Add parameterToString to normalize parameters for Java client

* Convert values to string for query/header/form parameters.
* For parameter of type Date, convert to ISO 8601 format.
* Also add utility methods to parse date in ISO 8601 format.

modules/swagger-codegen/src/main/resources/Java/api.mustache

@@ -59,9 +59,9 @@ public class {{classname}} {
     Map<String, String> formParams = new HashMap<String, String>();
 
     {{#queryParams}}if ({{paramName}} != null)
-      queryParams.put("{{baseName}}", String.valueOf({{paramName}}));
+      queryParams.put("{{baseName}}", ApiInvoker.parameterToString({{paramName}}));
     {{/queryParams}}
-    {{#headerParams}}headerParams.put("{{baseName}}", {{paramName}});
+    {{#headerParams}}headerParams.put("{{baseName}}", ApiInvoker.parameterToString({{paramName}}));
     {{/headerParams}}
     String[] contentTypes = {
       {{#consumes}}"{{mediaType}}"{{#hasMore}},{{/hasMore}}{{/consumes}}
@@ -74,7 +74,7 @@ public class {{classname}} {
       FormDataMultiPart mp = new FormDataMultiPart();
       {{#formParams}}{{#notFile}}
       hasFields = true;
-      mp.field("{{baseName}}", {{paramName}}, MediaType.MULTIPART_FORM_DATA_TYPE);
+      mp.field("{{baseName}}", ApiInvoker.parameterToString({{paramName}}), MediaType.MULTIPART_FORM_DATA_TYPE);
       {{/notFile}}{{#isFile}}
       hasFields = true;
       mp.field("{{baseName}}", {{paramName}}, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -83,7 +83,7 @@ public class {{classname}} {
         postBody = mp;
     }
     else {
-      {{#formParams}}{{#notFile}}formParams.put("{{baseName}}", {{paramName}});{{/notFile}}
+      {{#formParams}}{{#notFile}}formParams.put("{{baseName}}", ApiInvoker.parameterToString({{paramName}}));{{/notFile}}
       {{/formParams}}
     }
 

modules/swagger-codegen/src/main/resources/Java/apiInvoker.mustache

@@ -19,16 +19,75 @@ import javax.ws.rs.core.MediaType;
 import java.util.Map;
 import java.util.HashMap;
 import java.util.List;
-import java.io.IOException;
+import java.util.Date;
+import java.util.TimeZone;
+
 import java.net.URLEncoder;
+
+import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 
+import java.text.SimpleDateFormat;
+import java.text.ParseException;
+
 public class ApiInvoker {
   private static ApiInvoker INSTANCE = new ApiInvoker();
   private Map<String, Client> hostMap = new HashMap<String, Client>();
   private Map<String, String> defaultHeaderMap = new HashMap<String, String>();
   private boolean isDebug = false;
 
+  /**
+   * ISO 8601 date time format.
+   * @see https://en.wikipedia.org/wiki/ISO_8601
+   */
+  public static final SimpleDateFormat DATE_TIME_FORMAT = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssXXX");
+
+  /**
+   * ISO 8601 date format.
+   * @see https://en.wikipedia.org/wiki/ISO_8601
+   */
+  public static final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd");
+
+  static {
+    // Use UTC as the default time zone.
+    DATE_TIME_FORMAT.setTimeZone(TimeZone.getTimeZone("UTC"));
+    DATE_FORMAT.setTimeZone(TimeZone.getTimeZone("UTC"));
+  }
+
+  public static Date parseDateTime(String str) {
+    try {
+      return DATE_TIME_FORMAT.parse(str);
+    } catch (java.text.ParseException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  public static Date parseDate(String str) {
+    try {
+      return DATE_FORMAT.parse(str);
+    } catch (java.text.ParseException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  public static String formatDateTime(Date datetime) {
+    return DATE_TIME_FORMAT.format(datetime);
+  }
+
+  public static String formatDate(Date date) {
+    return DATE_FORMAT.format(date);
+  }
+
+  public static String parameterToString(Object param) {
+    if (param == null) {
+      return "";
+    } else if (param instanceof Date) {
+      return formatDateTime((Date) param);
+    } else {
+      return String.valueOf(param);
+    }
+  }
+
   public void enableDebug() {
     isDebug = true;
   }