Introduction to XML and XML With Java : If you are looking for sample programs to parse a XML file using DOM/SAX parser or looking for a program to generate a XML file please proceed directly to programs. Java Technology and XML- Part 3: Performance Improvement Tips. Articles Index. By Thierry Violleau March 2. Neither Java nor XML Technology need an introduction, nor the synergy between the two: . As of today, no less than six extensions to the Java Platform empower the developer when building XML- based applications: Java API for XML Processing (JAXP)Java API for XML/Java Binding (JAXB)Long Term Java. Beans Persistence. Java API for XML Messaging (JAXM)Java API for XML RPC (JAX RPC)Java API for XML Registry (JAXR)The first of the three articles in this series gave an overview of the different APIs available to the developer by presenting some sample programs. The Xalan-Java download includes xercesImpl.jar from Xerces. Once the subverion client is installed on your local machine you can use the command line client program svn to get the. Installing Xalan-C++: Apache Foundation: Xalan Project: Xerces Project. The Xerces-C sources are expected to be found in a directory named xerces-src. When building the Xalan-C library and sample programs. Parsing XML with Xerces-C C++ API. Get ambigious segfault otherwise. Processing XML with Xerces and SAX. The sample program step4 demonstrates this using the resolver SimpleEntityResolver. This class uses an internal map to match grammar URIs to local resources. Note that resolveEntity(). The differences in performance were addressed in the second article. This third article gives tips on improving the performance of XML- based applications from a programmatic and architectural point of view. XML processing is very CPU, memory, and I/O or network intensive. XML documents are text documents that need to be parsed before any meaningful application processing can be performed. The parsing of an XML document may result either in a stream of events if the SAX API is used, or in an in- memory document model if the DOM API is used. During parsing, a validating parser may additionally perform some validity checking of the document against a predefined schema (a Document Type Definition or an XML Schema). Processing an XML document means recognizing, extracting and directly processing the element contents and attribute values or mapping them to other business objects that are processed further on. Before an application can apply any business logic, the following steps must take place: Parsing. ![]() Optionally, validating (which implies first parsing the schema)Recognizing. Extracting. Optionally, mapping. Parsing XML documents implies a lot of character encoding and decoding and string processing. Then, depending on the chosen API, recognition and extraction of content may correspond to walking through a tree data structure, or catching the events generated by the parser and processing them according to some context. If an application uses XSLT to preprocess an XML document, even more processing is added before the real business logic work can take place. Using the DOM API implies the creation in memory of a representation of the document as a DOM tree. If the document is large, so is the DOM tree and the memory consumption. The physical structure and the logical structure of an XML document may be different. An XML document may contain references to external entities which are substituted in the document content while parsing and prior to validating. Those external entities and the schema itself (such as DTD) may be located on remote systems, especially if the document itself is originating from another system. In order to proceed with the parsing and the validation, the external entities must first be loaded (downloaded). Documents with a complex physical structure may therefore be very I/O or network intensive. In this article, we will give some tips for improving performance when processing XML documents, articulated around improving the CPU, memory, and I/O or network consumption. Using the Most Appropriate API: Choosing Between SAX and DOMBoth DOM and SAX have features that make them more suitable for certain tasks than others: Table 1: SAX and DOM features. SAXDOMEvent based model. Tree data structure. Serial access (flow of events)Random access (in- memory data structure)Low memory usage (only events are generated)High memory usage (the document is loaded into memory)To process parts of the document (catching relevant events)To edit the document (processing the in- memory data structure)To process the document only once (transient flow of events)To process multiple times (document loaded in memory)Omitting the impact of memory consumption on overall system performance, processing using the DOM API is usually slower than processing using the SAX API, mainly because the DOM API may have to load the whole document in- memory first in order to allow it to be edited or data to be easily retrieved, while the SAX API allows immediate processing as the document is being parsed. Therefore, DOM should be used when the source document is to be edited or processed multiple times. SAX is very convenient when you want to extract information from an XML document (an element content or an attribute value) regardless of its overall context - - its position in the XML document tree, or when the document structure maps exactly to the business object structure. Otherwise, keeping track of the element nesting may be very tedious and one may better end up using DOM. Nevertheless, when the source document is to be mapped to a business object which is not primarily represented as a DOM tree, it's recommended to use SAX to map directly to the business object, avoiding an intermediate resource- consuming representation. Of course, if the business object has a direct representation in Java, technologies like XML Data Binding (JAXB) can be used. Since high level technologies like XSLT rely on lower level technologies like SAX and DOM, the performance when using those technologies may be impacted by their use of SAX or DOM. JAXP provides support for XSLT engine implementations that accept source input and result output in the form of SAX events. When building complex XML processing pipelines, one can use JAXP SAXTransformer. Factory to process the result of another style sheet transformation with a style sheet. Working with SAX events until the last stage in the pipeline will optimize performance by avoiding the creation of in- memory data structures like DOM trees. Considering Alternative APIs. JDOM is not a wrapper around DOM, although it shares the same purpose as DOM with regard to XML. It has been made generic enough to address any document model. JDOM has been optimized for Java and moreover, by the use of the Java Collection API, it has been made straightforward for the Java developer. JDOM documents can be built directly from, and converted to, SAX events and DOM trees, allowing JDOM to be seamlessly integrated in XML processing pipelines and in particular as the source or result of XSLT transformations. API very similar to JDOM. It additionally comes with a tight integration to Xpath: the org. Node interface for example defines methods to select nodes according to an Xpath expression. ![]() This section provides a list of sample programs provided in Xerces2 Java 2.11.0 XML Schema 1.1 Beta version that you can use to parse and validate XML documents. Installing Xerces - Windows Troubleshooting. Installing Xerces on a Windows machine can be troublesome, particularly if you've never used Java. Now try running the Xerces sample program as above. Sun donated Project X which became Apache Crimson. Xerces 2 is a new third parser which is a rewrite. It has goals such as maintainability. The JAXP 1.2.0 RI contains two sample programs (DOMEcho and SAXLocalNameCount). Handlers can be registered to be called back during parsing when Xpath expressions are matched, allowing you to immediately process and dispose of parts of the document without waiting for all the document to be parsed and loaded into memory. If a document model fits the core data structure of an application, JDOM and dom. Additionally, as opposed to DOM 1 , JDOM or dom. Using alternative APIs like JDOM and dom. API through the support of the Java Collection API is more straightforward. Since it is lightweight and optimized for Java, you may often expect a sensitive gain in performance. Be Aware of the Differences in the Implementations. As we highlighted in the second part of this series, implementations differ. Some emphasize functionality, others performance. The plugability feature of JAXP allows the developer to swap between implementations and select the most appropriate one to achieve the application requirements. As an example, when using DOM, a common complaint is the lack of support in the API itself for serialization (that is, transformation of a DOM tree to a XML document). Therefore, it's tempting to step out of the standard API and call implementation- dependent serialization features at the cost of losing JAXP's plugability benefits. Below are code samples for serializing a DOM tree to an XML stream with both Xerces and Crimson. Code Sample 1: Serialization with Xerces relies on a separate API which is packaged along with the DOM implementation. Document document = .. The identity transformer just copies the source tree to the result tree and applies the specified output method. To output in XML, the output method needs only to be set to xml. It solves the problem in an easy and implementation- independent way. Code Sample 3: Implementation- independent serialization with the identity transformer (no argument passed to the factory method Transformer. Factory. new. Instance) import javax. Document document = .. It's worth capitalizing on so that later on, the underlying parser implementations can be swapped easily without requiring any application code changes. Tuning the Underlying Implementations. The JAXP API defines methods to set/get features and properties in order to configure the underlying implementations. Apart from the standard properties and features such as the http: //xml. For example, Xerces defines the feature http: //apache. DOM mode (enabled by default); in this mode, the DOM tree nodes are lazily evaluated, their creation is deferred: they are created only when they are accessed. The construction of a DOM tree from an XML document returns faster and only the accessed nodes get expanded. This feature is particularly useful when only parts of the DOM tree are to be processed. Setting specific features and properties should be done with care to preserve the interchangeability of the underlying implementation. When a feature or a property is not supported or not recognized by the underlying implementation, a SAXNot. Recognized. Exception, a SAXNot. Supported. Exception or an Illegal. Argument. Exception may be thrown by the SAXParser. Factory, the XMLReader or the Document. Builder. Factory. Avoid grouping unrelated features and properties, especially standard versus specific ones, in a single try/catch block; handle the exceptions independently so that optional specific features or properties don't prevent switching to a different implementation.
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