ThreadLocal（jdk中）

线程容器,给线程绑定一个 Object 内容,后只要线程不变,可以随时取出.改变线程,无法取出内容.

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final ThreadLocal<String> threadLocal = new ThreadLocal<>();
threadLocal.set("测试"); new Thread(){ 
    public void run() { 
        String result = threadLocal.get(); 
        System.out.println("结果:"+result); 
        }; 
    }.start();

利用这一特性优化mybatis中service加载配置文件，创建session代码

MyUtil

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package com.kylin.util;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;

public class MyBatisUtil {
    //factory实例化的过程是一个比较耗费性能的过程
    //保证有且只有一个factory
    private static SqlSessionFactory factory;
    private static ThreadLocal<SqlSession> tl = new ThreadLocal<>();
    static {
        try {
            InputStream is = Resources.getResourceAsStream("mybatis.xml");
            factory = new SqlSessionFactoryBuilder().build(is);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * 获取SqlSession的方法
     * @return
     */
    public static SqlSession getSession(){
        SqlSession session = tl.get();
        if (session==null){
            tl.set(factory.openSession());
        }
        return tl.get();
    }

    public  static  void closeSession(){
        SqlSession session = tl.get();
        if (session!=null){
            session.close();
        }
        tl.set(null);
    }
}

OpenSessionInView

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package com.kylin.filter;

import com.kylin.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;


import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;

/**
 * 最开始是有Spring框架提出的，整合Hibernate框架是使用的是OpenSessionInView
 */
@WebFilter("/*")
public class OpenSessionInView implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        /*InputStream is = Resources.getResourceAsStream("mybatis.xml");
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
        SqlSession session = factory.openSession();*/
        SqlSession session = MyBatisUtil.getSession();
        try {
            filterChain.doFilter(servletRequest,servletResponse);
            session.commit();
        }catch (Exception e){
            session.rollback();
            e.printStackTrace();
        }finally {
            MyBatisUtil.closeSession();
        }
    }

    @Override
    public void destroy() {

    }
}

InsertServlet

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package com.kylin.Servlet;

import com.kylin.pojo.Log;
import com.kylin.service.LogService;
import com.kylin.service.impl.LogServiceImpl;

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

@WebServlet("/insert")
public class InsertServlet extends HttpServlet {
    private  LogService logService = new LogServiceImpl();
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        Log log = new Log();
        log.setAccIn(req.getParameter("accin"));
        log.setAccOut(req.getParameter("accout"));
        log.setMoney(Double.parseDouble(req.getParameter("money")));
        int index = logService.ins(log);
        if (index>0){
            resp.sendRedirect("success.jsp");
        }else {
            resp.sendRedirect("/os/error.jsp");
        }
    }
}

LogServiceImpl

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package com.kylin.service.impl;

import com.kylin.mapper.LogMapper;
import com.kylin.pojo.Log;
import com.kylin.service.LogService;
import com.kylin.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;

public class LogServiceImpl implements LogService {
    @Override
    public int ins(Log log) {
        SqlSession session = MyBatisUtil.getSession();
        LogMapper mapper = session.getMapper(LogMapper.class);
        return mapper.ins(log);
    }
}

具体过程和代码意义：