Home > Articles > Programming > Java

  • Print
  • + Share This
This chapter is from the book

This chapter is from the book

23.3 Parsing XML Documents with SAX 2.0

DOM processing is relatively straightforward since the DOM classes do all the "real" parsing—you just have to look through the parsed result for the data you want. However, DOM can be quite wasteful if you only care about a small part of the document. For example, suppose that you want to extract the first word from an XML document representing an entire dictionary. DOM would require you to parse and store the entire XML document (which could be huge in this case). With SAX, you need only store the parts you care about and can stop parsing whenever you want. On the other hand, SAX is a bit more work. The idea is that the system tells you when certain parsing events such as finding a start tag (<language rating="good">), an end tag (</language>), or a tag body (e.g., Java between the aforementioned start and end tags). You have to decide what to do when these events occur. Are you a JSP programmer? Does this process sound familiar? It should—SAX processing is very similar to the way you go about defining custom JSP tag libraries (Section 20.7).

Installation and Setup

SAX is not a standard part of either Java 2 Standard Edition or the servlet and JSP APIs. So, your first step is to download the appropriate classes and configure them for use in your programs. Here is a summary of what is required.

  1. Download a SAX-compliant parser. The parser provides the Java classes that follow the SAX 2 API as specified by the WWW Consortium. You can obtain a list of XML parsers in Java at http://www.xml.com/ pub/rg/Java_Parsers. We use the Apache Xerces-J parser in this book. See http://xml.apache.org/xerces-j/. This parser comes with the complete SAX API in Javadoc format.

  2. Download the Java API for XML Processing (JAXP). This API provides a small layer on top of SAX that lets you plug in different vendor's parsers without making any changes to your basic code. See http://java.sun.com/xml/.

  3. Set your CLASSPATH to include the SAX classes. In the case of Apache Xerces, you need to include xerces_install_dir\ xerces.jar. For example, on Windows you would do

    set CLASSPATH=xerces_install_dir\xerces.jar;%CLASSPATH%

    If you wanted to use DOM from servlets and JSP, you would copy the appropriate JAR file to the server's lib directory (if supported), unpack the JAR file (using jar -xvf) into the server's classes directory, or explicitly change the server's CLASSPATH, usually by modifying the server startup script.

  4. Set your CLASSPATH to include the JAXP classes. These classes are in jaxp_install_dir/jaxp.jar. For example, on Unix/Linux and the C shell, you would do

    setenv CLASSPATH jaxp_install_dir/jaxp.jar:$CLASSPATH

    For use from servlets and JSP, see the preceding step.

  5. Bookmark the SAX 2 and JAXP APIs. You can browse the official API at http://www.megginson.com/SAX/Java/ javadoc/, but the API that comes with Apache Xerces is easier to use because it is on your local system and is integrated with the DOM and JAXP APIs. More information on SAX can be found at http://www.megginson.com/SAX/.

Parsing

With SAX processing, there are two high-level tasks: creating a content handler and invoking the parser with the designated content handler. The following list summarizes the detailed steps needed to accomplish these tasks.

  1. Tell the system which parser you want to use. This can be done in a number of ways: through the javax.xml.parsers.SAXParserFactory system property, through jre_dir/lib/ jaxp.properties, through the J2EE Services API and the class specified in META-INF/services/javax.xml.parsers.SAXParserFactory, or with a system-dependent default parser. The system property is the easiest method. For example, the following code permits users to specify the parser on the command line with the -D option to java, and uses the Apache Xerces parser otherwise.

    public static void main(String[] args) {
      String jaxpPropertyName =
        "javax.xml.parsers.SAXParserFactory";
      if (System.getProperty(jaxpPropertyName) == null) {
        String apacheXercesPropertyValue =
          "org.apache.xerces.jaxp.SAXParserFactoryImpl";
        System.setProperty(jaxpPropertyName,
                           apacheXercesPropertyValue);
      }
      ...
    }
  2. Create a parser instance. First make an instance of a parser factory, then use that to create a parser object.

    SAXParserFactory factory = SAXParserFactory.newInstance();
    SAXParser parser = factory.newSAXParser();

    Note that you can use the setNamespaceAware and setValidating methods on the SAXParserFactory to make the parser namespace aware and validating, respectively.

  3. Create a content handler to respond to parsing events. This handler is typically a subclass of DefaultHandler. You override any or all of the following placeholders

    • startDocument, endDocument

      Use these methods to respond to the start and end of the document; they take no arguments.

    • startElement, endElement

      Use these methods to respond to the start and end tags of an element. The startElement method takes four arguments: the namespace URI (a String; empty if no namespace), the namespace or prefix (a String; empty if no namespace), the fully qualified element name (a String; i.e., "prefix:mainName" if there is a namespace; "mainName" otherwise), and an Attributes object representing the attributes of the start tag. The endElement method takes the same arguments except for the attributes (since end tags are not permitted attributes).

    • characters, ignoreableWhitespace

      Use these methods to respond to the tag body. They take three arguments: a char array, a start index, and an end index. A common approach is to turn the relevant part of the character array into a String by passing all three arguments to the String constructor. Non-whitespace data is always reported to the characters method. Whitespace is always reported to the ignoreableWhitespace method a parser is run in validating mode, but can be reported to either method otherwise.

  4. Invoke the parser with the designated content handler. You invoke the parser by calling the parse method, supplying an input stream, URI (represented as a string), or org.xml.sax.InputSource along with the content handler.

    parser.parse(filename, handler);

The content handler does the rest.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020