//加载数据到option
		loadData(option);
		//设置option
	</script>
</body>
</html>

数据库可以访问也可以进行登录注册操作。

[Merlyj]

你这报错。行数都对不上。大致看了下除了UserDaoImpl 类中query()方法。 public ArrayList<User> query() { Connection con = null;con被你定义成了null值。 这一句PreparedStatement stmt = con.prepareStatement("SELECT * FROM user");相当于PreparedStatement stmt = null.prepareStatement("SELECT * FROM user");

[hp961218]

打个断点Debug看下,空指针很好解决的

[thinking code]

把错误信息贴出来撒

[软件求生]

userdaoimple74行，你看看参数是否传入。

[qq_41228556]

public ArrayList<User> query() { Connection con = null; 这个方法里。con没获取呀，兄弟