[FIXED] Having trouble getting response from REST request - Java NetBeans with Spring Beans

Issue

I am trying to learn how to do REST services with Spring in NetBeans with Java.

In my application I created a bean and put in the dependencies in my pom.xml file.

When i make my request (which I know works when i enter it in a browser and get back JSON), i get the following error:

--- exec-maven-plugin:1.2.1:exec (default-cli) @ AutoNGplusAPITest ---
Exception in thread "AWT-EventQueue-0" org.springframework.web.client.RestClientException: Could not extract response: no suitable HttpMessageConverter found for response type [interface java.util.Map] and content type [text/html;charset=utf-8]
    at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:108)
    at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:773)
    at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:758)
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:535)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:489)
    at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:431)
    at com.blackstonesoftwaretechnologies.startPage.sendURIActionPerformed(startPage.java:467)
    at com.blackstonesoftwaretechnologies.startPage.access$800(startPage.java:26)
    at com.blackstonesoftwaretechnologies.startPage$9.actionPerformed(startPage.java:218)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6533)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
    at java.awt.Component.processEvent(Component.java:6298)
    at java.awt.Container.processEvent(Container.java:2236)
    at java.awt.Component.dispatchEventImpl(Component.java:4889)
    at java.awt.Container.dispatchEventImpl(Container.java:2294)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
    at java.awt.Container.dispatchEventImpl(Container.java:2280)
    at java.awt.Window.dispatchEventImpl(Window.java:2746)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:731)
    at java.awt.EventQueue$4.run(EventQueue.java:729)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
------------------------------------------------------------------------
BUILD SUCCESS
------------------------------------------------------------------------
Total time: 19.966s
Finished at: Wed Sep 14 11:15:07 EDT 2016
Final Memory: 6M/106M

---

Here is the code in my Java class file that I am running which passes the REST call:

private void sendURIActionPerformed(java.awt.event.ActionEvent evt) {                                        
        // TODO add your handling code here:
        String link, api = null;
        link = parseString(endpointAPI.getText());
        shortResults.setText("URI under Test is: " + String.valueOf(link) + ". \n" + "Please wait ..." + "\n\n\n" + "Results: " + "\n");
        //api = parseString(endpointAPI.getText());

        Object[] row = {link, "", "200", ""};
        DefaultTableModel model = (DefaultTableModel) parameterTable.getModel();
        model.addRow(row);

        RestTemplate restTemplate = new RestTemplate();
        HttpHeaders requestHeaders = new HttpHeaders();

        requestHeaders.add("Content-Type","application/json");

        HttpEntity<String> request = new HttpEntity<>(requestHeaders);

        String tokenaccess = "";
        String apiUndertest1 = restTemplate.exchange(link, HttpMethod.GET, request, String.class).getBody();
        Map result = restTemplate.exchange(link, HttpMethod.GET, request, Map.class).getBody();

        shortResults.append(apiUndertest1);

    }                                       

What am i missing? I was assuming that in the pom.xml file, the spring dependencies that I downloaded would take care of the JSON conversion.

The sample urls I am using are: https://github.com and http://jsonplaceholder.typicode.com/posts/1

Can someone help me understand where I made my mistake and show me how to correct it (missing code, code structure, etc). I really want to learn this correctly.

Thanks

Solution

Spring rest template does not automatically map JSON to objects. You have to explicitly define it. Use Jackson(core, databind, annotations). Put below in dispatcher servlet:

<beans:bean
        class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
        <beans:property name="messageConverters">
            <beans:list>
                <beans:ref bean="jsonMessageConverter" />
            </beans:list>
        </beans:property>
    </beans:bean>

    <!-- Configure bean to convert JSON to POJO and vice versa -->
    <beans:bean id="jsonMessageConverter"
        class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
    </beans:bean>

This will take care of converting JSON to Class objects and vice versa.

This should ideally do the trick.

Answered By - HARDI