6.4线程封闭

线程封闭

线程封闭：把对象封装到一个线程里，只有这一个线程能看到这个对象，这样，即使该对象不是线程安全的，也不会带来线程安全问题

如何实现线程封闭？

• Ad-hoc线程封闭：程序控制实现，最糟糕，忽略

• 堆栈封闭：局部变量，无并发问题。多个线程访问一个方法的时候，每个线程都会拷贝一份局部变量到线程的栈中。

• ThreadLocal线程封闭：特别好的封闭方法，ThreadLocal内部是一个map，map的key是线程的名称，map的值就是我们要封闭的对象

演示ThreadLocal

1.创建一个bean

package com.moluo.moapi.security.filter;

public class RequestHolder {

    private final static ThreadLocal<Long> requestHolder = new ThreadLocal<>();

    public static void add(Long id) {
        requestHolder.set(id);
    }

    public static Long getId() {
        return requestHolder.get();
    }

    public static void remove() {
        requestHolder.remove();
    }

}

1. 使用过滤器向ThreadLocal中放数据

package com.moluo.moapi.security.filter;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

public class HttpFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        System.out.println("do filter," + Thread.currentThread().getId() + ", " + request.getServletPath());
        RequestHolder.add(Thread.currentThread().getId());
        filterChain.doFilter(servletRequest, servletResponse);
    }

    @Override
    public void destroy() {

    }
}

注册过滤器

package com.moluo.moapi;

import com.moluo.moapi.security.filter.HttpFilter;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.data.jpa.repository.config.EnableJpaAuditing;

@SpringBootApplication
@EnableJpaAuditing
public class MoApiApplication {

    public static void main(String[] args) {
        SpringApplication.run(MoApiApplication.class, args);
    }

    @Bean
    public FilterRegistrationBean httpFilter() {
        FilterRegistrationBean registrationBean = new FilterRegistrationBean();
        registrationBean.setFilter(new HttpFilter());
        registrationBean.addUrlPatterns("/threadLocal/*");
        return registrationBean;
    }
}

3.使用拦截器在方法处理完后移除ThreadLocal中的数据

package com.moluo.moapi.security.filter;

import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HttpInterceptor extends HandlerInterceptorAdapter {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("preHandle");
        return true;
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        RequestHolder.remove();
        System.out.println("afterCompletion");
    }
}

注册拦截器(继承WebMvcConfigurerAdapter类，重写addInterceptors方法)

package com.moluo.moapi;

import com.moluo.moapi.security.filter.HttpFilter;
import com.moluo.moapi.security.filter.HttpInterceptor;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.data.jpa.repository.config.EnableJpaAuditing;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@SpringBootApplication
@EnableJpaAuditing
public class MoApiApplication extends WebMvcConfigurerAdapter {

    public static void main(String[] args) {
        SpringApplication.run(MoApiApplication.class, args);
    }

    @Bean
    public FilterRegistrationBean httpFilter() {
        FilterRegistrationBean registrationBean = new FilterRegistrationBean();
        registrationBean.setFilter(new HttpFilter());
        registrationBean.addUrlPatterns("/threadLocal/*");
        return registrationBean;
    }

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new HttpInterceptor()).addPathPatterns("/**");
    }
}

4.controller

package com.moluo.moapi.security.controller;

import com.moluo.moapi.security.filter.RequestHolder;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/threadLocal")
public class ThreadLocalController {

    @GetMapping("/test")
    public Long test() {
        return RequestHolder.getId();
    }
}

5.使用postman访问 GET http://127.0.0.1:8080/threadLocal/test 将返回线程ID