Rex Young's Blog

How to bind front-end JSON strings to back-end Spring beans?

    KEY            VALUE
    ---            -----
    employee       {firstName:"F",lastName:"L",address:["street","town","state"],ssn:123456789}

    KEY                    VALUE
    ---                    -----
    employee.firstName     F
    employee.lastName      L
    employee.address[0]    street
    employee.address[1]    town
    employee.address[2]    state
    employee.ssn           123456789

public class JsonAwareDispatcherServlet extends DispatcherServlet {
    @Override
    protected void doService(HttpServletRequest request, HttpServletResponse response)
            throws Exception {
        if (JsonAwareHttpServletRequest.jsonInside(request)) {
            super.doService(new JsonAwareHttpServletRequest(request), response);
        } else {
            super.doService(request, response);
        }
    }
}

public class JsonAwareHttpServletRequest extends HttpServletRequestWrapper {

    private Map springParamMap;

    public JsonAwareHttpServletRequest(HttpServletRequest request) {
        super(request);

        springParamMap = convertJsonParameters(request.getParameterMap());
    }

    @Override
    public String getParameter(String name) {
        String[] values = springParamMap.get(name);
        if (values == null || values.length == 0) {
            return null;
        } else {
            return values[0];
        }
    }

    @Override
    public String[] getParameterValues(String name) {
        return springParamMap.get(name);
    }

    @Override
    public Map getParameterMap() {
        return springParamMap;
    }

    @Override
    public Enumeration getParameterNames() {
        return Collections.enumeration(springParamMap.keySet());
    }

    static protected Map convertJsonParameters(Map jsonParamMap) {
        HashMap resultMap = new HashMap();
        HashMap workMap = new HashMap();

        for (Map.Entry entry : jsonParamMap.entrySet()) {
            String name = entry.getKey();
            String[] values = entry.getValue();

            if (JsonBinderUtils.isJson(values)) {
                JsonBinderUtils.convertJsonString(workMap, name, values);

                for (Map.Entry workEntry : workMap.entrySet()) {
                    resultMap.put(workEntry.getKey(), new String[] { workEntry.getValue() });
                }

                workMap.clear();
            } else {
                resultMap.put(name, values);
            }
        }

        return resultMap;
    }

    static public boolean jsonInside(HttpServletRequest request) {
        if (request instanceof JsonAwareHttpServletRequest) {
            return false;
        }

        Collection valuesForAllKeys = request.getParameterMap().values();

        for (String[] valuesPerKey : valuesForAllKeys) {
            if (JsonBinderUtils.isJson(valuesPerKey)) {
                return true;
            }
        }

        return false;
    }
}

public class JsonBinderUtils {

    static public void convertJsonString(Map resultMap, String name, String[] values) {
        if (values.length == 1) {
            convertJsonString(resultMap, name, values[0]);
        } else {
            for (int i = 0; i < values.length; i++) {
                convertJsonString(resultMap, name + "[" + i + "]", values[i]);
            }
        }
    }

    static public void convertJsonString(Map resultMap, String name, String value) {
        if (!isJson(value)) {
            resultMap.put(name, value);
            return;
        }

        ArrayList resultList = new ArrayList();
        LinkedList jsonList = new LinkedList();

        if (isJsonObject(value)) {
            jsonList.add(new PropertyValue(name, JSONObject.fromObject(value)));
        } else if (isJsonArray(value)) {
            jsonList.add(new PropertyValue(name, JSONArray.fromObject(value)));
        }

        convertJsonObject(resultList, jsonList);

        for (PropertyValue pv : resultList) {
            resultMap.put(pv.getName(), (String) pv.getValue());
        }
    }

    @SuppressWarnings("unchecked")
    static protected void convertJsonObject(List resultList,
            LinkedList jsonList) {
        while (jsonList.size() > 0) {
            PropertyValue pv = jsonList.poll();
            String name = pv.getName();

            if (pv.getValue() instanceof JSONObject) {
                JSONObject jsonObject = (JSONObject) pv.getValue();

                if (jsonObject.isNullObject()) {
                    continue;
                }

                Set> entrySet = jsonObject.entrySet();

                for (Map.Entry entry : entrySet) {
                    String pvName = name + "." + entry.getKey();
                    Object pvValue = entry.getValue();

                    if (pvValue instanceof JSONObject || pvValue instanceof JSONArray) {
                        jsonList.addLast(new PropertyValue(pvName, pvValue));
                    } else {
                        resultList.add(new PropertyValue(pvName, pvValue.toString()));
                    }
                }
            } else if (pv.getValue() instanceof JSONArray) {
                JSONArray jsonArray = (JSONArray) pv.getValue();

                for (int i = 0; i < jsonArray.size(); i++) {
                    String pvName = name + "[" + i + "]";
                    Object pvValue = jsonArray.get(i);

                    if (pvValue instanceof JSONObject || pvValue instanceof JSONArray) {
                        jsonList.addLast(new PropertyValue(pvName, pvValue));
                    } else {
                        resultList.add(new PropertyValue(pvName, pvValue.toString()));
                    }
                }
            }
        }
    }

    static public boolean isJsonObject(String value) {
        return value != null && (value.startsWith("{") && value.endsWith("}"));
    }

    static public boolean isJsonArray(String value) {
        return value != null && (value.startsWith("[") && value.endsWith("]"));
    }


    static public boolean isJson(String value) {
        return isJsonObject(value) || isJsonArray(value);
    }

    static public boolean isJson(String[] valueArray) {
        if (valueArray.length == 0) {
            return false;
        }

        int jsonObjectCount = 0;
        int jsonArrayCount = 0;

        for (String value : valueArray) {
            if (isJsonObject(value)) {
                jsonObjectCount++;
            } else if (isJsonArray(value)) {
                jsonArrayCount++;
            }
        }

        return (jsonObjectCount == valueArray.length || jsonArrayCount == valueArray.length);
    }

}

Comments

• It's an interesting approach. I worked on an alternate approach that leverages JAX-RS, JAXB and Jetty. I added an integration that will allow you to either create "Controllers" using JAX-RS, which implicitly do incoming and outgoing JSon conversion (among other things). You can also add an annotation to existing Spring 2.5 annotated controllers, plus some configuration, that will allow you to do something like:

  @RequestMapping(...POST)
  public void processData(@RestfulData("application/json") MyObject myObject){
  // do something with myObject
  }

  Keep an eye out for it in the next release of JBoss Resteasy (beta9).

  The Spring guys are also working on RESTifying the MVC framework in Spring 3.0, which should include similar functionality.

  Posted by: sduskis on November 21, 2008 at 11:17 AM

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