Why two conditions has different result: @Autowired

Question

Today, I met a problem about the annotation of spring. The annotation is @Autowired. where in the Code, the @Autowired is play a role in the CommandController class, but I found the injection of autowired in readVoltageThread class don't work, and occured error of NullPointerException when run the readVoltagemethod.

@Controller
@RequestMapping("/dongjun")
@SessionAttributes("currentUser")
public class CommandController {

    @Autowired
    private SimpMessagingTemplate template;

    @Autowired
    public CommandController(SimpMessagingTemplate template) {
        this.template = template;
    }

    @RequestMapping("/read_voltage")
    @ResponseBody
    public void readVoltage(@RequestParam(required = true) String switchId,
            String type) {

        ReadVoltageThread readVoltageThread = new ReadVoltageThread(type, switchId, template);
        readVoltageThread.setDaemon(true);
        readVoltageThread.start();
    }
}

class ReadVoltageThread extends Thread {


    @Autowired
    private HighVoltageCurrentService currentService2;
    @Autowired
    private HighVoltageVoltageService voltageService2;

    @Autowired
    public HighVoltageHitchEventService eventService;

    private String type;
    private String switchId;
    private SimpMessagingTemplate template;

    public ReadVoltageThread(String type, String switchId, SimpMessagingTemplate template) {
        this.type = type;
        this.switchId = switchId;
        this.template = template;
    }


    @Override
    public void run() {

        while(true) {
            try {
                sleep(5000);
                template.convertAndSend("/topic/read_voltage", 
                    readVoltage(type, switchId));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    private Object readVoltage(String type, String switchId) {
        Integer[] deStrings = new Integer[3];
        switch (type) {
        case "0":break;

        case "1"://highVoltage

            List<HighVoltageVoltage> cliList2 = voltageService2
                    .getRecentlyVoltage(switchId, "A");
            if (cliList2 != null && cliList2.size() != 0) {
                 deStrings[0] = cliList2.get(0).getValue();
            }

            cliList2 = voltageService2
                    .getRecentlyVoltage(switchId, "B");
            if (cliList2 != null && cliList2.size() != 0) {
                deStrings[1] = cliList2.get(0).getValue();
            }
            cliList2 = voltageService2
                    .getRecentlyVoltage(switchId, "C");
            if (cliList2 != null && cliList2.size() != 0) {
                deStrings[2] = cliList2.get(0).getValue();
            }
            break;
        case "2":break;

        default:
            break;
        }
        return deStrings;
    }
}

How I fix it.Thanks.

score 2 · Accepted Answer · answered May 04 '16 at 10:42

When you create the ReadVoltageThread using new, Spring has no knowledge about it, meaning @Autowired and all other annotations won't work.

You need to autowire the ReadVoltageThread too so it's managed by Spring, although I suspect that your design has other issues making a proper fix involve a lot more than that.

Why two conditions has different result: @Autowired

1 Answers1