This package is a light-weight Julia wrapper of libxml2, which provides a minimal interface that covers functionalities that are commonly needed:
Like other Julia packages, you may checkout LightXML from the General registry, as
Note: This package relies on the library libxml2 to work, which is shipped with Mac OS X and many Linux systems. So this package may work out of the box. If not, you may check whether libxml2 has been in your system and whether libxml2.so (for Linux) or libxml2.dylib (for Mac) is on your library search path.
The following examples show how you may use this package to accomplish common tasks.
Suppose you have an XML file
ex1.xml as below
Everyday Italian Giada De Laurentiis 2005 30.00 Harry Potter J K. Rowling 2005 29.99
Here is the code to parse this file:
using LightXML # parse ex1.xml: # xdoc is an instance of XMLDocument, which maintains a tree structure xdoc = parse_file("ex1.xml") # get the root element xroot = root(xdoc) # an instance of XMLElement # print its name println(name(xroot)) # this should print: bookstore # traverse all its child nodes and print element names for c in child_nodes(xroot) # c is an instance of XMLNode println(nodetype(c)) if is_elementnode(c) e = XMLElement(c) # this makes an XMLElement instance println(name(e)) end end #= If the remainder of the script does not use the document or any of its children, you can call free here to deallocate the memory. The memory will only get deallocated by calling free or by exiting julia -- i.e., the memory allocated by libxml2 will not get freed when the julia variable wrapping it goes out of scope. =# free(xdoc)
There are actually five child nodes under
: the 1st, 3rd, 5th children are text nodes (any space between node elements are captured by text nodes), while the 2nd and 4th nodes are element nodes corresponding to the
One may use the function
nodetype to determine the type of a node, which returns an integer following the table here. In particular, 1 indicates element node and 3 indicates text node.
If you only care about child elements, you may use
child_elements instead of
ces = collect(child_elements(xroot)) # get a list of all child elements @assert length(ces) == 2 # if you know the child element tagname, you can instead get a list as ces = get_elements_by_tagname(xroot, "book") # or shorthand: ces = xroot["book"] e1 = ces # the first book element # print the value of an attribute println(attribute(e1, "category")) # find the first title element under e1 t = find_element(e1, "title") # retrieve the value of lang attribute of t a = attribute(t, "lang") # a <- "en" # retrieve the text content of t r = content(t) # r <- "Everyday Italian"
One can also traverse all attributes of an element (
for a in attributes(e1) # a is an instance of XMLAttr n = name(a) v = value(a) println("$n = $v") end
Another way to access attributes is to turn them into a dictionary using
ad = attributes_dict(e1) v = ad["category"] # v <-- "COOKING"
Note: The functions
attributes return light weight iterators -- so that one can use them with for-loop. To get an array of all items, one may use the
collect function provided by Julia.
This package allows you to construct an XML document programmatically. For example, to create an XML document as
Massachusetts Illinois California
You may write:
# create an empty XML document xdoc = XMLDocument() # create & attach a root node xroot = create_root(xdoc, "States") # create the first child xs1 = new_child(xroot, "State") # add the inner content add_text(xs1, "Massachusetts") # set attribute set_attribute(xs1, "tag", "MA") # likewise for the second child xs2 = new_child(xroot, "State") add_text(xs2, "Illinois") # set multiple attributes using a dict set_attributes(xs2, Dict("tag"=>"IL", "cap"=>"Springfield")) # now, the third child xs3 = new_child(xroot, "State") add_text(xs3, "California") # set attributes using keyword arguments set_attributes(xs3; tag="CA", cap="Sacramento")
Note: When you create XML documents and elements directly you need to take care not to leak memory; memory management in the underlying libxml2 library is complex and LightXML currently does not integrate well with Julia's garbage collection system. You can call
free on an XMLDocument, XMLNode or XMLElement but you must take care not to reference any child elements after they have been manually freed.
With this package, you can easily export an XML file to a string or a file, or show it on the console, as
# save to an XML file save_file(xdoc, "f1.xml") # output to a string s = string(xdoc) # print to the console (in a pretty format as in an XML file) print(xdoc)
show functions are specialized for both
Main types of this package
XMLDocument: represent an XML document (in a tree)
XMLElement: represent an XML element (
child_elementsgive you this)
XMLNode: represent a generic XML node (
child_nodesgive you this)
XMLAttr: represent an XML attribute
Note: If an
x is actually an element node, one may construct an
XMLElement instance by
A list of API functions:
# Let xdoc be a document, x be a node/element, e be an element root(xdoc) # get the root element of a document nodetype(x) # get an integer indicating the node type name(x) # get the name of a node/element content(x) # get text content of a node/element # if x is an element, this returns all text (concatenated) within x is_elementnode(x) # whether x is an element node is_textnode(x) # whether x is a text node is_cdatanode(x) # whether x is a CDATA node is_commentnode(x) # whether x is a comment node has_children(e) # whether e has child nodes has_attributes(e) # whether e has attributes child_nodes(x) # iterator of all child nodes of a node/element x child_elements(e) # iterator of all child elements of e attributes(e) # iterator of all attributes of e attributes_dict(e) # a dictionary of all attributes of e, # which maps names to corresponding values has_attribute(e, name) # whether a named attribute exists for e # get the value of a named attribute # when the attribute does not exist, it either # throws an exception (when required is true) # or returns nothing (when required is false) attribute(e, name; required=false) find_element(e, name) # the first element of specified name under e # return nothing is no such an element is found get_elements_by_tagname(e, name) # a list of all child elements of e with # the specified name. Equivalent to e[name] string(e) # format an XML element into a string show(io, e) # output formatted XML element unlink(x) # remove a node or element from its current context # (unlink does not free the memory for the node/element) free(xdoc) # release memory for a document and all its children free(x) # release memory for a node/element and all its children
xdoc = XMLDocument() # create an empty XML document e = new_element(name) # create a new XML element # this does not attach e to a tree t = new_textnode(content) # create a new text node # this does not attach t to a tree set_root(xdoc, e) # set element e as the root of xdoc add_child(parent, x) # add x as a child of a parent element e = create_root(xdoc, name) # create a root element and set it as root # equiv. to new_element + set_root e = new_child(parent, name) # create a new element and add it as a child # equiv. to new_element + add_child add_text(e, text) # add text content to an element # equiv. to new_textnode + add_child set_content(e, text) # replace text content of an element add_cdata(xdoc, e, text) # add cdata content to an element # equiv. to new_cdatanode + add_child set_attribute(e, name, value) # set an attribute of an element # this returns the added attribute # as an instance of XMLAttr set_attributes(e, attrs) # set multiple attributes in one call # attrs can be a dictionary or # a list of pairs as (name, value) # one can also use keyword arguments to set attributes to an element set_attributes(e, key1="val1", key2="val2", ...)
xdoc = parse_file(filename) # parse an XML file xdoc = parse_file(filename, # parse an XML file with a specified encoding and parser options, encoding, options) # see http://xmlsoft.org/html/libxml-parser.html#xmlReadFile # and http://xmlsoft.org/html/libxml-parser.html#xmlParserOption xdoc = parse_string(str) # parse an XML doc from a string save_file(xdoc, filename) # save xdoc to an XML file string(xdoc) # formatted XML doc to a string show(io, xdoc) # output formatted XML document
16 days ago