基于Java反射实现简易ORM

简易ORM

简介

利用java反射，可以实现一个简易的orm，从此再也不用傻傻的写dao了。。。

目标

实现查询和插入方法。其中查询方法需要接受一个POJO对象，DBUtil会自动根据POJO中已经提供的信息补全sql。例如User对象中已经设置了username属性为omsfuk，则sql会变成：select * from user where username = 'omsfuk'。插入方法类似。

代码

Talk is chaper， show me the code
注释还是很详细的

先上一段建表语句

drop database ormtest;create database ormtest;use ormtest;create table novel(    novelid char(36) PRIMARY  KEY ,    novelName varchar(20) UNIQUE,    currChap varchar(50),    rectChap varchar(50),    url varchar(100) NOT NULL,    encoding varchar(10) DEFAULT 'UTF-8');create table user(    userid char(36) PRIMARY KEY,    password varchar(20),    username varchar(20) UNIQUE,    nickname varchar(20) NOT NULL ,    email varchar(30) NOT NULL);

再来一个User类

package cn.omsfuk.domain;/** * Created by Administrator on 2017/4/8. */public class User {    private String userid;    private String username;    private String nickname;    private String password;    private String email;    public String getUserid() {        return userid;    }    public void setUserid(String userid) {        this.userid = userid;    }    public String getUsername() {        return username;    }    public void setUsername(String username) {        this.username = username;    }    public String getNickname() {        return nickname;    }    public void setNickname(String nickname) {        this.nickname = nickname;    }    public String getPassword() {        return password;    }    public void setPassword(String password) {        this.password = password;    }    public String getEmail() {        return email;    }    public void setEmail(String email) {        this.email = email;    }    @Override    public String toString() {        return userid + " " + username + " " + password + " " + nickname + " " + email;    }}

正主DBUtil类

package cn.omsfuk.simpleorm;import java.lang.reflect.Field;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.sql.*;import java.util.LinkedList;import java.util.List;/** * Created by omsfuk on 2017/4/8. */public class DBUtil {    private static Connection getConn() {        String url = "jdbc:mysql://localhost:3306/ormtest?useUnicode=true&characterEncoding=utf-8&useSSL=false&user=root&password=root";        Connection conn = null;        try {            Class.forName("com.mysql.jdbc.Driver");            conn = DriverManager.getConnection(url);        } catch (Exception e) {            e.printStackTrace();        }        return conn;    }    private static void close(AutoCloseable closeable) {        try {            if(closeable != null) {                closeable.close();            }        } catch (Exception e) {            e.printStackTrace();        }        closeable = null;    }    /**     * 查询。默认返回结果集合。需要用List接收。会自动根据这个对象里已有的信息自动补全sql语句。     * @param obj 要查询的对象。     * @return 结果List     */    public static List<Object> getObject(Object obj) {        Class cls = obj.getClass();        Method[] methods = cls.getMethods();        String sql = "select * from " + cls.getSimpleName() + " where ";        Field[] fields = cls.getDeclaredFields();        for(int i = 0; i < fields.length; i++) {            // 方法返回值类型            Class returnType = null;            // 返回值            Object returnValue = null;            try {                // 获得get方法                Method method = cls.getMethod("get" + (char)(fields[i].getName().charAt(0) - 32) + fields[i].getName().substring(1));                returnType = method.getReturnType();                // 调用方法，得到属性值                returnValue = method.invoke(obj);                // 补充sql语句                if(returnValue != null) {                    if(returnType == String.class) {                        sql += fields[i].getName() + "='" + returnType.cast(returnValue) + "' and ";                    } else {                        sql += fields[i].getName() + "=" + returnType.cast(returnValue) + " and ";                    }                }            } catch (NoSuchMethodException e) {                e.printStackTrace();            } catch (IllegalAccessException e) {                e.printStackTrace();            } catch (InvocationTargetException e) {                e.printStackTrace();            }        }        // 把最后一个and去掉        if(sql.endsWith("and ")) {            sql = sql.substring(0, sql.length() - 4);        }        // 处理查询        List<Object> result = new LinkedList<Object>();        Connection conn = null;        Statement stmt = null;        ResultSet rs = null;        try {            conn = getConn();            stmt = conn.createStatement();            rs = stmt.executeQuery(sql);            while(rs.next()) {                // 先创建一个实例对象，用来保存这一条记录                Object res = cls.newInstance();                for(int i = 0; i < fields.length; i++) {                    Field field = fields[i];                    try {                        // 获取set方法，用来给属性赋值                        Method method = cls.getMethod("set" + (char)(field.getName().charAt(0) - 32) + field.getName().substring(1),                                field.getType());                        // 调用方法，赋值                        if(fields[i].getType() == String.class) {                            method.invoke(res, rs.getString(field.getName()));                        } else {                            method.invoke(res, rs.getInt(field.getName()));                        }                    } catch (NoSuchMethodException e) {                        e.printStackTrace();                    } catch (InvocationTargetException e) {                        e.printStackTrace();                    }                }                // 将本条记录对应的对象添加到结果集中                result.add(res);            }        } catch (SQLException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        } catch (InstantiationException e) {            e.printStackTrace();        } finally {            close(rs);            close(stmt);            close(conn);        }        return result;    }    /**     * 插入新记录     * @param obj 要插入的对象，如果是uuid，请将setUserid之类的设置主键id的方法的内容设置为UUID()。如user.setUserid("UUID()");     * @return 是否插入成功     */    public static boolean insertObject(Object obj) {        Class cls = obj.getClass();        Method[] methods = cls.getMethods();        String sql = "insert " + cls.getSimpleName() + "(";        Field[] fields = cls.getDeclaredFields();        for (int i = 0; i < fields.length; i++) {            sql += fields[i].getName() + ", ";        }        sql = sql.substring(0, sql.length() - 2) + ") values(";        for (int i = 0; i < fields.length; i++) {            // 方法返回值类型            Class returnType = null;            // 返回值            Object returnValue = null;            try {                Method method = cls.getMethod("get" + (char)(fields[i].getName().charAt(0) - 32) + fields[i].getName().substring(1));                returnType = method.getReturnType();                returnValue = method.invoke(obj);                if(returnValue != null) {                    if(returnType.cast(returnValue).toString().toLowerCase().indexOf("uuid") != -1) {                        sql += returnType.cast(returnValue) + ", ";                    } else if(returnType == String.class) {                        sql += "'" + returnType.cast(returnValue) + "', ";                    } else {                        sql += returnType.cast(returnValue) + ", ";                    }                }            } catch (NoSuchMethodException e) {                e.printStackTrace();            } catch (IllegalAccessException e) {                e.printStackTrace();            } catch (InvocationTargetException e) {                e.printStackTrace();            }        }        sql = sql.substring(0, sql.length() - 2) + ")";        Connection conn = null;        Statement stmt = null;        boolean result = false;        try {            conn = getConn();            stmt = conn.createStatement();            if(stmt.executeUpdate(sql) == 1) {                result = true;            }        } catch (SQLException e) {            e.printStackTrace();        } finally {            close(stmt);            close(conn);        }        return result;    }}

再来一个测试类

package cn.omsfuk;import cn.omsfuk.domain.User;import cn.omsfuk.simpleorm.DBUtil;import org.junit.Test;import java.util.List;/** * Created by Administrator on 2017/4/8. */public class DBUtilTest {    @Test    public void insertObject() {        User user = new User();        user.setUserid("UUID()");        user.setPassword("admin");        user.setUsername("omsfuk");        user.setEmail("[e-mail]");        user.setNickname("逗逼");        DBUtil.insertObject(user);    }    @Test    public void getObject() {        User user = new User();        user.setUsername("omsfuk");        List<Object> result = DBUtil.getObject(user);        for(Object obj : result) {            User usr = (User) obj;            System.out.println(usr);        }    }}

运行测试，输出

2152589c-1c73-11e7-8ca6-afc3c17f389b omsfuk admin 逗逼 [e-mail]

OK，成功。