java - 函数类函数没有返回到调用函数的控制器类

Question

我正在从控制器类调用一个函数。函数在另一个类函数中定义。但在执行返回代码之前它给出了错误。（作为调试）它从行modelMap.put("list", arraylist); 它给出异常，nullpointerexception。

控制器.java

@RequestMapping(value = "/index.htm")
    public String getData() throws ClassNotFoundException {
        function obj = new function();
        ModelMap modelMap = null;
        obj.getdata(modelMap);
        return "index";
    }

函数.java

public ModelMap getdata(ModelMap modelMap) throws ClassNotFoundException {
        SqlRowSet srs = null;
        ArrayList arraylist = new ArrayList();
        SimpleDriverDataSource dataSource = new SimpleDriverDataSource();
        dataSource = new connection.connection().getConnection(dataSource);
        JdbcTemplate get = new JdbcTemplate(dataSource);
        //Operation
        String sql = "SELECT * FROM user_info";
        srs = get.queryForRowSet(sql);
        while (srs.next()) {
            pojo obj = new pojo();
            obj.setEmail_id(srs.getString("email_id"));
            obj.setPassword(srs.getString("pwd"));
            arraylist.add(obj);
        }

        modelMap.put("list", arraylist);
        return modelMap;
    }

Answer 1

modelMap是null，这就是你得到的原因NullPointerException。你需要初始化它

ModelMap modelMap = new ModelMap();
obj.getdata(modelMap);