Is there a way to take an argument in a callable method?

问题

I have created a piece of code which takes an IP address (from main method in another class) and then loops through a range of IP addresses pinging each one as it goes. I have a GUI front end on this and it was crashing (hence why I've done the multithreading. My problem is I can no longer take the IP address as an argument in my ping code as its callable. I've searched all over for this and cant seem to find a way to get round this. Is there a way for a callable method to take arguments? If not is there any other way to accomplish what I'm trying to do?

sample of my code:

public class doPing implements Callable<String>{

public String call() throws Exception{

    String pingOutput = null;

    //gets IP address and places into new IP object
    InetAddress IPAddress = InetAddress.getByName(IPtoPing);
    //finds if IP is reachable or not. a timeout timer of 3000 milliseconds is set.
    //Results can vary depending on permissions so cmd method of doing this has also been added as backup
    boolean reachable = IPAddress.isReachable(1400);

    if (reachable){
          pingOutput = IPtoPing + " is reachable.\n";
    }else{
        //runs ping command once on the IP address in CMD
        Process ping = Runtime.getRuntime().exec("ping " + IPtoPing + " -n 1 -w 300");
        //reads input from command line
        BufferedReader in = new BufferedReader(new InputStreamReader(ping.getInputStream()));
        String line;
        int lineCount = 0;
        while ((line = in.readLine()) != null) {
            //increase line count to find part of command prompt output that we want
            lineCount++;
            //when line count is 3 print result
            if (lineCount == 3){
                pingOutput = "Ping to " + IPtoPing + ": " + line + "\n";
            }
        }
    }
    return pingOutput;
}
}

IPtoPing used to be the argument that was taken.

回答1:

You can't pass it as the argument to call() because the method signature doesn't allow it.

However, you can pass it as a constructor argument; e.g.

public class DoPing implements Callable<String>{
    private final String ipToPing;

    public DoPing(String ipToPing) {
        this.ipToPing = ipToPing;
    }

    public String call() throws SomeException {
        InetAddress ipAddress = InetAddress.getByName(ipToPing);
        ....
    }
}

(I've corrected a couple of egregious code style violations!!)

Alternatively, you could:

declare DoPing as an inner class and have it refer to a final ipToPing in the enclosing scope, or
add a setIpToPing(String ipToPing) method.

(The last allows a DoPing object to be reused, but the downside is that you will need to synchronize to access it thread-safely.)

回答2:

Adding to Jarle's answer -- in case you create Callable as instance of anonymous class, you can use final field outside of anonymous class for passing data into the instance:

    final int arg = 64;
    executor.submit(new Callable<Integer>() {
        public Integer call() throws Exception {
            return arg * 2;
        }
    });

回答3:

When you create the doPing-class (should be captial letter in class name), send in the ip-address in the constructor. Use this ip-address in the call-method.

回答4:

You can't pass arguments to call() because the method signature doesn't allow it but here is at least one way to work around that by

defining an abstract class that wraps/implements Callable and
implementing a setter to "inject" a result into call()

Define an abstract class:

import java.util.concurrent.Callable;

public abstract class Callback<T> implements Callable<Void> {
    T result;

    void setResult (T result) {
        this.result = result;
    }

    public abstract Void call ();
}

Define the method that should fire the callback:

public void iWillFireTheCallback (Callback callback) {
    // You could also specify the signature like so:
    // Callback<Type of result> callback

    // make some information ("the result")
    // available to the callback function:
    callback.setResult("Some result");

    // fire the callback:
    callback.call();
}

In the place where you want to call iWillFireTheCallback:

Define the callback function (even possible inside methods):

class MyCallback extends Callback {
    @Override
    public Void call () {
        // this is the actual callback function

        // the result variable is available right away:
        Log.d("Callback", "The result is: " + result);

        return null;
    }
}

And then call iWillFireTheCallback while passing in the callback:

iWillFireTheCallback(new MyCallback());

回答5:

Put some (final) fields in your doPing class, and a constructor that initializes them, then pass the values you want to use in call() to the constructor of doPing:

public class doPing implements Callable<String>  {
     private final String ipToPing;

     public doPing(String ip) {
         this.ipToPing = ip;
     }

     public String call() {
         // use ipToPing
     }
}

回答6:

You have to defien a property such as ipAddress and its accessor method. and passing its value in constructor or by setter method. In doPing class use ipAddress property.

class DoPing/* In java all classes start with capital letter */implements Callable<String>
{
    private String  ipAddress;

    public String getIpAddress()
    {
        return ipAddress;
    }

    public void setIpAddress(String ipAddress)
    {
        this.ipAddress = ipAddress;
    }

    /*
     * Counstructor 
     */
    public DoPing(String ipAddress )
    {
        this.ipAddress = ipAddress;
    }

    @Override
    public String call() throws Exception
    {
        // your logic
    }
}

来源：https://stackoverflow.com/questions/9992992/is-there-a-way-to-take-an-argument-in-a-callable-method

标签

java

multithreading

arguments

ping

callable