Maven & xjc

Maven integration of xjc is available from a number of sources.  In this post I'll look at some examples of what is available from jvnet.

Documentation is available here: http://confluence.highsource.org/display/J2B/JAXB2+Basics+Plugins

Simple Example

    <plugin>
        <groupId>org.jvnet.jaxb2.maven2</groupId>
        <artifactId>maven-jaxb2-plugin</artifactId>
        <executions>
            <execution>    
                <goals>
                    <goal>generate</goal>
                </goals>
            </execution>
        </executions>
        <configuration>
            <extension>true</extension>
           <schemaDirectory>src/main/resources</schemaDirectory>
           <schemaIncludes>
               <include>my_schema.xsd</include>
           </schemaIncludes>
            <generateDirectory>src/main/java</generateDirectory>
            <generatePackage>com.me.generated</generatePackage>
            <episode>false</episode>     
        </configuration>
    </plugin>

This simple example generates my_schema.xsd JAXB classes and puts them into src/main/java in the com.me.generated package.  This is pretty much the most simple example of this plugin.

Example With Catalogue File

    <plugin>
        <groupId>org.jvnet.jaxb2.maven2</groupId>
        <artifactId>maven-jaxb2-plugin</artifactId>
        <version>0.8.2</version>
        <executions>
            <execution>
                <goals>
                    <goal>generate</goal>
                </goals>
            </execution>
        </executions>
        <configuration>
            <extension>true</extension>
            <generateDirectory>src/main/java</generateDirectory>

            <catalogs>
                <catalog>
                    <dependencyResource>            
                        <groupId>com.me.common</groupId>
                        <artifactId>xsd-project</artifactId>
                        <resource>common.catalog</resource>
                    </dependencyResource>
                </catalog>
            </catalogs>

            <episodes>
                <episode>
                    <groupId>com.me.common</groupId>
                    <artifactId>xsd-project</artifactId>
                </episode>
            </episodes>    

            <episode>true</episode> 

            <args>
                <arg>-XtoString</arg>
                <arg>-Xequals</arg>
                <arg>-XhashCode</arg>
            </args>
            <plugins>
                <plugin>
                    <groupId>org.jvnet.jaxb2_commons</groupId>
                    <artifactId>jaxb2-basics</artifactId>
                    <version>0.6.4</version>
                </plugin>
             </plugins>      
        </configuration>    
    </plugin>


This plugin will parse the available *.xsd files in the src/main/resources directory and create JAXB annotated classes in the src/main/java directory.  If an bindings.xjb is also present in the resources directory then this will be used.

generateDirectory - where to put the JAXB classes.
catalogs - These allow an xsd reference to be overridden and redirected locally or into a jar file.
episodes - This tells xjc to not create code for these xsd because it is already available.
episode - This tells xjc to generate an episode file for these xsds
args - optional arguments to add to the JAXB classes.  This requires the plugin that follows it.

Catalog File

A catalog file allows the xsd schema locations to be altered and redirected.  If a schema file has an import such as


    <xs:import namespace="http://www.me.com/common/config" />


Note there is no schemaLocation value.  This will fail the schema validation without a catalog file helping to tell xjc where the actual xsd source is.  A valid catalog file to do this would be

    PUBLIC "http://www.me.com/common/config" "maven:com.me.common:xsd-project!/config.xsd"

Here the first part of the catalog has the same namespace as the import namespace.  This is how they match. The second element can be a standard file location or, like here, a reference to an xsd in a jar which is a maven dependency.  It is only with the maven plugin that this maven:... reference will work.  Standard xjc does not recognise this notation. NOTE: there is a colon separating 'maven' from the groupId from the artifactId.  Putting a . instead will cause the catalogue redirect to not work and that can eat up time trying to find the reason why!!

Episode File

An episode file is just a standard bindings file.  It tells xjc not to create JAXB annotated classes for objects which may appear in an xsd (Not all the elements of the xsd need to be contained in an episode file although this would be a little unusual and require manually changing the episode file after generation).
This maven plugin can use episode files from other jars but can also be told to generate one using the

            <episode>true</episode> 

Common Errors

If you get a stack trace like this,

    com.sun.istack.SAXParseException2: SCD "x-schema::tns" didnt match any schema component

Then a schema is included in the episode file but never referenced.  If you can remove the episode file from the configuration then this will cure it.  Otherwise just create an empty schema which imports all the episode elements but does nothing with them.  I think this error is trying to be helpful and tell you when something is included and it doesn't need to be but the message isn't particularly clear.  Hopefully there may be an option to ignore this error in the future because an episode file may contain multiple schemas when you don't necessarily need them all.

XML Schemas / XSD

Here are a few simple memory joggers for how to create xml schema (xsd) files.

Namespaces

Namespaces are important parts of xsds.  They control the prefixes and help to remove ambiguity if there are two types which have the same name.  They are also import if you want to using binding files to create java classes in different packages for different files.

Normally a targetNamespace is defined for a schema along with a xmlns command which refers to the same targetNamespace.  The targetNamespace says that this xsd defines this namespace.  The xmlns is the same for all items but because it is the same as the targetNamespace it is satisfied by this file (it refers to itself so no import is needed).  The targetNamespace doesn't have to be included but makes it harder to extend or split up the schema later.


  <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" 
      xmlns:conf="http://www.mycompany.com/myapp/config" targetNamespace="http://www.mycompany.com/myapp/config">


Note that the conf and targetNamespace are the same.

ComplexType

ComplexType is very common.  It defines a link between one object that can have multiple children.  An example of a ComplexType is

    <xs:complexType name="person">
        <xs:annotation>
            <xs:documentation>
                The details about a person.
            </xs:documentation>
        </xs:annotation>
        <xs:sequence>
            <xs:element name="FirstName" type="xs:string" minOccurs="1" maxOccurs="1" />
            <xs:element name="Surname" type="xs:string" minOccurs="1" maxOccurs="1" />
            <xs:element name="Age" type="xs:int" minOccurs="0" maxOccurs="1" />
        </xs:sequence>
    </xs:complexType>


The complexType can then be referenced in another object

    <xs:element name="staff" type="person" minOccurs="0" maxOccurs="unbounded" />

and in xml the person would look like

    <Person>
        <FirstName>Fred</FirstName>
        <Surname>Bloggs</Surname>
        <Age>43</Age>
    </Person>

Enumeration

If an enumeration is being used the don't make it an anonymous one.  If this happens then the xjc parser cannot turn it into a Java enumeration but instead does some horrible string effort.  Therefore, always make enumerations proper types.


    <xs:simpleType name="YesNo">
        <xs:annotation>
            <xs:documentation>Yes or No enumeration</xs:documentation>
        </xs:annotation>
        <xs:restriction base="xs:string">
            <xs:enumeration value="YES" />
            <xs:enumeration value="NO" />
        </xs:restriction>
    </xs:simpleType>


Restrictions need to have a 'base' that is the type of all the enumerations that it includes.

Extension

One object can extend another to include extra values.  For example, the person complexType defined about in the person object can be extended,

    <xs:complexType name="ExtendedPerson" >

        <xs:annotation>

            <xs:documentation>More people details</xs:documentation>

        </xs:annotation>

        <xs:complexContent>

            <xs:extension base="person">

                <xs:sequence>

                    <xs:element name="Salutation" type="SalutationType" minOccurs="1" maxOccurs="1" />

                </xs:sequence>

            </xs:extension>

        </xs:complexContent>

    </xs:complexType>

Where SalutationType is another enumeration.  Once Java classes have been generated the ExtendedPerson class extends the Person class with salutationType being the only local variable.  So in xml

    <ExtendedPerson>
        <FirstName>Fred</FirstName>
        <Surname>Bloggs</Surname>
        <Age>43</Age>
        <SalutationType>MR</SalutationType>
    </ExtendedPerson>

Import

Sometimes it is useful to have an import from one schema into another.  This allows types to be used from different schemas.  Firstly include the xmlns for the right target into the schema header as follows,

    xmlns:com="http://www.mycompany.com/myapp/common" 

Then import a schemaLocation which tallies up to this namespace.  The import command is,

    <xs:import namespace="http://www.mycompany.com/myapp/common" schemaLocation="common.xsd"/>


Here the common.xsd must have a targetNamespace as the same as the namespace in the import statement, in this case 'http://www.mycompany.com/myapp/common'.

Binding Files

Binding files (.xjb) can be used to simplify the xjc command and create java objects in different target packages.  To use a binding file the different xsds must have different namespaces.  A binding file which allows different packages to be used could be,

    <jxb:bindings xmlns:jxb="http://java.sun.com/xml/ns/jaxb" version="2.0" xmlns:xsd="http://www.w3.org/2001/XMLSchema" >

        <jxb:bindings namespace="http://www.mycompany.com/myapp/common" schemaLocation="common.xsd" >

            <jxb:schemaBindings>

                <jxb:package name="com.mycompany.myapp.common"/>

            </jxb:schemaBindings>

        </jxb:bindings>

    

        <jxb:bindings namespace="http://www.mycompany.com/myapp/config" schemaLocation="config.xsd" >

            <jxb:schemaBindings>

                <jxb:package name="com.mycompany.myapp.config"/>

            </jxb:schemaBindings>

        </jxb:bindings>

    </jxb:bindings>

The binding file can be referenced using the -b command in xjc.

GlobalBindings

It is possible to have a bespoke element that needs to be parsed in a particular way.  This can be done with a globalBinding such as,

    <jxb:globalBindings fixedAttributeAsConstantProperty="true">
        <jxb:javaType name="com.my.SpecialElement" xmlType="my:specialElement"
                      parseMethod="com.my.SpecialElementAdaptor.unmarshal"
                      printMethod="com.my.SpecialElementAdaptor.marshal">
        </jxb:javaType>
    </jxb:globalBindings>

This can also be used to format standard types such as dates, although this will be global across all the schemas and will result in xjc creating Adaptors in weird packages!

    <jxb:globalBindings fixedAttributeAsConstantProperty="true">
        <jxb:javaType name="java.util.Date" xmlType="xs:dateTime"
                      parseMethod="com.my.DateTimeAdaptor.unmarshal"
                      printMethod="com.my.DateTimeAdaptor.marshal">
        </jxb:javaType>
    </jxb:globalBindings>

SchemaBindings

In the situation where there are multiple schemas in a binding file this globalBinding is unlikely to be good enough (or even work at all).  Therefore, the binding can also be included in the schema part so that the binding only applies to one schema.

    <jxb:bindings namespace="http://www.my.com/common" schemaLocation="common.xsd" >
        <jxb:schemaBindings>
            <jxb:package name="com.my.common.generated"/>
        </jxb:schemaBindings>
        <jxb:bindings node="//xs:simpleType[@name='DeletionDateTime']">  
            <jxb:javaType name="java.util.Date"
  parseMethod="com.my.DateTimeAdaptor.unmarshal"
  printMethod="com.my.DateTimeAdaptor.marshal"/>  
        </jxb:bindings>
    </jxb:bindings>

This form uses an xPath to find the correct simpleType.

    node="//xs:simpleType[@name='DeletionDateTime']"

Note that // means search everywhere in the document for a xs:simpleType with name 'DeletionDateTime'.

Both the GlobalBindings and the SchemaBindings create Adaptors which are just named Adaptor#.  This can cause name clashes when you have a hierarchy of projects (jars) which means that you can end up not using the correct adaptor.

XJC Extension & Adaptors

A further option to allow a specific adaptor to be used is to specify the adaptor that you want to use.  This can be done using the xjc extension.  Firstly you need to include the namespace in the bindings file.
    <jxb:bindings  version="2.1" xmlns:jxb="http://java.sun.com/xml/ns/jaxb" 
        xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:xjc="http://java.sun.com/xml/ns/jaxb/xjc">

Next you can then use the xjc options.

    <jxb:bindings namespace="http://com.my/data" schemaLocation="my-data.xsd">
        <jxb:schemaBindings>
            <jxb:package name="com.my.data.generated" />
        </jxb:schemaBindings>
        
        <jxb:bindings node="//xs:complexType[@name='_Name_']/xs:sequence/xs:element[@name='_Date_']">
            <xjc:javaType name="org.joda.time.DateTime" adapter="com.my.data.util.JodaDateAdaptor" />    
        </jxb:bindings>
    </jxb:bindings>

xjc

xjc is bundled with java and is used to parse xsd and xjb files to create JAXB annotated java classes for a particular xml schema.  Example commands are

To parse a single file

    xjc -d myapp/java -p com.mycompany.myapp config.xsd

To parse multiple files

    xjc -d myapp/java -p com.mycompany.myapp *.xsd

To parse multiple files using a binding

    xjc -d myapp/java -b myapp.xjb *.xsd

-d = The route directory to create the classes in

-p = The package from the route directory

-b = refer to a binding file

Spring and JSON

The integration between Spring and JSON objects is very strong and can be incredibly useful from a client web app.

Spring Setup

Spring requires very little setup.  Provided the Jackson classes are on the classpath

    <dependency>
        <groupId>org.codehaus.jackson</groupId>
        <artifactId>jackson-mapper-asl</artifactId>
        <version>1.9.7</version>
        <scope>compile</scope>
    </dependency>

Then spring is basically ready to go!

Returning JSON

Returning JSON to the client is the easiest part. Just return a class or list of classes from the spring MVC controller method and it will be transformed into JSON automagically and be available to the client.  The key piece of magic here is the @ResponseBody tag which tells spring that the return value should make up the whole of the response body of the Http Response. Also the produces = .. value tells spring to use the Jackson processor because we can the application/json mime type as the output.

Here is an example


    @RequestMapping(value = "/gettopics", method = RequestMethod.GET, produces = "application/json")
    @ResponseBody
    public List<String> getTopics(final HttpServletRequest request)
    {
        final List<String> topics = new ArrayList<String>();
        topics.add("topic1");
        topics.add("topic2");

        return topics;
    }


Here the topics List object gets changed to a javascript list.  This can be processed on the client side by getting a result object

    for (var i=0; i<result.length; i++){
        alert(result[i]);
    }

And that is basically it.  Obviously your choice of javascript library to do the ajax request will have an impact here.  JQuery or Dojo would be the most common.

Accepting JSON

Accepting an json object into a Spring MVC method is a little more tricky.  Firstly you have to create an object to marshal into such as

    public class JsonExample {

        /** Value 1. */
        private final String value1;

        /** Value 2. */
        private final String value2;

        /**
         * Construct this object.  The benefit here is that this object is now immutable.

         */
        @JsonCreator
        public JsonExample(@JsonProperty("value1") final String value1,
                           @JsonProperty("value2") final String value2){
            this.value1 = value1;
            this.value2 = value2;
        }

        /**
         * Get the first value

         */

        public String getValue1(){

            return value1;

        }

    }

The annotations here tell Jackson how to marshal the JSON into this java object.  However, if you don't want an immutable object you just create getters and setters and you don't need any annotations at all! In the MVC controller method we simply have a @RequestBody rather than @ResponseBody this time and it all just works.


    @RequestMapping(value = "/settopics", method = RequestMethod.POST)
    @ResponseBody
    public void setTopics(final HttpServletRequest request, @RequestBody final JsonExample jsonExample)
    {
        ...
    }

Here the @ResponseBody seems like it should be surplus to requirements but the client doesn't like it if it isn't there.

In the web client a Javascript object is created

    var topics = {
        value1 : 'my topic',
        value2 : 'another topic'
    };

    var stringToSend = json.stringify(topics);

Again the choice of javascript library to make this call is down to the user but here the dojo/json module has been used.  The content headers need to be set on the post request


    Content-Type : 'application/json'

Posting a List of Objects

You would think that if you posted a list of object then you could just declare List<JsonExample> in the spring method but unfortunately this doesn't work.  Instead you have to declare an extension to the List object such as

    public class JsonExampleList extends ArrayList<JsonExample> {
        private static final long serialVersionUID = 3412220511906097746L;
    }

It doesn't require anything in it at all but helps Jackson sort out what you really mean and then the marshalling can continue.  Without doing this Jackson will convert to a LinkedHashMap of values and you can process this manually if you want to but the tip above will help Jackson sort it out.

Oracle Spatial

Here are a few reminders for how to do the Oracle Spatial stuff

Using a Spatial Column

To use a spatial column in a table you need to create spatial metadata and a spatial index.  In SQL Developer you can do this by right clicking on the table and choosing Spatial - Update Spatial Metadata and Spatial - Create Spatial Index.  At this point many standard tools will be able to query and display the geometry out of the box.

Tools

uDig
http://udig.refractions.net/
Displays a Oracle Spatial Geometry by just choosing the column.  It is based on the Eclipse RCP (Rich Client Platform)

Georaptor
http://sourceforge.net/projects/georaptor/
A useful plugin for SQL Developer which makes the creation of the index and metadata more simple.  It has a viewer which is available within SQL Developer.

Validating Geometry

To validate a geometry column in a table you can use

    select sdo_geom.validate_geometry(<column_name>, 0.05) from <table_name>

where 0.05 is a tolerance value.

Dojo DataGrid

Dojo has a number of table type tools that can be used.  TableContainer helps with a table layout (see http://dojotoolkit.org/reference-guide/dojox/layout/TableContainer.html) but to display a genuine table of data the DataGrid is excellent.

Links / Docs

ItemFileReadStore: http://dojotoolkit.org/reference-guide/dojo/data/ItemFileReadStore.html

ItemFileWriteStore: http://dojotoolkit.org/reference-guide/dojo/data/ItemFileWriteStore.html
DataGrid: http://dojotoolkit.org/reference-guide/dojox/grid/DataGrid.html

Require / Define

Functionality required for the DataGrid is available in the following modules.

    dojo/data/ItemFileWriteStore
    dojox/grid/DataGrid

are needed to be able to use the DataGrid.  (I have in the past had some problems with the order of the require / define and putting the DataGrid towards the end of the list seemed to cure this).

ItemFileWriteStore / ItemFileReadStore

Both of these object back the DataGrid amongst other things (Tree for example).  They are relatively easy to configure.  In the most basic form just create a JSON object of rows such as


    var hardwareList = [
        { name: 'PC',          partNo: 'PC1',     available: true,  cost: 250.00},
        { name: 'Netbook', partNo: 'N1233', available: false, cost: 150.00},
        { name: 'Tablet',     partNo: 'IP3',       available: false, cost: 550.00},
        { name: 'Phone',     partNo: 'SGS3',   available: true,  cost: 350.00}    ];

Next create a wrapper JSON object which includes the name of the identifier here it is the 'name' attribute in the JSON data but it could be any attribute. Finally create the store

    var data = {identifier: "name", items: hardwareList};
    var store = new dojo.data.ItemFileWriteStore({data: data});

DataGrid

Now that we have the data we can create the DataGrid. We need to create the layout for this grid to say which bits of data make up with columns etc


    var layout = [[
        {'name': 'Name',    'field': 'name',   'width': '100px'},
        {'name': 'Part No', 'field': 'partNo', 'width': '70px'},
        {'name': 'Cost',    'field': 'cost',   'width': '70px'}
    ]];


Here the 'name' is the column name, the 'field' is the data attribute and 'width' is the column width.  This layout can then be used in the construction of the DataGrid


    var grid = new dojox.grid.DataGrid({
                                    id: 'myDataGridId',
                                    store: store,
                                    structure: layout,
                                    onRowClick: function(e){
                                        var rowIndex = e.rowIndex;
                                        var available = grid.store.getValue(grid.getItem(rowIndex), 'available');
                                            if (available){
                                                ...
                                            }
                                    }
    });

    grid.placeAt("myDivToReplace");
    grid.startup();



Here the id is the name of the DataGrid object in the html dom.  The store is the data created earlier, and the layout is the column information above.  There are a number of event handlers which can be added and the onRowClick is shown here.  Within the onRowClick is the call

    grid.store.getValue(grid.getItem(rowIndex), 'available')

which shows how to get the correct data out of the store irrespective of the sorting that is going on.  If you just use the rowIndex on the hardwareList object then a sort on the column will give you the wrong result so this has to be used.  Finally set the grid locaion and call startup.

NOTE:  If the 'myDivToReplace' has no height then the DataGrid will have no height and not appear.  Set the height of the div you are replacing and the DataGrid will occupy that space.

Dojo Topic

Dojo provides a really useful topic based messaging system that can be used to send messages between decoupled pieces of javascript.

require / define

To use the topic functionality just include

    "dojo/topic"

at the top of the javascript file in the require or define section

Subscribe / Publish

It is really easy to use this functionality.  Firstly subscribe to a topic where the topic has a particular string name and a function to call as a result of a message,


    topic.subscribe("/log/add", function(message) {
        console.log(message);
    });


Now everytime a publish is done to the /log/add topic the function will be called.

To publish to that topic

    topic.publish("/log/add", "the message");

The publish subscribe isn't limited to one variable and can be passed multiple values.

That's really all there is to it.  The functionality is incredibly useful for larger web apps and particularly where the app code has been split into different modules and not all modules know about each other.  It helps to keep the hierarchy correct.

Dojo Mouse and Keyboard Events

Keyboard events in dojo are pretty easy for the most part!  You can just use the on() function to attach them and you are done! The on function is part of the "dojo/on" module which will need to be part of the require or define declaration.

Example to catch mouse down events on a particular dom


    on(registry.byId("myDiv"), 'mousedown', function(evt){
        console.log("Mouse Down Event");
    });


Catch keyup events on an input area.


    on(registry.byId("search"), "keyup", function(evt) {                
        doSearch(registry.byId("search").get('value'));
    });


The biggest problem arises when you want to catch a keyboard event on a dom object which doesn't normally accept keyboard input such as a div, span etc.  In this case you need to make it focusable and by far the easiest way to do that is to add a tabIndex.

    dom.byId("myDiv").tabIndex = 0; // Allow key events
    on(dom.byId("myDiv"), 'keypress', function(evt){
        console.log("KeyPress Event");
    });

You can use the dojo/keys module to check for the key value just like in Java Swing.


    if (evt.keyCode == dojo.keys.LEFT_ARROW){

    } else if (evt.keyCode == dojo.keys.RIGHT_ARROW) {

    }