将查询结果封装成类的更通用方法

快来打我* 2022-08-09 01:52 158阅读 0赞

前一个实例只是将封装User对象，下面这个例子可以封装Object

package cn.itcast.domain;
    
    import java.lang.reflect.Method;
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.ResultSetMetaData;
    
    import cn.itcast.jdbc.JdbcUtils;
    
    public class ORMTest { 
    
        public static void main(String[] args) throws Exception {
            User user = (User) getObject(
                    "select id as Id , name as Name , birthday as Birthday , money as Money from user where id = 1",
                    User.class);
            System.out.println(user);
        }
    
        static Object getObject(String sql, Class clazz) throws Exception {
            Connection conn = null;
            PreparedStatement ps = null;
            ResultSet rs = null;
    
            try {
                conn = JdbcUtils.getConnection();
                ps = conn.prepareStatement(sql);
                rs = ps.executeQuery();
                ResultSetMetaData rsmd = rs.getMetaData();
                int count = rsmd.getColumnCount();
                String[] colNames = new String[count];
                for (int i = 1; i <= count; i++) {
                    colNames[i - 1] = rsmd.getColumnName(i);
                }
    
                Object object = null;
                Method[] ms = clazz.getMethods();
                while (rs.next()) {
                    object = clazz.newInstance(); // 传进来的Class一定有一个不带参数的构造方法
    
                    for (int i = 0; i < colNames.length; i++) {
                        String colName = colNames[i];
                        String methodName = "set" + colName; // set方法的名字
                        for (Method m : ms) {
                            if (methodName.equals(m.getName()))
                                m.invoke(object, rs.getObject(colName));
                        }
                    }
                }
                return object;
            } finally {
                JdbcUtils.free(rs, ps, conn);
            }
        }
    }