How do I consume c# WebMethod that returns List> through my java client?

Question

I have an asmx webservice in C# where the webmethod GetKeys() returns a List<List<string>> however when I consume the webmethod in my java client through my proxy GetKeys() is of the type Object[]. Because of this I cannot figure out a way to access the strings. Ideally I would like to parse the C# List<List<string>> to an ArrayList<String[]> but I am open to easier solutions. I need to display the contents in a JTable.

Any help with this or tips on how I could solve this another way would be much appreciated.

Here are the relevant methods:

    public class ProgAss5WebService : System.Web.Services.WebService
        {
            [WebMethod]
            public List<List<string>> GetKeys()
            {
                return dal.GetKeysList();
            }
} //End of C# WebService class

public class Controller { //Java client
public void getKeys() {
        ArrayList<String[]> rowList = new ArrayList<String[]>();
        try {
            //This works
            Object[] myArr = proxy.getKeys();
            
            //This does not
            rowList = proxy.getKeys();
            
        }catch(RemoteException e) {
            e.printStackTrace();
        }
    }
}//End of Controller class

I am still learning the proper way of SO so please tell me if more information is needed and correct any mistakes in my question. Thank you!

This will most likely deserialize to an array of an array of strings. Debug, inspect and cast accordingly. I am no Java guy but I imagine this must be easy to handle once you look at the underlying type. — JuanR, Mar 31 '22 at 22:59

score 0 · Answer 1 · answered Mar 31 '22 at 20:33

Your C# method is being deserialized and reserialized in the background. Java does not know what a List<List<String>> is, so it makes it into a list of objects. You then cast that list of objects. There are probably faster/better ways to do this, but I'm not a Java expert and this should be good enough:

for (i = 0; i < myArr.length; i++) {
   var x = ar[i];
   rowList.Add((List<String>)x;
}

score 0 · Answer 2 · answered Apr 02 '22 at 20:12

I found a way to solve my problem. I changed the List<List> into a C# jagged array which seems to be basically the same as a multidimensional array in Java. I tried the solution with a C# multidimensional array but I got an error messaage that said multidimensional arrays where not supported(unfortunately I don't have a copy of the error msg). By properly reading the Documentaion I figured out how to use the jagged array which made the code very simple.

public class ProgAss5WebService : System.Web.Services.WebService
        {
            [WebMethod]
            public string[][] GetKeys()
            {
                return dal.GetKeysList();
            }
} //End of C# WebService class

public class Controller { //Java client
public void getKeys() {
        ArrayList<String[]> rowList = new ArrayList<String[]>();
        try {
//This works
String[][] = proxy.GetKeys(); //Before, the proxy method would be of the wrong type

        //Then I parse the 2D string array to an ArrayList<String[]>    
        for (int rowIndex = 0; rowIndex < stringArr[0].length; rowIndex++) { // loops through the rows of the 2d stringArr

            String[] row = new String[stringArr.length];// For each row it creates a new string array containing the values

            for (int columnIndex = 0; columnIndex < stringArr.length; columnIndex++) { // loops through the cells of each row
                row[columnIndex] = stringArr[columnIndex][rowIndex].toString(); // casts the values of 2d stringArr
            }
            rowList.add(row); // adds the String[] to the arrayList
        }

        return rowList;
    }
}//End of Controller class

How do I consume c# WebMethod that returns List> through my java client?

2 Answers2