Software Engineering 2 A practical course in software engineering. Ekkart Kindler

Transcription

1 Software Engineering 2 A practical course in software engineering

2 Tutorial 2: Consuming REST Services

3 Contens How to consume REST services Example: NorthQ standalone Java application (but can be re-used later for OpenHAB bindings) Userfull frameworks And how to integrate the technically Development stragtegies 3

4 Development Strategies Look at API documentation Which services might be relevant for your purpose? What parameters do the take? What results do they produce? Manually run through the sequence of calls to Test idea Check exact parameters Other config options (headers, authentication,...) Invokation methods Inspect returned results 4

5 Tools Tools for manual testing REST APIs curl: Command line tool for issuing data transfer commands Postman: Tool chain for developing REST APIs; graphical GUI for REST clients Many other tools 5

6 HttpRequester (Firefox) 6

7 Development Strategies Look at API documentation Manually run through the sequence of calls Only after you did that, program the REST clients: There are different frameworks for that Apache CXF: Jersey: Spring: Retrofit: 7

8 Implementaion In the following, we use the JAX-RS: Java API for RESTful Web services with Jersey (a reference implementation) and Jackson (for behind the scenes conversion between JSON and POJOs) 8

9 Maven dependencies <dependency> <groupid>javax.ws.rs</groupid> <artifactid>javax.ws.rs-api</artifactid> <version>release</version> </dependency> <dependency> <groupid>org.glassfish.jersey.core</groupid> <artifactid>jersey-client</artifactid> <version>release</version> </dependency> <dependency> <groupid>org.glassfish.jersey.inject</groupid> <artifactid>jersey-hk2</artifactid> <version>release</version> </dependency> <dependency> <groupid>org.glassfish.jersey.media</groupid> <artifactid>jersey-media-json-jackson</artifactid> <version>release</version> </dependency> 9

10 Practical steps In your Eclipse (openhab installation) create a new Java project for the NorthQStandaloneApp Create a class with a main method On right-click on the project Via Configure Convert to Maven Project, convert your project to a Maven project Check that you have a pom.xml file in the project and add the above dependencies as dependencies to the pom.xml file of your project. By a right-click on pom.xml run a maven build with goals clean and package 10

11 Code snippets Form form = new Form(); form.param("username", username); form.param("password", password); Client client = ClientBuilder.newClient(); username and password should also better be defined as constants. Builder builder = client.target(northq_new_token_url). request(mediatype.application_json); String result = builder.post( Entity.entity(form, MediaType.APPLICATION_FORM_URLENCODED_TYPE), String.class); 11

12 Code snippets (cntd.)... Client client = ClientBuilder.newClient().register(JacksonFeature.class); Response result = builder.post( Entity.entity(form, MediaType.APPLICATION_FORM_URLENCODED_TYPE), Response.class); Map<?,?> map = result.readentity(map.class); for (Object key : map.keyset()) { System.out.println(key + ": " + map.get(key)); } Result is converted to a Map (only possible with Jackson installed) 12

13 Code snippets (cntd.)... Client client = ClientBuilder.newClient().register(JacksonFeature.class); Response result = builder.post( Entity.entity(form, MediaType.APPLICATION_FORM_URLENCODED_TYPE), Response.class); TokenInfo tokeninfo = result.readentity(tokeninfo.class); Result is converted to a TokenInfo object (only possible with Jackson installed) 13

14 Code snippets (cntd.) public class TokenInfo { public String token; public String user; public boolean success; public String errors; Would be nicer with private attributes and getters and setters, but also works this way. public String tostring() { if (success) { return "Token: id='" + token + "'" + " user='" + user + "'"; } else { return "Token (fail): error='" + errors + "'"; } } 14

15 Code snippets (cntd.)... Client client = ClientBuilder.newClient().register(JacksonFeature.class); TokenInfo token = builder.post( Entity.entity(form, MediaType.APPLICATION_FORM_URLENCODED_TYPE), TokenInfo.class); Result is a TokenInfo object without an intermediate Result object (only possible with Jackson installed) 15

16 Code snippets (cntd.)... WebTarget target = client.target(northq_user_houses_url); List<Map<?,?>> houses = target.queryparam(northq_user_param, tokeninfo.user). queryparam(northq_token_param, tokeninfo.token). request(mediatype.application_json). get(list.class); A get request (with automatic conversion to a list); not that this is not type safe 16