spring boot 使用ThreadLocal例項
阿新 • • 發佈:2018-11-09
本文參考慕課教程給出一個在spring boot中使用ThreadLocal實現執行緒封閉的例項。
首先建立一個包含ThreadLocal成員變數的例項:
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(); } }
編寫一個Controller類,請求該類的test()方法獲取ThreadLocal中儲存的id:
import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.ResponseBody; @Controller @RequestMapping("/threadLocal") public class ThreadLocalController { @RequestMapping("/test") @ResponseBody public Long test() { return RequestHolder.getId(); } }
編寫過濾器,在請求到達Servlet之前(請求->tomcat容器->filter->servlet->inteceptor->controller),將當前執行緒的id新增到ThreadLocal中:
import com.mmall.concurrency.example.threadLocal.RequestHolder; import lombok.extern.slf4j.Slf4j; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletRequest; import java.io.IOException; @Slf4j 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; log.info("do filter, {}, {}", Thread.currentThread().getId(), request.getServletPath()); //在ThreadLocal中添加當前執行緒的id RequestHolder.add(Thread.currentThread().getId()); filterChain.doFilter(servletRequest, servletResponse); } @Override public void destroy() { } }
編寫攔截器,當請求處理完成後(從Controller返回後),清除ThreadLocal中的id,避免記憶體洩漏。
import com.mmall.concurrency.example.threadLocal.RequestHolder;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@Slf4j
public class HttpInterceptor extends HandlerInterceptorAdapter {
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
log.info("preHandle");
return true;
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
log.info("ThreadId:"+RequestHolder.getId());
RequestHolder.remove();
log.info("afterCompletion");
return;
}
}
最後,我們需要在spring boot啟動類上註冊我們定義的Filer及Inteceptor,並設定攔截路徑。
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.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
@SpringBootApplication
public class ConcurrencyApplication extends WebMvcConfigurerAdapter{
public static void main(String[] args) {
SpringApplication.run(ConcurrencyApplication.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("/**");
}
}
在瀏覽器或者postman中輸入http://localhost:8080/threadLocal/test
觀察輸出結果:
2018-11-09 11:16:51.287 INFO 34076 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
2018-11-09 11:16:51.290 INFO 34076 --- [ main] c.m.concurrency.ConcurrencyApplication : Started ConcurrencyApplication in 1.718 seconds (JVM running for 2.132)
2018-11-09 11:17:03.060 INFO 34076 --- [nio-8080-exec-2] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring FrameworkServlet 'dispatcherServlet'
2018-11-09 11:17:03.060 INFO 34076 --- [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet : FrameworkServlet 'dispatcherServlet': initialization started
2018-11-09 11:17:03.072 INFO 34076 --- [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet : FrameworkServlet 'dispatcherServlet': initialization completed in 12 ms
2018-11-09 11:17:03.078 INFO 34076 --- [nio-8080-exec-2] com.mmall.concurrency.HttpFilter : do filter, 29, /threadLocal/test
2018-11-09 11:17:03.090 INFO 34076 --- [nio-8080-exec-2] com.mmall.concurrency.HttpInterceptor : preHandle
2018-11-09 11:17:03.124 INFO 34076 --- [nio-8080-exec-2] com.mmall.concurrency.HttpInterceptor : ThreadId:29
2018-11-09 11:17:03.124 INFO 34076 --- [nio-8080-exec-2] com.mmall.concurrency.HttpInterceptor : afterCompletion
從列印的日誌結果中,我們看到在Filter中我們將當前執行緒的id 29新增到了ThreadLocal中,隨後在Inteceptor中列印並刪除了id。