1. java 反射机制构建JDBC查询方法

利用Class.formName("")去获取Class对象、在通过Class对象提供的静态方法、获取类或接口的字段、方法、构造这些成员。

了解了反射的一些基础、个人觉得学习编程应该充分的动起手来。在使用过Hibernate的查询过后、突然觉得普通的JDBC查询对查询结果的封装很是麻烦！

于是仿造它、构建一个简单的JDBC查询。

数据库连接类：


/**
* 数据连接类
* @author star
*
*/ 
public class UtilDao { 
    static Properties properties = null; 
    public UtilDao(){ 
        //读取属性文件 
        properties = new Properties(); 
        java.io.InputStream in = (java.io.InputStream) this.getClass() 
                .getResourceAsStream("/mysqlDB.properties"); 
        try { 
            properties.load(in); 
        } catch (IOException ex) {   
            System.out.println(ex.getMessage()); 
            ex.printStackTrace(); 
        } 
    } 
    public Connection getConn(){ 
        Connection connection = null; 
        try{ 
            Class.forName(properties.getProperty("DBDriver")); 
            connection = DriverManager.getConnection(properties.getProperty("url"),properties.getProperty("name"),properties.getProperty("pass")); 
        }catch (Exception err) { 
            System.out.println("连接ConDB-->getCon()____JDBC错误!"); 
            err.printStackTrace();   
            return null;    
        } 
        return connection; 
    } 
    /**
     * 以下是关闭重载方法
     * @param rs
     * @param st
     * @param cs
     * @param conn
     * @throws SQLException
     */ 
    public void closeAll(ResultSet rs,Statement st ,CallableStatement cs ,Connection conn) throws SQLException{ 
        if(rs!=null){ 
            rs.close(); 
        } 
        if(st!=null){ 
            st.close(); 
        } 
        if(cs!=null){ 
            cs.close(); 
        } 
        if(conn!=null){   
            conn.close(); 
        } 
    } 
    public void closeAll(ResultSet rs,Statement st,Connection conn) throws SQLException{ 
        if(rs!=null){ 
            rs.close(); 
        } 
        if(st!=null){ 
            st.close(); 
        } 
        if(conn!=null){   
            conn.close(); 
        } 
    } 
    public void closeAll(ResultSet rs,PreparedStatement ps,Connection conn) throws SQLException{ 
        if(rs!=null){ 
            rs.close(); 
        } 
        if(ps!=null){ 
            ps.close(); 
        } 
        if(conn!=null){   
            conn.close(); 
        }   
    } 
    public void closeAll(PreparedStatement ps,Connection conn) throws SQLException{ 
        if(ps!=null){ 
            ps.close(); 
        } 
        if(conn!=null){   
            conn.close(); 
        }   
    } 
    public void closeAll(Statement st,Connection conn) throws SQLException{ 
        if(st!=null){ 
            st.close(); 
        } 
        if(conn!=null){   
            conn.close(); 
        }   
    } 
    public void closeAll(Connection conn) throws SQLException{ 
        if(conn!=null){   
            conn.close(); 
        }   
    } 
} 
属性文件：

DBDriver=com.mysql.jdbc.Driver 
url=jdbc\:mysql\://localhost\:3306/db
name=root 
pass=root 
characterEncoding=utf8 

数据层接口：

/**
* 访问数据方法接口
* @author star
*
*/ 
@SuppressWarnings("unchecked") 
public interface IDao<T> { 
    /**
     * 分页查询方法
     * @param objClass 类对象
     * @param sql 查询语句
     * @param params 参数
     * @return 分页数据
     * @throws Exception
     */ 
    public List<T> findList(Object objClass,String sql, List params)throws Exception; 
     
    /**
     * 查询一条数据
     * @param objClass 类对象
     * @param sql 查询语句
     * @param params 参数
     * @return 一条数据信息
     * @throws Exception
     */ 
    public T findInfo(Object objClass,String sql ,List params)throws Exception; 
     
}
 
数据层接口实现：


/**
* 访问数据方法实现类
* @author  star

*/ 
@SuppressWarnings({"unchecked","unused"}) 
public class DaoImpl<T> implements IDao<T> { 
 
    private UtilDao dao = new UtilDao(); 
    private Connection conn = null; 
    private ResultSet rs = null; 
    private PreparedStatement ps = null; 
 
    /*
     * 查询一条数据
     */ 
    public T findInfo(Object objClass,String sql, List params) throws Exception { 
        Class c = objClass.getClass();  
        try{ 
            conn = dao.getConn(); 
            ps = conn.prepareStatement(sql); 
            for (int i = 0; i < params.size(); i++) { 
                if(params.get(i)!=null){ 
                    Object obj = params.get(i); 
                    if(obj.getClass().getName().equals("java.lang.String")){ 
                        ps.setString(i+1, obj.toString()); 
                    }else if(obj.getClass().getName().equals("java.lang.Integer")){ 
                        ps.setInt(i+1, Integer.valueOf(obj.toString())); 
                    }else{ 
                        ps.setObject(i+1, obj);     
                    } 
                } 
            } 
            rs = ps.executeQuery(); 
            Class type = null ; //属性类型 
            if(rs.next()){ 
                objClass = c.newInstance(); 
                List<String> list = Reflect003.getKeys(c); 
                Method method = null; 
                for (int i = 0; i < list.size(); i++) { 
                    String key = list.get(i); 
                    String mName = "set"+key.substring(0,1).toUpperCase()+key.substring(1); 
                    String typeName = c.getDeclaredField(key).getType().getName(); 
                    if(typeName.equals("int")){ 
                        type = int.class; 
                        method = c.getMethod(mName, type); 
                        method.invoke(objClass, rs.getInt(key));   
                    }else if(typeName.equals("java.lang.String")){ 
                        type = java.lang.String.class;    
                        method = c.getMethod(mName, type); 
                        method.invoke(objClass, rs.getString(key));     
                    } 
                } 
            } 
        }catch(Exception e){ 
            System.out.println("访问数据方法实现类findInfo方法出错"); 
            e.printStackTrace();  
        }finally{    
            dao.closeAll(rs,ps,conn); 
        }   
        return (T)objClass;  
    }  
 
    /*
     * 分页查询方法
     */ 
    public List<T> findList(Object objClass,String sql, List params) 
    throws Exception { 
        /*
         * 创建返回值对象
         */ 
        List<Object> info = new ArrayList<Object>();   
        //获得Class对象 
        Class c = objClass.getClass();  
        try{ 
            conn = dao.getConn(); 
            ps = conn.prepareStatement(sql); 
            for (int i = 0; i < params.size(); i++) { 
                if(params.get(i)!=null){ 
                    Object obj = params.get(i); 
                    /*
                     * 判断参数的原始类型
                     * 暂时判断Integer跟String类型
                     */ 
                    if(obj.getClass().getName().equals("java.lang.String")){ 
                        ps.setString(i+1, obj.toString()); 
                    }else if(obj.getClass().getName().equals("java.lang.Integer")){ 
                        ps.setInt(i+1, Integer.valueOf(obj.toString())); 
                    }else{ 
                        ps.setObject(i+1, obj);     
                    } 
                } 
            } 
            rs = ps.executeQuery(); 
            Class type = null ; //属性类型 
            while(rs.next()){ 
                //创建一个实例 
                objClass = c.newInstance(); 
                 
                //获取所有的字段名称 
                List<String> list = Reflect003.getKeys(c); 
                 
                Method method = null;//声明Method对象 
                 
                for (int i = 0; i < list.size(); i++) { 
                    String key = list.get(i); 
                    String mName = getSetMethodName(key); //组装set方法名称 
                    String typeName = c.getDeclaredField(key).getType().getName();  //获取字段类型名称 
                    /*
                     * 判断字段类型
                     */ 
                    if(typeName.equals("int")){ 
                        type = int.class; //赋值属性类型 
                        method = c.getMethod(mName, type); //获得Method实例 
                        method.invoke(objClass, rs.getInt(key));  //调用该set方法 
                    }else if(typeName.equals("java.lang.String")){ 
                        type = java.lang.String.class;    
                        method = c.getMethod(mName, type); 
                        method.invoke(objClass, rs.getString(key));     
                    } 
                } 
                info.add(objClass); 
            }   
        }catch(Exception e){ 
            System.out.println("访问数据方法实现类findList方法出错"); 
            e.printStackTrace(); 
        }finally{ 
            dao.closeAll(rs,ps,conn);   
        } 
        return (List<T>)info;   
    } 
    /**
     * 组装set方法
     * @param columnName 字段名
     * @return
     */ 
    private static String getSetMethodName(String columnName) { 
        return "set" + columnName.substring(0, 1).toUpperCase() 
        + columnName.toLowerCase().substring(1); 
    } 
} 
获取所有字段的方法：


/**
* 获取字段名称类
* @author star
*
*/ 
public class Reflect003 { 
    public static List<String> getKeys(Class<?> c){ 
        List<String> list = new ArrayList<String>(); 
        try{ 
            //根据Class的静态方法获取所以字段名称、不包括继承字段 
            Field[] fs = c.getDeclaredFields(); 
            for (int i = 0; i < fs.length; i++) { 
                list.add(fs[i].getName()); 
            } 
        }catch(Exception e){ 
            e.printStackTrace(); 
        } 
        return list; 
    } 
} 

main测试Test：

public static void main(String[] args) throws Exception { 
        DaoImpl dao = new DaoImpl(); 
        test_user u = new test_user(); 
        String sqlPage = "SELECT * FROM userWHERE id <= "; 
        sqlPage += " (SELECT id FROM user ORDER BY id LIMIT "+(2-1)*20+", 1) "; 
        sqlPage += " ORDER BY id LIMIT 20 " ;  // 
         
        List<test_user> listT = (List<test_user>)dao.findList(u, sqlPage, new ArrayList()); 
        for (int i = 0; i < listT.size(); i++) { 
            test_user user = listT.get(i); 
            System.out.println("名称====："+user.getName()); 
        } 
    }