---
title:  Prerequisites and Limitations for Writing REST Applications
---

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Before development, it is important to understand the prerequisites and limitations of the <%=vars.product_name%> REST implementation.

<%=vars.product_name%> and REST-enabled applications accessing <%=vars.product_name%> are subject to the following rules and limitations:

-   All domain objects, functions and function-arg classes must be properly configured and registered in the <%=vars.product_name%> deployment. Any functions that you wish to execute through the REST API must be available on the target member’s CLASSPATH.
-   The current implementation supports only the **application/json** MIME type. Other return types (XML, objects, and so on) are not supported. Plain text is supported as a return type for some error messages.
-   Keys are strictly of type String. For example, the request `PUT http://localhost:8080/gemfire-api/v1/customers/123.456` will add an entry for key ("123.456") of type String.
-   Some special formats of JSON documents are not supported in <%=vars.product_name%> REST. See [Key Types and JSON Support](troubleshooting.html#concept_gsv_zd5_m4) for examples.
-   To achieve interoperability between <%=vars.product_name%> Java clients (or <%=vars.product_name%> native clients) and REST clients, the following rules must be followed:
    -   All <%=vars.product_name%> Java and native client classes operating on data also accessed by the REST interface must be PDX serialized, either via PDX autoserialization or by implementing `PdxSerializable`.
    -   <%=vars.product_name%> Java clients and native clients can retrieve REST-enabled data either as a `PdxInstance` or as an actual object by using the `PdxInstance.getObject` method. If you use the latter method, you must first declare the object type (@type) in your POST or PUT request payload when creating the object in REST; and secondly, the Java client must have the actual domain class in its CLASSPATH.
-   Objects returned by REST-invoked functions must be returned as PdxInstance objects or other data types that can be written to JSON. You cannot return Java objects.
-   REST client applications do not support single hop access or notification features.
-   Specifying subregions as endpoints is not supported.


