java反射获取类属性问题。

Question

代码：

 public static List<Object> select(String sql, String o)
                throws SQLException, ClassNotFoundException, InstantiationException, IllegalAccessException {
            Class c = Class.forName(o);
            Field[] fls = c.getDeclaredFields();
            List<String> list=  new ArrayList<>();
            for (int i = 0; i < fls.length; i++) {
                System.out.println("公有属性之" + fls[i].getName());
                list.add(fls[i].getName());
            }
            Object object = c.newInstance();
            List<Object> l = new ArrayList<>();
            stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery(sql);
            while (rs.next()) {
                // Retrieve by column name
                String id = rs.getString("href");
               String name = rs.getString("title");      
            // Display values
            System.out.print("ID: " + id);
            System.out.print(", name: " + name);
        }
        rs.close();
        stmt.close();
        conn.close();
        return l;

    }

我想获取传进来的类的所有属性，然后通过re.getString获得值，但是我不知道属性有多少个，在rs.next里for循环遍历的话就会失去rs的作用域。麻烦哪位大神帮我看看怎么写 = =。

Answer 1

I’m not very good at typesetting, so I can just read it.

while(rs.next()){
    //cls: Class<T> cls
    T t=cls.newInstance();
    //rsmd: ResultSetMetaData rsmd
    for(int i=0;i<rsmd.getColumnCount();i++){
        errorIndex=i+1;
        String columnName=(rsmd.getColumnName(i+1)).toLowerCase();
        //rs: ResultSet rs
        Object obj=rs.getObject(columnName);
        if(null==obj) continue;
        columnName=String.valueOf(columnName.charAt(0)).toUpperCase()+columnName.substring(1);
        Method m;
        m=cls.getMethod("set"+columnName, obj.getClass());
        m.invoke(t, obj);
    }
    dataList.add(t);
}

Answer 2

There is actually a problem with your reflection:
Even if you want to get the class object, it is best not to pass Class.formName, unless you really need to dynamically load external classes.

I don’t know if writing like this meets your requirements

public static List<Map<String,Object>> select(Object o)
             throws SQLException, ClassNotFoundException, InstantiationException, IllegalAccessException {
         Field[] fds=o.getClass().getDeclaredFields();
            String[] names=new String[fds.length];
            for(int i=0;i<fds.length;i++){
                names[i]=fds[i].getName();
                System.out.println(names[i]);
            }
        List<Map<String,Object>> list=new ArrayList<>();
         stmt = conn.createStatement();
         ResultSet rs = stmt.executeQuery(sql);
         while (rs.next()) {
             Map<String,Object> m=new HashMap<>();
             for(String name:names){
                 String tmp = rs.getString(name);
                 m.put(name, tmp);
             }
             list.add(m);  
         }
     rs.close();
     stmt.close();
     conn.close();
     return list;

Answer 3

org.springframework.jdbc.core.BeanPropertyRowMapper Ready-made implementation, you can refer to it and imitate it.