package com.test;



import java.io.IOException;

import java.io.StringReader;



import javax.servlet.FilterChain;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;



import org.codehaus.jackson.map.DeserializationConfig;

import org.codehaus.jackson.map.ObjectMapper;

import org.junit.Assert;

import org.junit.Test;

import org.springframework.mock.web.MockFilterChain;

import org.springframework.mock.web.MockFilterConfig;

import org.springframework.mock.web.MockHttpServletRequest;

import org.springframework.mock.web.MockHttpServletResponse;



public class ErrorHandlerMockTest {



        @Test

        public void testDoFilter() throws ServletException, IOException {

                MockHttpServletRequest request = new MockHttpServletRequest();

                MockHttpServletResponse response = new MockHttpServletResponse();

                MockFilterConfig config = new MockFilterConfig();

                

                FilterChain filterChain = new MockFilterChain() {

                        @Override

                        public void doFilter(ServletRequest req, ServletResponse res) {

                                throw new NullPointerException("test Filter");

                        }

                };

                

                ErrorHandler filter = new ErrorHandler();

                filter.init(config);

                filter.doFilter(request, response, filterChain);

                

                String contentAsString = response.getContentAsString();

                ObjectMapper mapper = new ObjectMapper();

                mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    

// ResponseInfo object is the custom object which will be returned as json response in filters

                ResponseInfo responseInfo = mapper.readValue(new StringReader(contentAsString), ResponseInfo.class);
    

                String errorCode = responseInfo.getResponseCode();

                Assert.assertEquals("ERR_CODE_000000", errorCode);

        }



}


Ref : http://kaleeswaran14.blogspot.in/2014/01/filters-to-handle-errors-in-application.html