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abstract public class: JXPathContext [javadoc | source]

Direct Known Subclasses:

JXPathContext provides APIs for the traversal of graphs of JavaBeans using the XPath syntax. Using JXPathContext, you can read and write properties of JavaBeans, arrays, collections and maps. JXPathContext uses JavaBeans introspection to enumerate and access JavaBeans properties.

JXPathContext allows alternative implementations. This is why instead of allocating JXPathContext directly, you should call a static newContext method. This method will utilize the JXPathContextFactory API to locate a suitable implementation of JXPath. Bundled with JXPath comes a default implementation called Reference Implementation.

JXPath Interprets XPath Syntax on Java Object Graphs

JXPath uses an intuitive interpretation of the xpath syntax in the context of Java object graphs. Here are some examples:

Example 1: JavaBean Property Access

JXPath can be used to access properties of a JavaBean.
public class Employee { public String getFirstName(){ ... } } Employee emp = new Employee(); ... JXPathContext context = JXPathContext.newContext(emp); String fName = (String)context.getValue("firstName");
In this example, we are using JXPath to access a property of the emp bean. In this simple case the invocation of JXPath is equivalent to invocation of getFirstName() on the bean.

Example 2: Nested Bean Property Access

JXPath can traverse object graphs:
public class Employee { public Address getHomeAddress(){ ... } } public class Address { public String getStreetNumber(){ ... } } Employee emp = new Employee(); ... JXPathContext context = JXPathContext.newContext(emp); String sNumber = (String)context.getValue("homeAddress/streetNumber");
In this case XPath is used to access a property of a nested bean.

A property identified by the xpath does not have to be a "leaf" property. For instance, we can extract the whole Address object in above example:

Address addr = (Address)context.getValue("homeAddress");

Example 3: Collection Subscripts

JXPath can extract elements from arrays and collections.
public class Integers { public int[] getNumbers(){ ... } } Integers ints = new Integers(); ... JXPathContext context = JXPathContext.newContext(ints); Integer thirdInt = (Integer)context.getValue("numbers[3]");
A collection can be an arbitrary array or an instance of java.util. Collection.

Note: in XPath the first element of a collection has index 1, not 0.

Example 4: Map Element Access

JXPath supports maps. To get a value use its key.
public class Employee { public Map getAddresses(){ return addressMap; } public void addAddress(String key, Address address){ addressMap.put(key, address); } ... } Employee emp = new Employee(); emp.addAddress("home", new Address(...)); emp.addAddress("office", new Address(...)); ... JXPathContext context = JXPathContext.newContext(emp); String homeZipCode = (String)context.getValue("addresses/home/zipCode");
Often you will need to use the alternative syntax for accessing Map elements:
String homeZipCode = (String) context.getValue("addresses[@name='home']/zipCode");
In this case, the key can be an expression, e.g. a variable.
Note: At this point JXPath only supports Maps that use strings for keys.
Note: JXPath supports the extended notion of Map: any object with dynamic properties can be handled by JXPath provided that its class is registered with the JXPathIntrospector .

Example 5: Retrieving Multiple Results

JXPath can retrieve multiple objects from a graph. Note that the method called in this case is not getValue, but iterate.
public class Author { public Book[] getBooks(){ ... } } Author auth = new Author(); ... JXPathContext context = JXPathContext.newContext(auth); Iterator threeBooks = context.iterate("books[position() < 4]");
This returns a list of at most three books from the array of all books written by the author.

Example 6: Setting Properties

JXPath can be used to modify property values.
public class Employee { public Address getAddress() { ... } public void setAddress(Address address) { ... } } Employee emp = new Employee(); Address addr = new Address(); ... JXPathContext context = JXPathContext.newContext(emp); context.setValue("address", addr); context.setValue("address/zipCode", "90190");

Example 7: Creating objects

JXPath can be used to create new objects. First, create a subclass of AbstractFactory and install it on the JXPathContext. Then call createPathAndSetValue() instead of "setValue". JXPathContext will invoke your AbstractFactory when it discovers that an intermediate node of the path is null. It will not override existing nodes.
public class AddressFactory extends AbstractFactory { public boolean createObject(JXPathContext context, Pointer pointer, Object parent, String name, int index){ if ((parent instanceof Employee) && name.equals("address"){ ((Employee)parent).setAddress(new Address()); return true; } return false; } } JXPathContext context = JXPathContext.newContext(emp); context.setFactory(new AddressFactory()); context.createPathAndSetValue("address/zipCode", "90190");

Example 8: Using Variables

JXPath supports the notion of variables. The XPath syntax for accessing variables is "$varName".
public class Author { public Book[] getBooks(){ ... } } Author auth = new Author(); ... JXPathContext context = JXPathContext.newContext(auth); context.getVariables().declareVariable("index", new Integer(2)); Book secondBook = (Book)context.getValue("books[$index]");
You can also set variables using JXPath:
context.setValue("$index", new Integer(3));
Note: you can only change the value of an existing variable this way, you cannot define a new variable.

When a variable contains a JavaBean or a collection, you can traverse the bean or collection as well:

... context.getVariables().declareVariable("book", myBook); String title = (String)context.getValue("$book/title); Book array[] = new Book[]{...}; context.getVariables().declareVariable("books", array); String title = (String)context.getValue("$books[2]/title);

Example 9: Using Nested Contexts

If you need to use the same set of variable while interpreting XPaths with different beans, it makes sense to put the variables in a separate context and specify that context as a parent context every time you allocate a new JXPathContext for a JavaBean.
JXPathContext varContext = JXPathContext.newContext(null); varContext.getVariables().declareVariable("title", "Java"); JXPathContext context = JXPathContext.newContext(varContext, auth); Iterator javaBooks = context.iterate("books[title = $title]");

Using Custom Variable Pools

By default, JXPathContext creates a HashMap of variables. However, you can substitute a custom implementation of the Variables interface to make JXPath work with an alternative source of variables. For example, you can define implementations of Variables that cover a servlet context, HTTP request or any similar structure.

Example 10: Using Standard Extension Functions

Using the standard extension functions, you can call methods on objects, static methods on classes and create objects using any constructor. The class names should be fully qualified.

Here's how you can create new objects:

Book book = (Book) context.getValue( "org.apache.commons.jxpath.example.Book.new ('John Updike')");
Here's how you can call static methods:
Book book = (Book) context.getValue( "org. apache.commons.jxpath.example.Book.getBestBook('John Updike')");
Here's how you can call regular methods:
String firstName = (String)context.getValue("getAuthorsFirstName($book)");
As you can see, the target of the method is specified as the first parameter of the function.

Example 11: Using Custom Extension Functions

Collections of custom extension functions can be implemented as Functions objects or as Java classes, whose methods become extenstion functions.

Let's say the following class implements various formatting operations:

public class Formats { public static String date(Date d, String pattern){ return new SimpleDateFormat(pattern).format(d); } ... }
We can register this class with a JXPathContext:
context.setFunctions(new ClassFunctions(Formats.class, "format")); ... context.getVariables().declareVariable("today", new Date()); String today = (String)context.getValue("format:date($today, 'MM/dd/yyyy')");
You can also register whole packages of Java classes using PackageFunctions.

Also, see FunctionLibrary , which is a class that allows you to register multiple sets of extension functions with the same JXPathContext.

Configuring JXPath

JXPath uses JavaBeans introspection to discover properties of JavaBeans. You can provide alternative property lists by supplying custom JXPathBeanInfo classes (see JXPathBeanInfo ).


See XPath Tutorial by W3Schools
. Also see XML Path Language (XPath) Version 1.0

You will also find more information and examples in JXPath User's Guide
Field Summary
protected  JXPathContext parentContext     
protected  Object contextBean     
protected  Variables vars     
protected  Functions functions     
protected  AbstractFactory factory     
protected  IdentityManager idManager     
protected  KeyManager keyManager     
protected  HashMap decimalFormats     
 protected JXPathContext(JXPathContext parentContext,
    Object contextBean) 
    This constructor should remain protected - it is to be overridden by subclasses, but never explicitly invoked by clients.
Method from org.apache.commons.jxpath.JXPathContext Summary:
compile,   compilePath,   createPath,   createPathAndSetValue,   getContextBean,   getContextPointer,   getDecimalFormatSymbols,   getFactory,   getFunctions,   getIdentityManager,   getKeyManager,   getLocale,   getNamespaceContextPointer,   getNamespaceURI,   getParentContext,   getPointer,   getPointerByID,   getPointerByKey,   getRelativeContext,   getValue,   getValue,   getVariables,   isLenient,   iterate,   iteratePointers,   newContext,   newContext,   registerNamespace,   removeAll,   removePath,   selectNodes,   selectSingleNode,   setDecimalFormatSymbols,   setFactory,   setFunctions,   setIdentityManager,   setKeyManager,   setLenient,   setLocale,   setNamespaceContextPointer,   setValue,   setVariables
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from org.apache.commons.jxpath.JXPathContext Detail:
 public static CompiledExpression compile(String xpath) 
    Compiles the supplied XPath and returns an internal representation of the path that can then be evaluated. Use CompiledExpressions when you need to evaluate the same expression multiple times and there is a convenient place to cache CompiledExpression between invocations.
 abstract protected CompiledExpression compilePath(String xpath)
    Overridden by each concrete implementation of JXPathContext to perform compilation. Is called by compile().
 abstract public Pointer createPath(String xpath)
    Creates missing elements of the path by invoking an AbstractFactory, which should first be installed on the context by calling "setFactory".

    Will throw an exception if the AbstractFactory fails to create an instance for a path element.

 abstract public Pointer createPathAndSetValue(String xpath,
    Object value)
    The same as setValue, except it creates intermediate elements of the path by invoking an AbstractFactory, which should first be installed on the context by calling "setFactory".

    Will throw an exception if one of the following conditions occurs:

    • Elements of the xpath aleady exist, but the path does not in fact describe an existing property
    • The AbstractFactory fails to create an instance for an intermediate element.
    • The property is not writable (no public, non-static set method)
 public Object getContextBean() 
    Returns the JavaBean associated with this context.
 abstract public Pointer getContextPointer()
    Returns a Pointer for the context bean.
 public DecimalFormatSymbols getDecimalFormatSymbols(String name) 
 public AbstractFactory getFactory() 
    Returns the AbstractFactory installed on this context. If none has been installed and this context has a parent context, returns the parent's factory. Otherwise returns null.
 public Functions getFunctions() 
    Returns the set of functions installed on the context.
 public IdentityManager getIdentityManager() 
    Returns this context's identity manager. If none has been installed, returns the identity manager of the parent context.
 public KeyManager getKeyManager() 
    Returns this context's key manager. If none has been installed, returns the key manager of the parent context.
 public Locale getLocale() 
    Returns the locale set with setLocale. If none was set and the context has a parent, returns the parent's locale. Otherwise, returns Locale.getDefault().
 public Pointer getNamespaceContextPointer() 
 public String getNamespaceURI(String prefix) 
    Given a prefix, returns a registered namespace URI. If the requested prefix was not defined explicitly using the registerNamespace method, JXPathContext will then check the context node to see if the prefix is defined there. See setNamespaceContextPointer .
 public JXPathContext getParentContext() 
    Returns the parent context of this context or null.
 abstract public Pointer getPointer(String xpath)
    Traverses the xpath and returns a Pointer. A Pointer provides easy access to a property. If the xpath matches no properties in the graph, the pointer will be null.
 public Pointer getPointerByID(String id) 
    Locates a Node by its ID.
 public Pointer getPointerByKey(String key,
    String value) 
    Locates a Node by a key value.
 abstract public JXPathContext getRelativeContext(Pointer pointer)
    Returns a JXPathContext that is relative to the current JXPathContext. The supplied pointer becomes the context pointer of the new context. The relative context inherits variables, extension functions, locale etc from the parent context.
 abstract public Object getValue(String xpath)
    Evaluates the xpath and returns the resulting object. Primitive types are wrapped into objects.
 abstract public Object getValue(String xpath,
    Class requiredType)
    Evaluates the xpath, converts the result to the specified class and returns the resulting object.
 public Variables getVariables() 
    Returns the variable pool associated with the context. If no such pool was specified with the setVariables() method, returns the default implementation of Variables, BasicVariables .
 public boolean isLenient() 
 abstract public Iterator iterate(String xpath)
    Traverses the xpath and returns an Iterator of all results found for the path. If the xpath matches no properties in the graph, the Iterator will be empty, but not null.
 abstract public Iterator iteratePointers(String xpath)
    Traverses the xpath and returns an Iterator of Pointers. A Pointer provides easy access to a property. If the xpath matches no properties in the graph, the Iterator be empty, but not null.
 public static JXPathContext newContext(Object contextBean) 
    Creates a new JXPathContext with the specified object as the root node.
 public static JXPathContext newContext(JXPathContext parentContext,
    Object contextBean) 
    Creates a new JXPathContext with the specified bean as the root node and the specified parent context. Variables defined in a parent context can be referenced in XPaths passed to the child context.
 public  void registerNamespace(String prefix,
    String namespaceURI) 
    Registers a namespace prefix.
 abstract public  void removeAll(String xpath)
    Removes all elements of the object graph described by the xpath.
 abstract public  void removePath(String xpath)
    Removes the element of the object graph described by the xpath.
 public List selectNodes(String xpath) 
    Finds all nodes that match the specified XPath.
 public Object selectSingleNode(String xpath) 
    Finds the first object that matches the specified XPath. It is equivalent to getPointer(xpath).getNode(). Note, that this method produces the same result as getValue() on object models like JavaBeans, but a different result for DOM/JDOM etc., because it returns the Node itself, rather than its textual contents.
 public  void setDecimalFormatSymbols(String name,
    DecimalFormatSymbols symbols) 
    Sets DecimalFormatSymbols for a given name. The DecimalFormatSymbols can be referenced as the third, optional argument in the invocation of format-number (number,format,decimal-format-name) function. By default, JXPath uses the symbols for the current locale.
 public  void setFactory(AbstractFactory factory) 
    Install an abstract factory that should be used by the createPath() and createPathAndSetValue() methods.
 public  void setFunctions(Functions functions) 
    Install a library of extension functions.
 public  void setIdentityManager(IdentityManager idManager) 
    Install an identity manager that will be used by the context to look up a node by its ID.
 public  void setKeyManager(KeyManager keyManager) 
    Install a key manager that will be used by the context to look up a node by a key value.
 public  void setLenient(boolean lenient) 
    If the context is in the lenient mode, then getValue() returns null for inexistent paths. Otherwise, a path that does not map to an existing property will throw an exception. Note that if the property exists, but its value is null, the exception is not thrown.

    By default, lenient = false

 public  void setLocale(Locale locale) 
    Set the locale for this context. The value of the "lang" attribute as well as the the lang() function will be affected by the locale. By default, JXPath uses Locale.getDefault()
 public  void setNamespaceContextPointer(Pointer namespaceContextPointer) 
    Namespace prefixes can be defined implicitly by specifying a pointer to a context where the namespaces are defined. By default, NamespaceContextPointer is the same as the Context Pointer, see getContextPointer()
 abstract public  void setValue(String xpath,
    Object value)
    Modifies the value of the property described by the supplied xpath. Will throw an exception if one of the following conditions occurs:
    • The xpath does not in fact describe an existing property
    • The property is not writable (no public, non-static set method)
 public  void setVariables(Variables vars) 
    Installs a custom implementation of the Variables interface.