Web addon
Introduction
zkdb - ZK Data binding tool
Developers guide
Developers guide
Creating a user interface data model
There are three alternative ways to implement user interface data model. The first one is to retrieve information from an XML file. Its use is simple and easy to implement during user interface prototyping phase.
A second alternative is to create a set of glue classes, similar to a DAO object, that are responsible for retrieving user interface data from the storage system, and save changes back.
Finally, there is a way to get this glue layer in a declarative way, by means of an XML behavior descriptor.
As an example, a let's build a web page for querying countries and cities, the data will be modeled by the following XML model:
After creating the data model, you can make use of it from any zul page including a xmlDataSource component:
Binding data model simple values to zk components
In the previous section, we saw how to declare a sample data model. To bind a component to a data model element, the bind attribute can be used. The bind attribute value must be composed of the data source path to be used, a colon separator, and the xPath element to the data model element.
The data source is selected based on the zk path. Both simple paths (/model1) or full paths (//page1/window1/window2/model2).
The data model element is specified using its XPath. Internally, it's using an Apache commons JXPath version.
So, in order to display a label with the value of the "name" attribute of the XML document "title" entity, set the bind attribute of a new label the value "/mydata:/title/@name", as shown in the following example:
Mind that this binding is only one way, because the label object does not allow the user to change its content. When using a textbox, checkbox or any other input element, the binding will be bidirectional, allowing the user to change the associated DOM XML file. Anyway, the changes will not be serialized to the original XML file.Binding data model context
To easiest the readability and maintainability of the code, and to shorten in XPath paths, some components can works as a relative xpath context for the contained ZK components. When a container type object is associated with a data model element, binds on child components that do not specify a data source are understood as parent container relative XPaths.
The components that can act as context data model implement the es.caib.zkib.BindContext interface. Currently, grid, lisbox, row and form components. Due to implementation constraints, the listiem object does not implement the aforementioned interface.
The simplest of those components is the Form object (which derives from Vbox). For context associations, the attribute to be used is called datapath, as shown in the following example:
In this example, both the object label, as the textbox object refer to the same attribute @name, which is relative to the context /mydate:/title. When the user changes the textboxitem, the same text will be shown on the label. Mind the synchronization will only be done when the data is sent to the server, by means of any ZK event. In order to make user interface to be more responsive, simply add an onChange or onChanging null handler to the textbox component.
Binding Data Model Collections
Components of type listbox and grid behave as complex containers of object collections. These components can be assigned a Xpath expression that does not identify a single object, but a collection of objects or values. In this case, the system will generate a row for each of the values retrieved by the XPath query.
In order to define how to render listbox elements (listiem) bound to each data model row, the dataitem component should be used. The dataitem component is used as a template for the generation of any listitems. It should be noted that the each generated listitem is bound to a single object from the data model collection. This object is used also as a data context for the listcell's bound xPath. More and more, the attribute bind on the dataitem is the XPath that point to the value of the listitem.
In a similar way, in order to define how a grid row should be rendered, the datarow component should be used. It is used as a template for the actual rows generated. A row will be generated for each single element obtained from the data model collection. This object is bound to it's corresponding row and serves as the data context for the row children components.
So, the following example illustrates how to show the countries on a list component:
Note that the dataitem component has a dual behavior regarding the data model. On one side, it serves as a context to the inner object, and by the other side, it is assigned a value of the data model, according to the specification of the listitem component.Components as a data source
The listbox component has a dual role, as a data consumer and as a data source. We've seen how listbox component can act as a data consumer in the previous pages. No we'll see how is it acting as a data source.
Any zul component can use the listbox path as the left handside member of a bind expression. In such a case, the result would be the same than binding such components to the xpath relative to the listitem currently selected at the list box. When no listbox element is selected, the resulting XPath will be void, and thus the component will be disabled. When the selected listitem changes, automatically the listbox bound components will c
As an example, the following code will show the name of the selected country, allowing the user to modify it.
Additionally, you can display a grid with the names of the cities of the selected country. Using the previous listbox as the data source, the component synchronization is automatic:
Data model manipulation
The data model can be manipulated directly using the JXPathContext interface or indirectly through components, Whenever the user changes the contents of a ZK component, which is bound to a data model object, the change is propagated to the model, which in turn, propagates it to any ZK component that is bound to the modified data model object.
To ease data manipulation, the listbox object, has two new methods: addNew and delete. The first one creates a new object in the data model, and therefore in the listbox, while the second one removes it from the list and the model. Additionally, the autocommit attribute determines whether listbox will try to perform a commit the data model each time the user changes the selected item.
Alternatively, the data model can be directly manipulated through a Apache's commons-JXPath derived package. Every data source component (including datamodel and lisbox) contains a JXPathContext. Through this context JXPath invocations can be made, usign getValue, setValue, removePath or createPath methods. For more information about JXPath use, please review the available docs at: http://jakarta.apache.org/commons/jxpath/
Mind that the components will be notified of any change made through JXPath API, but the won't be noticed of any change made directly to the underlying data model. On the undesirable case underlying data objects are modified directly, you can force the components to be notified by getting a Pointer to the modified object and calling the invalidate method on it.
As an example, the following example shows how to delete a city or ad a new one to the data model:
row = self.parent;
ctx = row.dataSource.jXPathContext;
ctx.removePath(row.xPath);
ctx.getPointer("/").invalidate();
Building dynamic data model
While building the data model using XML files is possible, it's advisable to use more dynamic data models in the production environment. Alternatively, ZKIB module provides a set of classes that ease interaction with data models based on JDBC databases and object-oriented layers like Hibernate or EJB. Additionally.
To make use of these dynamic data models, the developer must implement one or more instances of the DataNode object. These DataNode objects act as wrapping around the actual business bean, managing the persistence layer. In general, you should define a class for each XML file equivalent entity. Thus, in the previous example, the developer should implement classes for the root (my-data), title, country and city objects. In some cases you won't need to develop a new DataNode class as long as the data object needs not to be persisted. For those simple data objects, a SimpleDataNode object can be used.
Each class is responsible for encapsulating a business object, and for its serialization to the persistent repository, usually a database. Also, each class is responsible for retrieving child objects. The children population function is performed by the finder interface.
A DataNode object must implement the following methods:
Method
Attributes
Description
DataContext
Optionally, you must declare the "finders", by calling the method addFinder
doInsert
Insert a new object in the persistent storage
doUpdate
Update an object in the storage persitente
doDelete
Update an object in the storage persitente
It's noticeable, that doInsert, doDelete and doUpdate methods are always invoked in a transactional context, coordinated through the commit method of the DataSource. The DataNode derived objects can access the data of the underlying business object by calling the inherited method getInstance.
The Finder interface must implement the following methods:
Method
Result
Description
find
java.util.Collection
Retrieves a collection of business objects that are descendants of the current object. Note that this method should not construct DataNode objects that will wrap the business object later.
newInstance
Object
Creates a new business object, filling the default value of its attributes, depending on the context in which they are creating.
Thus, to implement the same countries data model, equivalent to the former XML file you should define the following business classes:
Country business class
package com.soffid.sample;
public class Country {
private String name;
private String abbreviation;
public String getName () {return name;}
public void setName (String name) {this.name = name;}
getAbbreviation public String () {return abbreviation;}
public void setAbbreviation (String abbreviation) {
this.abbreviation = abbreviation;
}
}
City business class
package com.soffid.sample;
public class City {
private String name;
public String getName () {return name;}
public void setName (String name) {this.name = name;}
}
Title business class
package com.soffid.sample;
public class Title {
private String name;
public String getName () {return name;}
public void setName (String name) {this.name = name;}
}
Now that we have the needed business classes, the next step is to create the a class that manages the root of the data tree. This class derives from SimpleDataNode because they do not allow the execution of the methods doInsert, doUpdate or doDelete. In its constructor defines two Finders, responsible for retrieving the list of countries (through a existing countryDAO class) and title (with code):
package com.soffid.sample;
import java.util.Vector;
import es.caib.zkib.datamodel.*;
import es.caib.zkib.datasource.*;
public class RootNode extends SimpleDataNode {
public RootNode(DataContext ctx) {
super(ctx);
// Title
addFinder("title",
new Finder () {
public java.util.Collection find() throws Exception {
Title t = new Title ();
t.setName ( "World countries" );
Vector v = new Vector();
v.add (t);
return v;
};
public Object newInstance() throws Exception {
throw new UnsupportedOperationException();
}
},
SimpleDataNode.class);
// Countries
addFinder("country",
new Finder () {
public java.util.Collection find() throws Exception {
return CountryDAO.findAll ();
};
public Object newInstance() throws Exception {
throw new UnsupportedOperationException();
}
},
CountryNode.class);
}
}
The CountryNode object class referenced in the previous class will wrap for Country objects got by DAO. This class is responsible to retrieve and instantiate City objects from the Country. It is derived from SimpleDataNode because no update, insert or delete of countries is allowed:
package com.soffid.sample;
import java.util.Vector;
import es.caib.zkib.datamodel.*;
import es.caib.zkib.datasource.*;
public class CountryNode extends DataNode {
public CountryNode(DataContext ctx) {
super(ctx);
addFinder("city",
new Finder () {
public java.util.Collection find() throws Exception {
Country c = (Country) getInstance();
return CityDAO.findByCountry (c.abbreviation);
};
public Object newInstance() throws Exception {
Country country = (Country) getInstance();
City city = new City();
city.setCountryAbbreviation (country.getAbbreviation());
return city;
}
},
CityNode.class);
}
}
Finally, the CityNode class is responsible for managing City persistent objects. In this case there is no finder instance because the City has no children available:
package com.soffid.sample;
import java.util.Vector;
import es.caib.zkib.datamodel.*;
import es.caib.zkib.datasource.*;
public class CountryNode extends DataNode {
public CountryNode(DataContext ctx) {
super(ctx);
}
protected void doInsert() throws Exception {
CityDAO.insert ((City) getInstance());
}
protected void doUpdate() throws Exception {
CityDAO.update ((City) getInstance());
}
protected void doDelete() throws Exception {
CityDAO.delete ((City) getInstance());
}
}
In summary, we have had to generate four kinds of objects corresponding to the three types of element of the XML document:
my-data: RootNode class derived from SimpleDataNode . It contains two finders, one for title, and one for country.
title: is using SimpleDataNode class.
country: CountryNode class derived from SimpleDataNode. It contains a finder that allows the instantiation of City objects.
city: CityNode class derived from DataNode. Implements methods to persist City object. It has no finder.
Definition of dynamic models using XML descriptors
Definition of dynamic models using XML descriptors
Introduction
It is possible to define the underlying data model without having to write java code. To do this, you must use an XML descriptor which describes the DataNodes and their relationships. An skeleton XML descriptor has the following structure:
...
...
...
Within the XML tag whose root is always zk-ib, you can specify one or more DataNodes. Each DataNode has a unique name. Within each DataNode, you can define multiple finders. Each finder specifies a name and a type. The name will be used to build xpaths, whlie the type identifies the type of DataNode this xpaths refers to.
Within each finder you can define multiple search handlers. They will be responsible for retrieving data from persistent storage, just like the find method on the finder interface. Additionally, you can define one or new instance handlers. They will be responsible for creating new business objects on user request.
Finally, each DataNode can have many persistence handlers. They will act just lik the doInsert, doUpdate and doDelete methods on DataNode class. Each type of handler can be executed conditionally, depending on expressions to be evaluated at run time. These expressions can use the following predefined variables:
Additionally, EL expressions may refer to all variables defined within the DataSource. Those variables are accessed via JXPathContext.getVariables() method. To use of this type of data models, simply create a datamodel component on the ZUL page and assign the src attribute the path to the XML descriptor. The path can be a web component or a class path resource.
Variable
Value
self
Current DataNode
instance
Business object wrapped into current DataNode
parent
Parent DataNode
parent.instance
Business object wrapped into parent DataNode
datasource
DataSoruce the current DataNode belongs to
Ejb-handler Handler
It is responsible for persisting the object via a stateless session bean. The following attributes are supported:
Attribute
Usage
jndi
JNDI path to EJB Home interface
if
EL expression that must be evaluated to true prior to handler action
unless
EL expression that must be evaluated to false prior to handler action
Inside the handler, you should specify the suitable insert-method, delete-method and update-method tags. There is a mandatory attribute named method. This attribute must contain the name of the method to invoke. Additionally, the parameters to use can be specified. The following example shows an ejb-handler that uses an EJB whose only parameter is the data object:
...
This second example shows how to call a method with slightly complex parameters:
Script-handler Handler
It ca be used to persist the business objects using BSH scripts. Supports the following attributes:
Attribute
Usage
if
EL expression that must be evaluated to true prior to handler action
unless
EL expression that must be evaluated to false prior to handler action
Inside the handler, you can use the insert-script, delete-script and update-script tags. Each contains the BSH script that the engine will execute to perform inserts, deletes or updates. Within the BSH script you can refer to the same EL expressions predefined variables:
Variable
Value
self
Current DataNode
instance
Business object wrapped into current DataNode
parent
Parent DataNode
parent.instance
Business object wrapped into parent DataNode
datasource
DataSoruce the current DataNode belongs to
The following example shows how to save objects in file Country:
import java.io.*;
f = new FileOutputStream ("country."+instance.abbreviation);
oos = new ObjectOutputStream (f);
oos.writeObject (instance);
oos.close ();
f.close ();
import java.io.*;
f = new FileOutputStream ("country."+instance.abbreviation);
oos = new ObjectOutputStream (f);
oos.writeObject (instance);
oos.close ();
f.close ();
import java.io.*;
f = new File ("country."+instance.abbreviation);
f.delete ();
...
Collection-handler Handler
This handler is applicable when the persistence of this object is managed by the parent dataNode. The allowed attributes are:
Attribute
Usage
collection
EL expression that identifies the collection onto which the business object must be added or removed
if
EL expression that must be evaluated to true prior to handler action
unless
EL expression that must be evaluated to false prior to handler action
The following example shows how you could manage objects City as a collection of objects within the object Country, which in turn is saved on a disk arhivo:
Custom-handler Handler
The custom-handler provides coverage for situations where you need a more sophisticated handler and it is not worth to use a bsh script., In this case the persistence must be done be a java class that implements the PersistenceHandler interface, and the custom-handler specifying the name of the class used. The attributes are:
Attribute
Usage
className
Name of the java class to be used
if
EL expression that must be evaluated to true prior to handler action
unless
EL expression that must be evaluated to false prior to handler action
Data validation
The validation tag is responsible for performing basic checks regarding mandatory attributes and valid attribute values before being submitted to the persistence handler. The validation tag may contain one or more attribute-validation and script-validation tags. The verification will be performed before running the insert or update handler.
attribute-validator contains the following attributes:
Attribute
Usage
expr
EL expression pointing to the attribute to validate
friendlyName
Text to be presented to the user on validation failure. If there is a ZK label with this text, it will be localized based on current user language preference.
notNull
true is the attribute is mandatory
maxLength
Maximum length of the attribute
minValue
Minimum value in case of numeric attributes
maxValue
Maximum value in case of numeric attributes
attribute-script contains a script that will be executed to validate the business object.
Example:
if (instance.abbreviaton.equals(“CT”))
{
throw new RuntimeException (“Catalonia is not a country yet”);
}
...
EJB find handler: ejb-finder
Handles the method to retrieve business objects via a stateless session bean. Supports the following attributes:
Attribute
Usage
jndi
JNDI path to EJB Home interface
method
EJB Bean method to get business objects
if
EL expression that must be evaluated to true prior to handler action
unless
EL expression that must be evaluated to false prior to handler action
Additionally, it can specify one or more parameters in a way similar to the ejb-handler methods
ejb-finder example
...
...
script-finder handler
It is responsible for retrieve business objects from the persistence layer using BSH scripts. The following attributes are supported
Attribute
Usage
if
EL expression that must be evaluated to true prior to handler action
unless
EL expression that must be evaluated to false prior to handler action
The contained bsh script must return a collection of business objects. If the returned object is not a collection object, the engine will treat the returned object as a singleton.
In the following example, the script finder retrives all countries saved to disk in the previous example:
...
import java.io.*;
files[] = new File(".").listFiles ( new FilenameFilter () {
public boolean accept (File dir, String name) {
return name.startsWith("coutnry.");
}
);
v = new java.util.Vector();
for (int i = 0; i < files.length; i++)
{
f = new FileInputStream (files[i]);
ois = new ObjectInputStream (f);
v.add (ois.readObject ();
ois.close ();
f.close();
}
return v;
...
collection-finder handler
Similar to collection-handler, this handler retrieves the list objects contained on a parent collection.
Attribute
Usage
collection
EL expression that contains the objects collection
if
EL expression that must be evaluated to true prior to handler action
unless
EL expression that must be evaluated to false prior to handler action
The following example shows how you could retrieve City objects as a collection of objects within the County object:
...
...
custom-finder handler
The custom-finder provides coverage for situations where you need a more sophisticated handler and is not worth implement it using a script. In this case a class that implements the FinderHandler interface must be developed, and the custom-finder specifying the name of the class must be used
Attribute
Usage
className
Name of the FinderHandler class
if
EL expression that must be evaluated to true prior to handler action
unless
EL expression that must be evaluated to false prior to handler action
new-instance-script handler
It is responsible for instantiating new objectswithin a finder on user request .
Attribute
Usage
if
EL expression that must be evaluated to true prior to handler action
unless
EL expression that must be evaluated to false prior to handler action
With the following example the model will alow to create a new city within a country:
...
c = new City();
c.countryAbbreviation = instance.abbreviation;
return c;
...
new-instance-bean handler
This handler allows the craetion of a new business object and assign default attribute values. The value of the bean attributes is specified using multiple instances of the bean-attribute tag
Attribute
Usage
className
Name of the business object class
if
EL expression that must be evaluated to true prior to handler action
unless
EL expression that must be evaluated to false prior to handler action
bean-attribute/name
Name of the attribute
bean-attribute/value
EL expression with the value to assign
With the following example would create a new city within a country:
...
...
custom-attribute handler
Generates virtual attributes derived from other attributes or external elements of the application. It can be applied to any DataNode to add attributes that were not originally present at the underlying business object. Those attributes will be presented at the JXPath interface just as if they were business objects attributes
Attribute
Usage
name
Name of the virtual attribute
expr
EL expression that evaluates de attribute value
if
EL expression that must be evaluated to true prior to handler action
unless
EL expression that must be evaluated to false prior to handler action
depends
XPath to a attribute or business object the expression depends on
It's important to properly set the depends attribute as long as the attribute will be reevaluated whenever a dependent attribute has been changed.
The custom attribute can have an empty EL expressions and use a BeanShell script instead. Here is an example of both aproaches:
@network@mask
return instance.network + “/” + instance.mask;
...
Using dynamic models
To use dynamic models XmlDataSource tag must be replaced by datamodel. The datamodel tag has the following attributes:
Attribute
Usage
id
ZK Identifier
className
root DataNode class name
src
XML resource name for XML dynamic data model
rootNode
Root node type for dynamic data model
className usage is not compatible with src and rootNode attributes.
rootNode attribute is mandatory when using XML dynamic data models.