Making applica+ons with Java. Text Technologies 2013 Chris Culy

Transcription

1 Making applica+ons with Java

2 Desktop applica+on aka executable jar file Commandline: java jar myapplica+on.jar Or, if you have a GUI interface, doubleclick on the jar file Easiest solu+on: Let the IDE do it for you e.g. Netbeans New Project Java - > JavaApplica+on OR Maven - > JavaApplica+on

3 Do it yourself executable jar (1) h\p://docs.oracle.com/javase/tutorial/deployment/jar/basicsindex.html h\p://docs.oracle.com/javase/tutorial/deployment/jar/manifes+ndex.html Need a MANIFEST file which says What the main class is Where the classpath is for external classes (jars)

4 Do it yourself executable jar (2) Create a text file that has these two lines Main- Class: full package and class name Class- Path: rela0ve path to other jars The file must end with newline or carriage return Omit Class- Path if there are no external classes/jars

5 Do it yourself executable jar (3) Build your project You can extract the default MANIFEST like this: jar xvf myjar.jar META- INF/MANIFEST.MF Update the MANIFEST with the correct informa+on from the text file jar ufm myjar.jar pathtoinfofile Now you can run your program from the commandline java jar myjar.jar

6 Web applica+ons 2 common approaches (not just in Java) Web page templates combined with code Java Server Pages (JSP); ASP, PHP, etc. Web page + Web services

7 JSP (1) h\p:// An IDE makes this much easier It will set up a test server for you (e.g. Tomcat) E.g. Netbeans: Make New Project - > Java Web - > Web Applica+on NB: Need Java EE, Web tools

8 JSP basics Expression: <%= java_expression %> java_expression is evaluated (once) when the page loads and subs+tuted in the html Scriptlet: <% java_code %> java_code is evaluated, but not subs+tuted To insert a value into the page, use: out.println(...) Direc+ve: <%@ page... %> At the top, used e.g. for import <%@ page import="java.u+l.*,java.text.*" %>

9 JSP and Java classes (1) h\ps://netbeans.org/kb/docs/web/quickstart- webapps.html h\p:// We can use classes in a JSP page Simple beans can do things with proper+es, e.g. from forms Other classes can do whatever we want But: everything is evaluated when we load the page

10 JSP and Java classes (2) We can use classes in scriptlets as we normally would Need to import the class in the page... %> direc+ve

11 JSP, bean classes and forms (1) Beans are a special conven+onalized class Bean needs a no- argument constructor Any fields (instance variables) we want to access, need to have a ge\er and a se\er of the forms: type getvariablename() void setvariablename(type valname) Where the field/variable is variablename Note the capitaliza+on in getx, setx We can have other public and private func+ons as well

12 JSP, bean classes and forms (2) To use a bean with a form, In the form, set the handler jsp page as the ac+on <form name="name Input Form" ac+on="response.jsp"> The name a\ributes of the form input elements must correspond to the fields in the bean e.g. for <input type="text" name="name" /> We would have a field name, with getname() and setname()

13 JSP, bean classes and forms (3) To use a bean with a form, In the handler jsp page At the top of the body, add <jsp:usebean id="beannameinpage" scope="session" class="packageandnameofbean" /> NB: this works for any bean, not just ones for forms For each field in the form that we are interested in <jsp:setproperty name="beannameinpage" property="propname" /> Get the values like this <jsp:getproperty name="beannameinpage" property="propname" />

14 JSP and Java classes (3) Any bean that we have with <jsp:usebean> we can use just like any other class Having it as a bean just lets us use it to get the submi\ed form values We can access public fields and func+ons of classes in javascript e.g. var thename = '${ccbean.getname()}'; NB: can t pass javascript variable to Java(???)

15 Managing client state (1) Client state is informa+on that is specific to a par+cular use- session of the applica+on i.e., not applica+on- wide informa+on That we can handle, e.g. in sta+c fields, database, etc.

16 Managing client state (2) h\p:// h\p:// Tutorial/Servlet- Tutorial- Session- Tracking.html We can use sessions to help us manage the client state for us Uses cookies by default. Supposed to work even if cookies are disabled, but... On one page: <%... session.seta\ribute(aername, aerval)... %> On another page: <%.. session.geta\ribute(a\rname)... %>

17 Managing client state (3) Special func+ons available in session: getid() isnew() getcrea+ontime() Just a number use it with Date getlastaccessedtime() How long is the session valid? getmaxinac+veinterval() setmaxinac+veinterval()

18 Deploying the JSP files (1) You will create a WAR file similar to a jar file, but for web applica+ons You can use jar to examine and change a WAR file You need to specify the Context Path, which is the directory where the app is located In Netbeans, you can do it in Project Proper+es Run More generally, it is in the context.xml file, which gets put into the META- INF directory (same directory as the manifest) in the WAR file

19 Deploying the JSP files (2) Then upload to an appropriate server There are commercial services that provide web servers e.g. h\ps:// has plans that should be free for low usage (CuC has not tried it) For a Tomcat server/container, you would look for the manager page.

20 Web services Idea: server provides some computa+on which is returned to the client Desktop applica+on Server applica+on Web browser (via a web page) Limita+on: the web service has to be on the same domain as the web page which calls it Some work- arounds, e.g. JSONP, CORS, etc. Ouen machine- oriented rather human- oriented i.e. returning XML, or JSON rather than HTML or text

21 JSON (1) Javascript Object Nota+on Originally from javascript, but now (also) a general data exchange format Replacing XML in some instances More compact h\p://json.org/ But, we cannot (yet) define the structure Cf. DTDs, Schema, etc. for XML Upcoming: h\p://json- schema.org/

22 JSON (2) 4 Kinds of informa+on: Objects, Arrays, Keys, Values Objects: {key1:value1, key2:value2...} Arrays: [value1, value2,...] Keys are strings Values can be objects, arrays, numbers, strings, true, false, null

23 JSON (3) {"np": {"tokens":[{"token": "an"}, {"token":"espresso" }], "count":3}} [{},true,null]

24 Constructors: JSON (3) h\p:// h\p:// JSONObject(java.u+l.Map map) JSONObject(java.lang.Object bean) JSONObject(java.lang.String JSONtextString) JSONArray(java.u+l.Collec+on collec+on) JSONArray(java.lang.Object array) JSONArray(java.lang.String JSONtextString)

25 JSON (4) Gezng info from a JSONObject Object get(string key) int getint(string key) boolean getboolean(string key)... JSONObject getjsonobject(string key) JSONArray getjsonarray(string key) Iterator keys() int length() //number of keys

26 JSON (5) Gezng info from a JSONArray Object get(int index) int getint(int index) boolean getboolean(int index)... JSONObject getjsonobject(int index) JSONArray getjsonarray(int index) int length() //number of elements String join(string separator)

27 REST- ful Web Services There are a variety of techniques (e.g. SOAP, XML- RPC), but REST (aka REST- ful) is most common now REST = Representa+onal State Transfer Key ideas: everything (including queries) becomes a "resource" with a URL use HTTP opera+ons to provide database- like opera+ons over the internet

28 REST: HTTP and DB opera+ons DB CREATE RETRIEVE UPDATE DELETE HTTP PUT GET POST DELETE Not a perfect correspondance, since POST is also used when we have a large amount of data GET is ouen limited to ~2K characters Ideal: GET (and POST used for RETRIEVE) should not change the state of the server applica+on

29 How to make REST web services Can use any programming language We ll use Java s Jersey

30 REST service with Jersey (1) h\p://docs.oracle.com/javaee/6/tutorial/doc/gilik.html h\p://vichargrave.com/res~ul- web- service- development- with- netbeans- and- tomcat- tutorial/ h\p://

31 REST service with Jersey (2) Use an IDE! In Netbeans, when making a new project Java Web - > Web Applica+on (same as for JSP) New (same menu as for new Class) - > RESTful Web Services from Pa\erns - > Simple Root Resource - > Path = the path under the main applica+on directory The Context Path, same as with JSP - > Class name (the java class) - > Use Jersey specific features

32 Making web service handlers (1) Handler: the java code that is called when we do GET, POST, etc. Key idea: we use annota0ons to indicate the role that different pieces of the code play in the web service Always preceded Immediately precede the relevant code

33 Basic annota+ons What rela+ve path on the server will call this func+onality Rela+ve to Context Path AND then servlet mapping Specified in WEB- INF/web.xml e.g. <url- pa\ern>/webresources/*</url- pa\ern> => at the class gives the base for the methods /service at method gives the end point for the URL text ) (with previous class- => h\p:/host/contextpath/webresources/service/text

34 Basic The type of h\p request that the method The MIME type of the input data Use the constants: Mediatype.XXXXXX e.g. for (can also be MediaType.TEXT_PLAIN if no parameters) Op+onal for GET Omit if there is no data

35 Basic annota+ons The MIME type of the response, + "; charset=utf- (for GET) The following argument gets its value from the named query param e.g. myfunc+on(@queryparam( name ) String who) {} h\p://../?...name=somename the variable who is assigned SomeName You may need to call URLDecode.decode(who, UTF- 8 )

36 Basic annota+ons UriInfo var (for GET) All the query paramaters together in var, e.g. UriInfo ui) { Mul+valuedMap<String, String> queryparams = ui.getqueryparameters(); } String who = queryparams.getfirst( name"); h\p://../?...name=somename the variable who is assigned SomeName You may need to call URLDecode.decode(who, UTF- 8 )

37 Basic annota+ons (for POST, when form- encoded) The following argument gets its value from the named query param e.g. name ) String who) {} POSTed with name=somename the variable who is assigned SomeName You may need to call URLDecode.decode(who, UTF- 8 ) There are other annota+ons, more details

38 Managing client state REST- ful web services themselves do not (typically) handle client state But we can use JSP and sessions Or manually do cookies, etc

39 Deploying the web services Use a WAR file, as with JSPs

40 How to make a REST client How do we use REST- ful web services? Simplest is just load the URL May or may not be useful Can call web services from a web page On the same site Or using JSONP, CORS, etc, depending on service and server configura+on Can call web services from applica+ons Desktop OR server

41 Observa+on JSP- sites tend to have mul+ple pages The Java expressions are evaluated just once when the page loads Web service based sites tend to update the informa+on on a page more ouen than going to a separate page Web services can be called without (re)loading a page

42 Calling a web service from page (1) Web services are called using Javascript Idea: Use XMLH\pRequest Can do directly, but There are many libraries which make it easier e.g. jquery: h\p://jquery.com

43 Calling a web service from page (2) jquery.get(url, handleresult); jquery.post(url, params, handleresult); Parameters: For GET, the url will contain any paramaters: p1=v1&p2=v2 For POST, the paramters are passed to jquery

44 Calling a web service from page (3) jquery.get(url, handleresult); jquery.post(url, params, handleresult); handleresult is (the name of) a func+on you write (it can be called anything) that will be called when the web service is done. It has 3 arguments: func+on handleresult(data, status, jqxhr) {} data: the data that is returned (may be an Object) status: h\p status, e.g. success jqxhr: jquery object with the results, especially jqxhr. responsetext

45 Calling a web service from Java (1) Simplest way: Use H\pURLConnec+on from URL See WeblichtClient But there are also libraries to help

46 Calling a web service from Java (2) h\ps://blogs.oracle.com/enterprisetech+ps/entry/consuming_res~ul_web_services_with The Jersey way WeblichtClientJersey (web client, POST) FAAGET (desktop app, GET)

47 Calling a web service from Java (3) What we need: Jersey Client This calls the web service Client myclient = Client.create(); Jersey WebResource(s) These are descrip+ons of the web services we ll call WebResource someresource = myclient.resource(urlforwebservice); ClientResponse This has the informa+on that is returned from the web service (and the h\p informa+on)

48 Calling a web service from Java (4) ClientResponse: GET Mul+valuedMap queryparams = new Mul+valuedMapImpl(); queryparams.add( param", value"); ClientResponse response = mywebresource.queryparams (queryparams).get(clientresponse.class); Other op+ons possible, e.g..type() for the return MIME type

49 Calling a web service from Java (5) ClientResponse: POST ClientResponse response = mywebresource.type(...").post(clientresponse.class, input); Notes: If we have parameters, we use Mul+valuedMap, as with GET Type: MediaType.APPLICATION_FORM_URLENCODED_TYPE Input: the Mul+valuedMap object If we do not have parameters (e.g. as in Weblicht services) Type: whatever is appropriate (e.g. tcf+xml ) Input: the data to be processed

50 Calling a web service from Java (6) Dealing with the response int status = response.getstatus(); 200 is OK, 404 is not found, etc. Type result = response.geten+ty(type.class); e.g. String results = response.geten+ty(string.class) JSONObject jsresults = response.geten+ty(jsonobject.class)