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XML

XML. What is XML? Why do I need it? How do I use it?. What is XML?. XML – extensible markup language. A well-formed, parsable language able to convey structured textual data. A meta language for defining hierarchical markup languages. Sample XML . <product> <books> <book>

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XML

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  1. XML What is XML? Why do I need it? How do I use it?

  2. What is XML? • XML – extensible markup language. • A well-formed, parsable language able to convey structured textual data. • A meta language for defining hierarchical markup languages

  3. Sample XML • <product> • <books> • <book> • <title>Java for programmers • </title> • </book> • <book><title>Java for morons</title></book> • </books> • </product>

  4. How do I spec correct xml? • You don’t have to (the parser is tolerent of bad xml) • You can do syntax checking on parsing using • The old way DTD • The new way XML Schema (is xml for defining xml!).

  5. DTD’s • Document Type Defn Language • <?xml version=“1.0” encoding=“ISO=8859-1” standalone=“yes” ?> • <!DOCTYPE nameOfItem [ • elements follow ]>

  6. Doing the DOCType <!DOCTYPE Cart [ <!ELEMENT Product (Name, price,…)> <!ELEMENT Product (#PCDATA)> <!ELEMENT Name (#PCDATA)> <!ELEMENT Price (#PCDATA)> ]> <Cart> ….products </Cart>

  7. Shopping Cart <Cart> <Product> <Name> Image Processing in Java</Name> <Price> $45.00</Price> ….more stuff </Product> </Cart>

  8. Read XML Build an XML reader for reading HTML!

  9. writeXml • xml.utils has: • public static void writeXml(Serializable object) { • XMLEncoder e = new XMLEncoder( • futils.Futil.getFileOutputStream("select xml output file")); • e.writeObject(object); • e.close(); • }

  10. readXml • public static Object readXml() { • XMLDecoder e = • new XMLDecoder(Futil.getFileInputStream("select an xml file")); • return e.readObject(); • }

  11. xml.Utils • public static String toXml(Serializable object) { • ByteArrayOutputStream baos = new ByteArrayOutputStream(); • XMLEncoder e = new XMLEncoder(baos); • e.writeObject(object); • e.flush(); • return baos.toString(); • }

  12. Preferences • package: java.util.prefs.Preferences • store and retrieve user and system data. • available since jdk1.4 • putByteArray(java.lang.String key, byte[] value) • public  byte[] getByteArray(java.lang.String key, byte[] def) • def=default value

  13. What good is putting out bytes? • serializable objects • compression can be employed • store images, audio, multi-media, etc.

  14. Why would you want anything else? • Might be good to stash XML • Human readable text • Good for testing/debugging

  15. How do I store strings? • void put(java.lang.String key, java.lang.String value) • java.lang.Stringget(java.lang.String key, java.lang.String def) • def – default value

  16. how do I get the user Prefs? • static PreferencesuserRoot() Returns the root preference node for the calling user

  17. How do I get the system prefs? • public static PreferencessystemRoot() Returns the root preference node for the system.

  18. Example of getting user data • private static String getData() { • Preferences p = Preferences.userRoot(); • return p.get("com.docjava.foo", null); • }

  19. Example of Writing user data • private static void putData(String s) { • Preferences p = Preferences.userRoot(); • p.put("com.docjava.foo", s); • } • check futils.PreferencesExample

  20. How do you set up the prefs?

  21. Using the WebstartDialog • In the security package, • use Preferences to serialize an xml version of the webstartdialog….so that next • time you start, the old values are retained. • Use the user’s preferences. • add an xmlDecoder in the WebStartBean • The bean has the values…the dialog is the gui.

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