public class XmlIO
extends java.lang.Object
| Modifier and Type | Class and Description |
|---|---|
static class |
XmlIO.Read<T>
Implementation of
read(). |
static class |
XmlIO.ReadFiles<T>
Implementation of
readFiles(). |
static class |
XmlIO.Write<T>
Implementation of
write(). |
| Constructor and Description |
|---|
XmlIO() |
| Modifier and Type | Method and Description |
|---|---|
static <T> XmlIO.Read<T> |
read()
Reads XML files as a
PCollection of a given type mapped via JAXB. |
static <T> XmlIO.ReadFiles<T> |
readFiles()
Like
read(), but reads each file in a PCollection of FileIO.ReadableFile, which
allows more flexible usage via different configuration options of FileIO.match() and
FileIO.readMatches() that are not explicitly provided for read(). |
static <T> XmlIO.Write<T> |
write()
A
FileBasedSink that outputs records as XML-formatted elements. |
public static <T> XmlIO.Read<T> read()
PCollection of a given type mapped via JAXB.
The XML files must be of the following form, where root and record are XML
element names that are defined by the user:
<root>
<record> ... </record>
<record> ... </record>
<record> ... </record>
...
<record> ... </record>
</root>
Basically, the XML document should contain a single root element with an inner list
consisting entirely of record elements. The records may contain arbitrary XML content; however,
that content must not contain the start <record> or end </record> tags.
This restriction enables reading from large XML files in parallel from different offsets in the
file.
Root and/or record elements may additionally contain an arbitrary number of XML attributes.
Additionally users must provide a class of a JAXB annotated Java type that can be used convert
records into Java objects and vice versa using JAXB marshalling/unmarshalling mechanisms.
Reading the source will generate a PCollection of the given JAXB annotated Java type.
Optionally users may provide a minimum size of a bundle that should be created for the source.
Example:
PCollection<String> output = p.apply(XmlIO.<Record>read()
.from(file.toPath().toString())
.withRootElement("root")
.withRecordElement("record")
.withRecordClass(Record.class));
By default, UTF-8 charset is used. To specify a different charset, use XmlIO.Read.withCharset(java.nio.charset.Charset).
Currently, only XML files that use single-byte characters are supported. Using a file that contains multi-byte characters may result in data loss or duplication.
T - Type of the objects that represent the records of the XML file. The PCollection generated by this source will be of this type.public static <T> XmlIO.ReadFiles<T> readFiles()
read(), but reads each file in a PCollection of FileIO.ReadableFile, which
allows more flexible usage via different configuration options of FileIO.match() and
FileIO.readMatches() that are not explicitly provided for read().
For example:
PCollection<ReadableFile> files = p
.apply(FileIO.match().filepattern(options.getInputFilepatternProvider()).continuously(
Duration.standardSeconds(30), afterTimeSinceNewOutput(Duration.standardMinutes(5))))
.apply(FileIO.readMatches().withCompression(GZIP));
PCollection<String> output = files.apply(XmlIO.<Record>readFiles()
.withRootElement("root")
.withRecordElement("record")
.withRecordClass(Record.class));
public static <T> XmlIO.Write<T> write()
FileBasedSink that outputs records as XML-formatted elements. Writes a PCollection of records from JAXB-annotated classes to a single file location.
Given a PCollection containing records of type T that can be marshalled to XML elements, this Sink will produce a single file consisting of a single root element that contains all of the elements in the PCollection.
XML Sinks are created with a base filename to write to, a root element name that will be used for the root element of the output files, and a class to bind to an XML element. This class will be used in the marshalling of records in an input PCollection to their XML representation and must be able to be bound using JAXB annotations (checked at pipeline construction time).
XML Sinks can be written to using the XmlIO.Write transform:
p.apply(XmlIO.<Type>write()
.withRecordClass(Type.class)
.withRootElement(root_element)
.toFilenamePrefix(output_filename));
For example, consider the following class with JAXB annotations:
@XmlRootElement(name = "word_count_result")
@XmlType(propOrder = {"word", "frequency"})
public class WordFrequency {
private String word;
private long frequency;
public WordFrequency() { }
public WordFrequency(String word, long frequency) {
this.word = word;
this.frequency = frequency;
}
public void setWord(String word) {
this.word = word;
}
public void setFrequency(long frequency) {
this.frequency = frequency;
}
public long getFrequency() {
return frequency;
}
public String getWord() {
return word;
}
}
The following will produce XML output with a root element named "words" from a PCollection of WordFrequency objects:
p.apply(XmlIO.<WordFrequency>write()
.withRecordClass(WordFrequency.class)
.withRootElement("words")
.toFilenamePrefix(output_file));
The output of which will look like:
<words>
<word_count_result>
<word>decreased</word>
<frequency>1</frequency>
</word_count_result>
<word_count_result>
<word>War</word>
<frequency>4</frequency>
</word_count_result>
<word_count_result>
<word>empress'</word>
<frequency>14</frequency>
</word_count_result>
<word_count_result>
<word>stoops</word>
<frequency>6</frequency>
</word_count_result>
...
</words>
By default the UTF-8 charset is used. This can be overridden, for example:
p.apply(XmlIO.<Type>write()
.withRecordClass(Type.class)
.withRootElement(root_element)
.withCharset(StandardCharsets.ISO_8859_1)
.toFilenamePrefix(output_filename));