利用反射機制實現簡單數據查詢

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

public class BasicDao {
    private static Connection con = null;
    private static PreparedStatement ps = null;
    private static ResultSet rs = null;
    
    public static <T> List<T> selectAll(Class<T> clazz, String sql, Object parameter) {
        List<T> result = new ArrayList<T>();
        // 遍歷parameter的所有屬性和值作為參數
        Field[] paramField = parameter.getClass().getDeclaredFields();
        for (Field pf : paramField) {
            try {
                if (pf.getType() == String.class) {
                    if (pf.get(parameter) != null) {
                        sql = sql.replace("/*" + pf.getName() + "*/", "'" + pf.get(parameter).toString() + "'");
                    }
                } else {
                    if (pf.get(parameter) != null) {
                        sql = sql.replace("/*" + pf.getName() + "*/", pf.get(parameter).toString());
                    }
                }
                System.out.println(pf.getName() + ":" + pf.get(parameter));
            } catch (IllegalArgumentException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        }
        try {
            con = DBConnection.ConnectDB();
            ps = con.prepareStatement(sql);
            System.out.println("[sql]:" + ps.toString().substring(ps.toString().indexOf(" ")));
            rs = ps.executeQuery();
            while (rs.next()) {
                T entity;
                try {
                    entity = clazz.newInstance();
                } catch (Exception e) {
                    e.printStackTrace();
                    return result;
                }
                Field[] entityFiled = clazz.getFields();
                int fieldCount = 0;
                for (Field ef : entityFiled) {
                    // 根據字段取出對應set方法賦值
                    Method m;
                    try {
                        m = entity.getClass().getMethod(
                                "set" + ef.getName().substring(0, 1).toUpperCase() + ef.getName().substring(1),
                                ef.getType());
                        if (ef.getType() == Integer.class) {
                            m.invoke(entity, rs.getInt(++fieldCount));
                        } else if (ef.getType() == Long.class) {
                            m.invoke(entity, rs.getLong(++fieldCount));
                        } else if (ef.getType() == Double.class) {
                            m.invoke(entity, rs.getDouble(++fieldCount));
                        } else if (ef.getType() == Date.class) {
                            m.invoke(entity, rs.getDate(++fieldCount));
                        } else if (ef.getType() == String.class) {
                            m.invoke(entity, rs.getString(++fieldCount));
                        } // TODO
                    } catch (Exception e) {
                        e.printStackTrace();
                        return result;
                    }
                }
                result.add(entity);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }
}