{"id":2958,"date":"2011-02-07T10:06:07","date_gmt":"2011-02-07T09:06:07","guid":{"rendered":"http:\/\/blog.jteam.nl\/?p=2958"},"modified":"2011-02-07T10:06:07","modified_gmt":"2011-02-07T09:06:07","slug":"creating-an-android-app-for-your-website-with-spring-android-and-rest","status":"publish","type":"post","link":"https:\/\/trifork.nl\/blog\/creating-an-android-app-for-your-website-with-spring-android-and-rest\/","title":{"rendered":"Creating an Android app for your website with Spring Android and REST"},"content":{"rendered":"

As Android is really hot at the moment (and I have an Android phone), I wanted to create an Android app for my website. In this blog post I will explain the changes I had to make on the part of my web application and how I used Spring Android to interact from Android to my web application.<\/p>\n

<\/p>\n

Website<\/h2>\n

My website is just a simple Spring application with Spring MVC 3.0.5, JPA, Hibernate and MySQL. In order to create a REST api that is understandable for my Android app, I needed to add a little more configuration to the web application.<\/p>\n

Spring Security<\/h3>\n

As I have Spring Security in place, I had to add a security rule for my REST api. If you really want to do it the right way, than make sure you use the OAuth<\/a> implementation as Spring Android also provides you to use OAuth in your Android app.<\/p>\n

But being a bit lazy I just configured the REST api to be public and therefor does not require any authentication. This is good for now.<\/p>\n

So in my security-context.xml I added the following rule:<\/p>\n

<br>\n<intercept-url access="hasRole('ROLE_ANONYMOUS')" pattern="\/rest\/**"><br>\n<\/pre><\/p>\n
As you can see I specified all the URL\u2019s that match on \/rest\/**<\/span> can be accessed without any authentication.<\/p>\n
ContentNegotiatingViewResolver<\/h3>\n
Spring provides us with the ContentNegotiatingViewResolver<\/a>. This is an implementation of ViewResolver that resolves a view based on the file extension, parameter, or Accept header.<\/p>\n
<br>\n    <bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">\n        <property name="mediaTypes">\n<map>\n                <entry value="application\/json" key="json"><br>\n                <entry value="text\/html" key="html"><br>\n            <\/entry><\/entry><\/map>\n<\/property><\/bean><\/p><p>\n        <property name="viewResolvers">\n<list>\n                <bean class="org.springframework.web.servlet.view.UrlBasedViewResolver">\n                    <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"><\/property>\n                    <property name="prefix" value="\/WEB-INF\/jsp\/"><\/property>\n                    <property name="suffix" value=".jsp"><\/property>\n                <\/bean>\n            <\/list>\n        <\/property>\n        <property name="defaultViews">\n<list>\n                <bean class="org.springframework.web.servlet.view.json.MappingJacksonJsonView">\n            <\/bean><\/list>\n        <\/property>\n    <br>\n<\/pre><\/p>\n
As you can see in the code above, I have configured two mediaTypes<\/span>. The json<\/span> mediatype will be used by our Android app and the html<\/span> mediatype will be used by any browser.<\/p>\n
The defaultViews<\/span> property allows us to override the views provided by the view resolvers. Which is necessary in order resolve the correct view for JSON.<\/p>\n
Converting data<\/h3>\n
Later on this post I will show how you can POST data to your controllers via Spring Android. To do this we need to configure the MappingJacksonHttpMessageConverter<\/a><\/span> that allows us to convert data of  the media type application\/json<\/span>.<\/p>\n
<br>\n    <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">\n        <property name="messageConverters">\n<list>\n                <ref bean="jsonConverter">\n            <\/ref><\/list>\n        <\/property>\n    <\/bean><\/p>\n<p>    <bean id="jsonConverter" class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">\n        <property name="supportedMediaTypes" value="application\/json"><\/property>\n    <\/bean><br>\n<\/pre><\/p>\n
Controller<\/h3>\n
Now that we have the ContentNegotiatingViewResolver in place, we can call any URL in our web application with the .json<\/span> extension and give you a JSON representation of your data. Let\u2019s take a look at an example of a Controller method.<\/p>\n
<br>\n    @RequestMapping("\/rest\/matches\/played")<br>\n    public ModelAndView getAllPlayedMatches() {<br>\n        Competition competition = competitionService.findCompetitionByDescription(CURRENT_COMPETITION_DESCRIPTION);<br>\n        List<match> matches = matchService.getAllMatchesByCompetitionAndStatusDesc(competition, true);<\/match><\/p>\n<p>        List<matchdto> matchesDto = getMatches(matches);<\/matchdto><\/p>\n<p>        ModelAndView mav = new ModelAndView();<br>\n        mav.addObject("matches", matchesDto);<br>\n        return mav;<br>\n    }<br>\n<\/pre><\/p>\n
If I want to call this method via my browser, I can simple call \/rest\/matches\/played.json. This will simply work for all your request mappings. In this example I convert the list of matches to a list of matchDto objects. These objects contain less data, so that I don\u2019t send any unnecessary data to our Android app.<\/p>\n
The JSON output will look like this:<\/p>\n
{<br>\n   "matches": [<br>\n    {<br>\n        "id": 125,<br>\n        "comment": "Match nr 137667",<br>\n        "date": "2 february 2011 at 21:05",<br>\n        "home_team": "VVGA 2",<br>\n        "away_team": "Badhoevedorp 2",<br>\n        "home_goals": 6,<br>\n        "away_goals": 9,<br>\n        "location": "Zuid"<br>\n    }, <\/p>\n<p>    {<br>\n        "id": 124,<br>\n        "comment": "Match nr 137684",<br>\n        "date": "26 january 2011 at 20:15",<br>\n        "home_team": "DCG 7",<br>\n        "away_team": "VVGA 2",<br>\n        "home_goals": 7,<br>\n        "away_goals": 4,<br>\n        "location": "Zuid"<br>\n    }<br>\n..<br>\n}<br>\n<\/pre><\/p>\n
Well that\u2019s basically it for the web application part. I have created separate controllers for my REST api, but you could easily reuse your existing controller if it contains all your data.<\/p>\n
Android app<\/h2>\n
Spring Android<\/h3>\n
Spring Android<\/a> provides us with a Rest Client<\/a> and Commons Logging<\/a> adapter for Android. I don\u2019t want to spend any time on how to set-up an Android project, as everyone prefers their own IDE. But it is clear that we need the Spring Android jars in our project.<\/p>\n
You can either download<\/a> them from the Spring Android site of you can use Maven<\/a> to include them into your project.<\/p>\n
RestTemplate – GET<\/h3>\n
Retrieving data from our web application is really simple thanks to the RestTemplate.<\/p>\n
<br>\npublic Matches getPlayedMatches() {<br>\n    RestTemplate restTemplate = new RestTemplate();<br>\n    restTemplate.setRequestFactory(new CommonsClientHttpRequestFactory());<br>\n    String url = BASE_URL + "\/rest\/matches\/played.json";<br>\n    return restTemplate.getForObject(url, Matches.class);<br>\n}<br>\n<\/pre><\/p>\n
The code above uses the getForObject()<\/span> method to invoke the REST api from our web application and expects an object of the type Matches<\/span>. This object contains an array of Match<\/span> objects. The Match<\/span> object contains all fields that are present in the JSON output.<\/p>\n
RestTemplate \u2013 POST<\/h3>\n
Posting data to our web application is as easy as retrieving data.<\/p>\n
<br>\npublic boolean getUser(String username, String password) {<br>\n    String url = BASE_URL + "\/rest\/login.json";<\/p>\n<p>    Credentials credentials = new Credentials(username, password);<br>\n    return restTemplate.postForObject(url, credentials, Boolean.class);<br>\n}<br>\n<\/pre><\/p>\n
You can just use the postForObject()<\/span> method to POST any object to your web application. In this example I post a Credentials<\/span> object which contains the username and password. This is not really secure, but fits it\u2019s purpose for now.<\/p>\n
@RequestBody and @ResponseBody<\/h3>\n
One thing that I want to mention is the use of @RequestBody<\/span> and @ResponseBody<\/span> in a controller in the web application part. In my web application I have the exact same Credentials<\/span> object as in my Android app. This allows us to use the following controller code:<\/p>\n
<br>\n@RequestMapping(value = "\/rest\/login", method = RequestMethod.POST)<br>\npublic @ResponseBody boolean login(@RequestBody Credentials credentials) {<br>\n    String username = credentials.getUsername();<br>\n    String password = credentials.getPassword();<\/p>\n<p>    boolean isValidUser = \/\/ check if user exist.<\/p>\n<p>    return isValidUser;<br>\n}<br>\n<\/pre><\/p>\n
Because of the jsonConverter<\/span> we configured earlier, the object in the request is mapped to the Credentials<\/span> object in the web application.<\/p>\n
With @ResponseBody<\/span> I directly bind my method return value to the web response body. So there is no need for creating a model and as you could see in the corresponding Android part I can just expect a boolean<\/span> to be returned.<\/p>\n
Next time<\/h2>\n
Now that we are able to communicate from an Android app to a web application and vice versa, it is time to create a great Android app. In my next blog post I will explain how I applied a few layout patterns<\/a> and Android how I tackled a few of my problems during the development of my Android app.<\/p>\n\n\n
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As Android is really hot at the moment (and I have an Android phone), I wanted to create an Android app for my website. 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