Best practice for passing many arguments to method?

In Effective Java, Chapter 7 (Methods), Item 40 (Design method signatures carefully), Bloch writes:

There are three techniques for shortening overly long parameter lists:

break the method into multiple methods, each which require only a subset of the parameters
create helper classes to hold group of parameters (typically static member classes)
adapt the Builder pattern from object construction to method invocation.

For more details, I encourage you to buy the book, it's really worth it.

Using a map with magical String keys is a bad idea. You lose any compile time checking, and it's really unclear what the required parameters are. You'd need to write very complete documentation to make up for it. Will you remember in a few weeks what those Strings are without looking at the code? What if you made a typo? Use the wrong type? You won't find out until you run the code.

Instead use a model. Make a class which will be a container for all those parameters. That way you keep the type safety of Java. You can also pass that object around to other methods, put it in collections, etc.

Of course if the set of parameters isn't used elsewhere or passed around, a dedicated model may be overkill. There's a balance to be struck, so use common sense.

If you have many optional parameters you can create fluent API: replace single method with the chain of methods

exportWithParams().datesBetween(date1,date2)
                  .format("xml")
                  .columns("id","name","phone")
                  .table("angry_robots")
                  .invoke();

Using static import you can create inner fluent APIs:

... .datesBetween(from(date1).to(date2)) ...

It's called "Introduce Parameter Object". If you find yourself passing same parameter list on several places, just create a class which holds them all.

XXXParameter param = new XXXParameter(objA, objB, date1, date2, str1, str2);
// ...
doSomething(param);

Even if you don't find yourself passing same parameter list so often, that easy refactoring will still improve your code readability, which is always good. If you look at your code 3 months later, it will be easier to comprehend when you need to fix a bug or add a feature.

It's a general philosophy of course, and since you haven't provided any details, I cannot give you more detailed advice either. :-)

First, I'd try to refactor the method. If it's using that many parameters it may be too long any way. Breaking it down would both improve the code and potentially reduce the number of parameters to each method. You might also be able to refactor the entire operation to its own class. Second, I'd look for other instances where I'm using the same (or superset) of the same parameter list. If you have multiple instances, then it likely signals that these properties belong together. In that case, create a class to hold the parameters and use it. Lastly, I'd evaluate whether the number of parameters makes it worth creating a map object to improve code readability. I think this is a personal call -- there is pain each way with this solution and where the trade-off point is may differ. For six parameters I probably wouldn't do it. For 10 I probably would (if none of the other methods worked first).

Best practice for passing many arguments to method?

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