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>– <title>Java for programmers– </title>

• </book>• <book><title>Java for morons</title></book>

– </books>

• </product>

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!).

DTD’s

• Document Type Defn Language

• <?xml version=“1.0” encoding=“ISO=8859-1” standalone=“yes” ?>

• <!DOCTYPE nameOfItem [

• elements follow ]>

Doing the DOCType

<!DOCTYPE Cart [

<!ELEMENT Product (Name, price,…)>

<!ELEMENT Product (#PCDATA)>

<!ELEMENT Name (#PCDATA)>

<!ELEMENT Price (#PCDATA)>

]> <Cart> ….products </Cart>

Shopping Cart

<Cart><Product>

<Name> Image Processing in Java</Name>

<Price> $45.00</Price>

….more stuff

</Product>

</Cart>

Read XML

Build an XML reader for reading HTML!

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();• }

readXml

• public static Object readXml() {

• XMLDecoder e =

• new XMLDecoder(Futil.getFileInputStream("select an xml file"));

• return e.readObject();

• }

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();• }

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

What good is putting out bytes?

• serializable objects

• compression can be employed

• store images, audio, multi-media, etc.

Why would you want anything else?

• Might be good to stash XML

• Human readable text

• Good for testing/debugging

How do I store strings?

• void put(java.lang.String key, java.lang.String value)

•  java.lang.String get(java.lang.String key, java.lang.String def)

• def – default value

how do I get the user Prefs?

• static Preferences userRoot() Returns the root preference node for the calling user

How do I get the system prefs?

• public static Preferences systemRoot() Returns the root preference node for the system.

Example of getting user data

• private static String getData() {

• Preferences p = Preferences.userRoot();

• return p.get("com.docjava.foo", null);

• }

Example of Writing user data

• private static void putData(String s) {

• Preferences p = Preferences.userRoot();

• p.put("com.docjava.foo", s);

• }

• check futils.PreferencesExample

How do you set up the prefs?

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.