简单的反射实现JDBC操作

落日映苍穹つ 2021-11-11 09:00 225阅读 0赞

**1. 创建User.java文件**

/**
     1. @Author: Chendc
     2. @Date: 2019/7/23 19:57
     */
    public class User {
        private Long id;
        private String name;
        private Long age;
        private String email;
    
        public Long getId() {
            return id;
        }
    
        public void setId(Long id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Long getAge() {
            return age;
        }
    
        public void setAge(Long age) {
            this.age = age;
        }
    
        public String getEmail() {
            return email;
        }
    
        public void setEmail(String email) {
            this.email = email;
        }
    
        @Override
        public String toString() {
            return "User{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", age=" + age +
                    ", email='" + email + '\'' +
                    '}';
        }

**2.MySQL中创建对应的表结构**

DROP TABLE IF EXISTS `user`;
    CREATE TABLE `user` (
      `id` int(6) NOT NULL,
      `name` varchar(255) DEFAULT NULL,
      `age` int(6) DEFAULT NULL,
      `email` varchar(255) DEFAULT NULL,
      PRIMARY KEY (`id`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

**3.开始撸反射代码**

/**
     * @Author: Chendc
     * @Date: 2019/8/5 8:51
     */
    public class SQLUtil {
        /**
         * JDBC连接数据库
         * @return
         */
        public static Connection getJDBCConnection(){
            Connection conn = null;
            try {
                String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=GMT%2B8";
                String username="root";
                String password="yourself password";
                conn = DriverManager.getConnection(url, username, password);
            }catch (SQLException e) {
                e.printStackTrace();
            }
            return conn;
        }
    
        /**
         * 反射对象 组装Insert SQL语句
         * @param object
         * @return Insert SQL语句
         */
        public static void CreateInsertSQL(Object object){
            StringBuffer sql = new StringBuffer("INSERT INTO ");
            Class c = object.getClass();
            //获取对象所有方法
            Method[] methods = c.getMethods();
            //获取对象所有属性
            /*Field[] fields = c.getFields();*/
            //获取对象的类名称
            String className = c.getName();
            //根据类名 获取SQL表名
            String tableName = className.substring(className.lastIndexOf(".") + 1,className.length());
            sql.append(tableName + "(");
            //获取对象所有的属性名称
            List<String> kList = new ArrayList<String>();
            //获取所有get方法的返回值
            List vList = new ArrayList();
            //遍历get方法 截取"get"字符串 获取属性名称
            for (Method method : methods){
                String methodName = method.getName();
                if (methodName.startsWith("get") && !methodName.startsWith("getClass")){
                    String fieldName = methodName.substring(3,methodName.length());
                    kList.add(fieldName);
                    //根据实现Get方法 获取对象的属性值
                    try {
                        Object value = method.invoke(object, null);
                        //将String类型值转换为数据库字符串值（String ==> "String"）
                        if (value instanceof String){
                            vList.add("\""+ value + "\"");
                        }else{
                            vList.add(value);
                        }
                    } catch (IllegalAccessException e) {
                        e.printStackTrace();
                    } catch (InvocationTargetException e) {
                        e.printStackTrace();
                    }
                }
            }
            //将得到的属性名称集合进行SQL字段语句拼接
            for (int i=0; i<kList.size(); i++){
                if (i<kList.size()-1){
                    sql.append(kList.get(i)+",");
                }else{
                    sql.append(kList.get(i)+")\tvalue(");
                }
            }
            //将得到的属性值集合进行SQL字段值语句拼接
            for (int i=0; i<vList.size(); i++){
                if (i<kList.size()-1){
                    sql.append(vList.get(i)+",");
                }else{
                    sql.append(vList.get(i)+");");
                }
            }
            try {
                PreparedStatement p = getJDBCConnection().prepareStatement(sql.toString());
                p.execute();
                System.out.println("EXECUTE_RESULT：SUCCESS\n"+"SQL_MESSAGE："+sql.toString());
            } catch (SQLException e) {
                System.out.println("EXECUTE_RESULT：ERROR\n"+"ERROR_MESSAGE："+e.getMessage());
            }
        }
    
        /**
         * SQL查询数据 转换对象
         * @param className ("com.demo.domain.XXX")
         * @param id (Entity.getId())
         * @return Entity
         */
        public static Object selectById(String className,Long id){
            Object o = null;
            try {
                Class cEntity = Class.forName(className);
                //通过字节码名得到表面
                String tableName = className.substring(className.lastIndexOf(".")+1, className.length());
                //拼接SQL查询语句
                StringBuffer sql = new StringBuffer();
                sql.append("SELECT * FROM " + tableName + " WHERE ID =" + id);
                System.out.println("SEARCH_SQL：" + sql);
                try {
                    //执行SQL语句得到结果集
                    PreparedStatement pre = getJDBCConnection().prepareStatement(sql.toString());
                    ResultSet resultSet = pre.executeQuery();
                    while(resultSet.next()){
                        //通过Class.ForName反射得到实例对象
                        o = cEntity.newInstance();
                        //得到所有的set方法
                        Method[] methods = cEntity.getMethods();
                        for (Method method : methods){
                            String methodName = method.getName();
                            //过滤出set属性方法进行对象赋值
                            if (methodName.startsWith("set")){
                                //通过方法名获取字段名
                                String columnName = methodName.substring(3,methodName.length());
                                //得到方法参数类型
                                Class[] parameterTypes = method.getParameterTypes();
                                if (parameterTypes[0] == String.class){
                                    method.invoke(o,resultSet.getString(columnName));
                                }
                                if (parameterTypes[0] == Long.class){
                                    method.invoke(o,resultSet.getLong(columnName));
                                }
                            }
                        }
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                } catch (InstantiationException e) {
                    e.printStackTrace();
                } catch (InvocationTargetException e) {
                    e.printStackTrace();
                }
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
            return o;
        }
    	//测试编写的方法
     	public static void main(String[] args) {
            //执行Insert方法
            User user1 = new User();
            user1.setId(3L);
            user1.setName("张三");
            user1.setAge(25L);
            user1.setEmail("16300@163email.com");
            CreateInsertSQL(user1);
            //执行Select方法
            //com.demo.domain.User 改成自己 User所在的路径
            User user2 = (User) selectById("com.demo.domain.User", 3L);
            System.out.println(user2.toString());
        }
    }