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https://codeberg.org/Mercury-IM/Smack
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2.4 KiB
2.4 KiB
Smack Providers
Providers are responsible for parsing the XMPP XML stream into new Java objects.
Provider Design
Assume you want to parse the following stanza extension element
<myExtension attrFoo='fourthyTwo'>
<myElement>Foo is greater then Bar</myElement>
<myInfo alpha='true' delta='-1337'/>
</myExtension>
then the related provider would look like this
public MyExtension parse(XmlPullParser parser, int initialDepth) {
MyElement myElement = null;
MyInfo myInfo = null;
String attrFoo = parser.getAttributeValue("", "attrFoo");
// Main parsing loop, use a loop label instead of "boolean done"
outerloop: while(true) {
// Make sure to have already parse all attributes of the outermost element,
// i.e. 'attrFoo' of 'myExtension' in this example. Then advance the parser
int event = parser.next();
// Use switch/case of int instead of a if/else-if cascade
switch (event) {
case XmlPullParser.START_TAG:
// Determine the name of the element which start tag we are seeing
String name = parser.getName();
// We can use switch/case of Strings since Java7, make use of its advantages
// and collect the values of the sub elements. If the sub elements are more
// complex then those of this example, consider creating extra *private static*
// parsing methods for them.
switch(name) {
case "myElement":
// You should only use XmlPullParser.nextText() when the element is
// required to have a text.
myElement = new MyElement(parser.nextText());
break;
case "myInfo";
// Use ParserUtils to parse Java primitives
boolenan alpha = ParserUtils.getBooleanAttribute(parser, "alpha");
int delta = ParserUtils.getIntegerAttribute(parser, "delta");
myInfo = new MyInfo(alpha, delta);
break;
}
break;
case XmlPullParser.END_TAG:
// The abort condition with the break labeled loop statement
if (parser.getDepth() == initialDepth) {
break outerloop;
}
break;
}
}
// Create the actual class at the very end, design the classes as immutable as possible
return new MyExtension(attrFoo, myElement, myInfo);
}
Common Pitfalls
Use a long
instead of int
when the XML schema says xs:unsignedInt
, because Java's int
range is to small for this XML numeric data type.