前端项目总结redis,jedis,BaseServlet,反射

redis

redis特点:

1. redis命令是nosql的，什么是nosql：
   不按照标准规定的sql语句来操作数据库
2. redis能把数据存在内存中（eg：将数据库中的数据存在内存中，防止再次查询数据时消耗大量的资源和时间）

							  数据库中的信息
								uid  uname
								 1	  呵呵
								 2    小黄
								 3    小明
《--------------------------------------------------------------------》
//1.从redis中查询
        //1.1获取jedis客户端
        Jedis jedis = JedisUtil.getJedis();
        //1.2可使用sortedset排序查询
        Set<String> categorys = jedis.zrange("category", 0, -1);
        System.out.println(categorys);
        //2.判断查询的集合是否为空
        List<Category> list = null;
        if (categorys==null || categorys.size()==0){
            //3.如果为空,从数据库查询,再将数据库存入redis
            //3.1从数据库查询
            list = categoryDao.findAll();
            //3.2将集合数据存到redis中的 catefory的key
            for (int i = 0; i < list.size(); i++) {

                jedis.zadd("category",list.get(i).getCid(),list.get(i).getCname());

            }

jedis

操作redis的一个jar包
下面的连接工具其实是为了有更好的代码体验

其实可以只需要创建
public Jedis() {
 }

 public Jedis(String host) {
     super(host);
 }

 public Jedis(String host, int port) {
     super(host, port);
 }

 public Jedis(String host, int port, int timeout) {
     super(host, port, timeout);
 }

 public Jedis(String host, int port, int connectionTimeout, int soTimeout) {
     super(host, port, connectionTimeout, soTimeout);
 }

package cn.itcast.travel.util;

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

/**
 * Jedis工具类
 */
public final class JedisUtil {
    private static JedisPool jedisPool;

    static {
        //读取配置文件
        InputStream is = JedisPool.class.getClassLoader().getResourceAsStream("jedis.properties");
        //创建Properties对象
        Properties pro = new Properties();
        //关联文件
        try {
            pro.load(is);
        } catch (IOException e) {
            e.printStackTrace();
        }
        //获取数据，设置到JedisPoolConfig中
        JedisPoolConfig config = new JedisPoolConfig();
        config.setMaxTotal(Integer.parseInt(pro.getProperty("maxTotal")));
        config.setMaxIdle(Integer.parseInt(pro.getProperty("maxIdle")));

        //初始化JedisPool
        jedisPool = new JedisPool(config, pro.getProperty("host"), Integer.parseInt(pro.getProperty("port")));


    }


    /**
     * 获取连接方法
     */
    public static Jedis getJedis() {
        return jedisPool.getResource();
    }

    /**
     * 关闭Jedis
     */
    public static void close(Jedis jedis) {
        if (jedis != null) {
            jedis.close();
        }
    }
}

BaseServlet

由于Servlet写多了之后会出现代码冗余等问题，所以就可以直接通过一个路径名来调用方法，达到简化代码的效果
BaseServlet的实现其实是：反射
当CategoryServlet类 extends BaseServlet输入的方法名会加入在路径后面，反射就可以获取这个名字，通过这个名字来调用CategoryServlet类方法

其次反射中如果用暴力反射，就要加上

method.setAccessible(true);

什么是暴力反射呢？
getDeclaredMethod（String name,...obj.class（可以为空））：获取该名类的所有方法

Method method = this.getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);

package cn.itcast.travel.web.servlet;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class BaseServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.获取请求路径
        String uri = req.getRequestURI();
//        System.out.println("UserServlet路径："+uri);//  /travel/user/add
        //2.获取方法名
        String methodName = uri.substring(uri.lastIndexOf('/') + 1);//add
//        System.out.println(methodName);
        //3.获取方法对象Method
        //谁调用我,this就是谁
//        System.out.println(this);
        try {
            //忽略权限修饰符，获取方法对象
            Method method = this.getClass().getMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            //暴力反射
            //4.执行方法
            method.invoke(this,req,resp);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
    }
}

package cn.itcast.travel.web.servlet;

import cn.itcast.travel.domain.Category;
import cn.itcast.travel.service.CategoryService;
import cn.itcast.travel.service.impl.CategoryServiceImpl;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

@WebServlet("/category/*")
//继承于BaseServlet 
<------------------------------------------------------------------>
//当访问这个路径时候就会给与findAll方法名
<------------------------------------------------------------------>
//例如/category/findAll
public class CategoryServlet extends BaseServlet {

    private CategoryService service = new CategoryServiceImpl();

    /**
     * 查询所有
     * @param request
     * @param response
     * @throws ServletException
     * @throws IOException
     */
    public void findAll(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.调用service查询所有
        List<Category> cs = service.findAll();
        //2.序列化json返回
       /* ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString("cs");*/
       writerValue(cs,response);


    }
}

req.getRequestURI与req.getContextType区别

//1.获取请求的URI路径
        String uri = req.getRequestURI();
        输出：/travel/user/add
//2.获取请求的虚拟路径
		String contentPath = req.getContextType();
		输出：/travel