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| <h1>JXPath 2.0 Release Notes </h1> |
| <h2>New Functionality</h2> |
| <p>JXPath 2.0 is no longer using Xalan combined with a light-weight "DOM" |
| struture for interpretation of XPaths. The old model has some limitations. As |
| a result of this change, there are many more XPaths that will work properly |
| now. </p> |
| <h3>Pointers</h3> |
| <p>In addition to getting/setting values using XPaths, JXPath 2.0 can evaluate |
| an XPath into a Pointer or a set of Pointers. A Pointer is a simple value accessor |
| that can be used repeatedly to get/set value of an object in the graph. More |
| importantly, it can produce a new XPath that precisely describes the object's |
| location in the graph. For example, </p> |
| <blockquote> |
| <p><code>Pointer ptr = ctx.locateValue("employees[$i]/addresses[$j]"); |
| </code></p> |
| </blockquote> |
| <p>will produce a Pointer that has concrete values of <code>$i</code> and <code>$j</code>. |
| Therefore, </p> |
| <blockquote> |
| <p><code>ptr.asPath()</code> </p> |
| </blockquote> |
| <p>will produce something like </p> |
| <blockquote> |
| <p><code>"/employees[1]/addresses[3]"</code></p> |
| </blockquote> |
| <p>One possible application of these concrete paths is for names of form elements |
| on dynamically generated HTML pages. When the POST with the values for these |
| elements arrives to the server, all we need to do is call <code>JXPath.setValue()</code> |
| with the concrete XPaths and the corresponding values.</p> |
| <h3>Extension Functions</h3> |
| <p>JXPath 2.0 fully supports extension functions. Extension functions can be implemented |
| directly or as Java classes or packages. You can now use method calls and create |
| objects directly from XPath expressions. For example, here's how you can call |
| a method:</p> |
| <blockquote> |
| <p><code>"bestStudent($school, $grade)"</code></p> |
| </blockquote> |
| <p>This is equivalent to </p> |
| <blockquote> |
| <p><code>school.bestStudent(grade)</code></p> |
| </blockquote> |
| <p>To create a new object use the keyword "new":</p> |
| <blockquote> |
| <p><code>"'Current time is ' + java.util.Date.new()"</code></p> |
| </blockquote> |
| <p>To call a static method:</p> |
| <blockquote> |
| <p><code>"java.lang.System.getProperty('companyName')"</code></p> |
| </blockquote> |
| <p>You can also register functions with namespaces, which allow you to use abbreviated |
| syntax like:</p> |
| <blockquote> |
| <p><code>"sys:getProperty('companyName')"</code></p> |
| </blockquote> |
| <h3>Dynamic Property Access</h3> |
| <p>The new syntax for accessing dymanic properties (e.g. map values) is: </p> |
| <blockquote> |
| <p><code>"map[@name = expression]"</code></p> |
| </blockquote> |
| <p>You can still use the syntax introduced by JXPath 1.0, if the key is know upfront |
| and is a proper XPath identifier:</p> |
| <blockquote> |
| <p><code>"map/key"</code></p> |
| </blockquote> |
| <h3>Indexed Properties</h3> |
| <p>Indexed JavaBeans properties are now supported in accordance with the JavaBeans |
| specification. If indexed read/write methods are missing, JXPath attempts to modify |
| the collection directly.</p> |
| <h2>Performance</h2> |
| <p>JXPath 2.0 is a complete re-write of the implementation. The dependency on Xalan |
| has been eliminated. JXPath 2.0 features its own parser/compiler/interpreter |
| that are specifically tailored to the needs of Java object graph traversal. |
| </p> |
| <h3>Property Access</h3> |
| <p>JXPath 2.0 accesses object fields directly by name rather than "searching" |
| for them. For example if you have an object with a property that is a long array |
| followed by a property that is an int, JXPath 1.0 would enumerate through the |
| long array before it found the integer property. JXPath 2.0 jumps directly to |
| that variable.</p> |
| <h3>Cached Parse Results</h3> |
| <p>JXPath 2.0 caches results of compilation of XPaths. This way the overhead of |
| calling the parser/compiler is significantly reduced.</p> |
| <h3>Cached Intermediate Results</h3> |
| <p>JXPath 2.0 avoid multiple computations of the same intermediate expression. |
| For example, in <code>"//person[name |
| = $firstName + ' ' + $lastName]"</code> the concatenation of the string |
| will only be performed once.</p> |
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