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.Sink<T>
Implementation of
sink(java.lang.Class<T>) . |
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.Sink<T> |
sink(java.lang.Class<T> recordClass)
Outputs records as XML-formatted elements using JAXB.
|
static <T> XmlIO.Write<T> |
write()
Writes all elements in the input
PCollection to a single XML file using sink(java.lang.Class<T>) . |
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<Record> 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<Record> output = files.apply(XmlIO.<Record>readFiles()
.withRootElement("root")
.withRecordElement("record")
.withRecordClass(Record.class));
public static <T> XmlIO.Write<T> write()
PCollection
to a single XML file using sink(java.lang.Class<T>)
.
For more configurable usage, use sink(java.lang.Class<T>)
directly with FileIO.write()
or FileIO.writeDynamic()
.
public static <T> XmlIO.Sink<T> sink(java.lang.Class<T> recordClass)
The produced file consists of a single root element containing 1 sub-element per element written to the sink.
The given 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.
For example, consider the following class with JAXB annotations:
@XmlRootElement(name = "word_count_result") @XmlType(propOrder = {"word", "frequency"}) public class WordFrequency { public String word; public long frequency; }
The following will produce XML output with a root element named "words" from a PCollection of WordFrequency objects:
p.apply(FileIO.<WordFrequency>write()
.via(XmlIO.sink(WordFrequency.class).withRootElement("words"))
.to(prefixAndShardTemplate("...", DEFAULT_UNWINDOWED_SHARD_TEMPLATE + ".xml"));
The output 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>