Tracing calls

Earlier, we saw a screenshot from Chrome's debug tools, showing request and response headers. There is another tool we can use as well--Spring Boot Actuator's trace endpoint.

By visiting http://localhost:8080/application/trace, we can see all the web calls, going back in time. For example, look at this request to negotiate the WebSocket:

    { 
      "timestamp": 1480805242289, 
      "info": { 
        "method": "GET", 
        "path": "/learning-spring-boot/160/ge00bkmu/websocket", 
        "headers": { 
          "request": { 
            "host": "localhost:8080", 
            "connection": "Upgrade", 
            "pragma": "no-cache", 
            "cache-control": "no-cache", 
            "authorization": "Basic Z3JlZzp0dXJucXVpc3Q=", 
            "upgrade": "websocket", 
            "origin": "http://localhost:8080", 
            "sec-websocket-version": "13", 
            "user-agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 
              10_11_5) AppleWebKit/537.36 (KHTML...