okhttp-gson: allow array parameters in path using collectionFormat (#2137)

* okhttp-gson: allow array parameters in path using collectionFormat

* run bin/java-petstore-okhttp-gson-parcelable.sh

samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/ApiClient.java

@@ -637,6 +637,40 @@ public class ApiClient {
         return params;
     }
 
+    /**
+     * Formats the specified collection path parameter to a string value.
+     *
+     * @param collectionFormat The collection format of the parameter.
+     * @param value The value of the parameter.
+     * @return String representation of the parameter
+     */
+    public String collectionPathParameterToString(String collectionFormat, Collection value) {
+        // create the value based on the collection format
+        if ("multi".equals(collectionFormat)) {
+            // not valid for path params
+            return parameterToString(value);
+        }
+
+        // collectionFormat is assumed to be "csv" by default
+        String delimiter = ",";
+
+        if ("ssv".equals(collectionFormat)) {
+            delimiter = " ";
+        } else if ("tsv".equals(collectionFormat)) {
+            delimiter = "\t";
+        } else if ("pipes".equals(collectionFormat)) {
+            delimiter = "|";
+        }
+
+        StringBuilder sb = new StringBuilder() ;
+        for (Object item : value) {
+            sb.append(delimiter);
+            sb.append(parameterToString(item));
+        }
+
+        return sb.substring(delimiter.length());
+    }
+
     /**
      * Sanitize filename by removing path.
      * e.g. ../../sun.gif becomes sun.gif