diff --git a/modules/swagger-codegen/src/main/java/com/wordnik/swagger/codegen/DefaultCodegen.java b/modules/swagger-codegen/src/main/java/com/wordnik/swagger/codegen/DefaultCodegen.java
index bcbd71f3741..0aae418b83d 100644
--- a/modules/swagger-codegen/src/main/java/com/wordnik/swagger/codegen/DefaultCodegen.java
+++ b/modules/swagger-codegen/src/main/java/com/wordnik/swagger/codegen/DefaultCodegen.java
@@ -621,6 +621,8 @@ public class DefaultCodegen {
         count += 1;
         if (count < operation.getConsumes().size())
           mediaType.put("hasMore", "true");
+        else
+          mediaType.put("hasMore", null);
         c.add(mediaType);
       }
       op.consumes = c;
@@ -636,6 +638,8 @@ public class DefaultCodegen {
         count += 1;
         if (count < operation.getProduces().size())
           mediaType.put("hasMore", "true");
+        else
+          mediaType.put("hasMore", null);
         c.add(mediaType);
       }
       op.produces = c;
diff --git a/modules/swagger-codegen/src/main/resources/Java/api.mustache b/modules/swagger-codegen/src/main/resources/Java/api.mustache
index 4a1ab1dc77b..ad26268d715 100644
--- a/modules/swagger-codegen/src/main/resources/Java/api.mustache
+++ b/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}}
     }
 
diff --git a/modules/swagger-codegen/src/main/resources/Java/apiInvoker.mustache b/modules/swagger-codegen/src/main/resources/Java/apiInvoker.mustache
index 26379c60105..9a8ac94baec 100644
--- a/modules/swagger-codegen/src/main/resources/Java/apiInvoker.mustache
+++ b/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;
   }
diff --git a/samples/client/petstore/java/src/main/java/io/swagger/client/ApiInvoker.java b/samples/client/petstore/java/src/main/java/io/swagger/client/ApiInvoker.java
index 966a141c03d..abe51bb7106 100644
--- a/samples/client/petstore/java/src/main/java/io/swagger/client/ApiInvoker.java
+++ b/samples/client/petstore/java/src/main/java/io/swagger/client/ApiInvoker.java
@@ -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;
   }
diff --git a/samples/client/petstore/java/src/main/java/io/swagger/client/api/PetApi.java b/samples/client/petstore/java/src/main/java/io/swagger/client/api/PetApi.java
index 53c1d55fb68..686deae12ea 100644
--- a/samples/client/petstore/java/src/main/java/io/swagger/client/api/PetApi.java
+++ b/samples/client/petstore/java/src/main/java/io/swagger/client/api/PetApi.java
@@ -148,8 +148,8 @@ public class PetApi {
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
-    if(!"null".equals(String.valueOf(status)))
-      queryParams.put("status", String.valueOf(status));
+    if (status != null)
+      queryParams.put("status", ApiInvoker.parameterToString(status));
     
     
     String[] contentTypes = {
@@ -200,8 +200,8 @@ public class PetApi {
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
-    if(!"null".equals(String.valueOf(tags)))
-      queryParams.put("tags", String.valueOf(tags));
+    if (tags != null)
+      queryParams.put("tags", ApiInvoker.parameterToString(tags));
     
     
     String[] contentTypes = {
@@ -317,17 +317,17 @@ public class PetApi {
       FormDataMultiPart mp = new FormDataMultiPart();
       
       hasFields = true;
-      mp.field("name", name, MediaType.MULTIPART_FORM_DATA_TYPE);
+      mp.field("name", ApiInvoker.parameterToString(name), MediaType.MULTIPART_FORM_DATA_TYPE);
       
       hasFields = true;
-      mp.field("status", status, MediaType.MULTIPART_FORM_DATA_TYPE);
+      mp.field("status", ApiInvoker.parameterToString(status), MediaType.MULTIPART_FORM_DATA_TYPE);
       
       if(hasFields)
         postBody = mp;
     }
     else {
-      formParams.put("name", name);
-      formParams.put("status", status);
+      formParams.put("name", ApiInvoker.parameterToString(name));
+      formParams.put("status", ApiInvoker.parameterToString(status));
       
     }
 
@@ -364,7 +364,7 @@ public class PetApi {
     Map<String, String> formParams = new HashMap<String, String>();
 
     
-    headerParams.put("api_key", api_key);
+    headerParams.put("api_key", ApiInvoker.parameterToString(api_key));
     
     String[] contentTypes = {
       
@@ -428,7 +428,7 @@ public class PetApi {
       FormDataMultiPart mp = new FormDataMultiPart();
       
       hasFields = true;
-      mp.field("additionalMetadata", additionalMetadata, MediaType.MULTIPART_FORM_DATA_TYPE);
+      mp.field("additionalMetadata", ApiInvoker.parameterToString(additionalMetadata), MediaType.MULTIPART_FORM_DATA_TYPE);
       
       hasFields = true;
       mp.field("file", file, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -437,7 +437,7 @@ public class PetApi {
         postBody = mp;
     }
     else {
-      formParams.put("additionalMetadata", additionalMetadata);
+      formParams.put("additionalMetadata", ApiInvoker.parameterToString(additionalMetadata));
       
       
     }
diff --git a/samples/client/petstore/java/src/main/java/io/swagger/client/api/UserApi.java b/samples/client/petstore/java/src/main/java/io/swagger/client/api/UserApi.java
index 2da4c6ae32e..7b8b2cad83a 100644
--- a/samples/client/petstore/java/src/main/java/io/swagger/client/api/UserApi.java
+++ b/samples/client/petstore/java/src/main/java/io/swagger/client/api/UserApi.java
@@ -198,10 +198,10 @@ public class UserApi {
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
-    if(!"null".equals(String.valueOf(username)))
-      queryParams.put("username", String.valueOf(username));
-    if(!"null".equals(String.valueOf(password)))
-      queryParams.put("password", String.valueOf(password));
+    if (username != null)
+      queryParams.put("username", ApiInvoker.parameterToString(username));
+    if (password != null)
+      queryParams.put("password", ApiInvoker.parameterToString(password));
     
     
     String[] contentTypes = {