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How do I do XML String Parsing in Hive?

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How do I do XML String Parsing in Hive?

New Contributor

I Have an HBase table, which has the Row Key and CF:CQ that holds the base64 encoded xml

I created a Hive table using the HBase Handler with two columns rowdy and xml_string.

Now I created a view in Hive with rowkey and unbase64(xml_string). The xml_string is nested structure.

Now I need to extract attributes from xml_string along with the rowkey reference. Can someone help me with that. All I am seeing are the examples of reading xml files using HiveXMLSerde [com.ibm.spss.hive.serde2.xml.XmlSerDe] none for parsing an existing XML string inside a hive table / view.

5 REPLIES 5
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Re: How do I do XML String Parsing in Hive?

Super Guru

@Harish Cherukuri Good new you have several options. If you want to parse the data as it is fetched from the hbaseSerde, I would use hive XPathUDF.

Information about the UDF (from the link I provided):

xpath, xpath_short, xpath_int, xpath_long, xpath_float, xpath_double, xpath_number, xpath_string

  • Functions for parsing XML data using XPath expressions.
  • Since version: 0.6.0

    Overview

The xpath family of UDFs are wrappers around the Java XPath library javax.xml.xpath provided by the JDK. The library is based on the XPath 1.0 specification. Please refer tohttp://java.sun.com/javase/6/docs/api/javax/xml/xpath/package-summary.html for detailed information on the Java XPath library.

All functions follow the form: xpath_*(xml_string, xpath_expression_string). The XPath expression string is compiled and cached. It is reused if the expression in the next input row matches the previous. Otherwise, it is recompiled. So, the xml string is always parsed for every input row, but the xpath expression is precompiled and reused for the vast majority of use cases.

Backward axes are supported. For example:

> select xpath ('<a><b id="1"><c/></b><b id="2"><c/></b></a>','/descendant::c/ancestor::b/@id') from t1 limit 1 ; [1","2]

Each function returns a specific Hive type given the XPath expression:

  • xpath returns a Hive array of strings.
  • xpath_string returns a string.
  • xpath_boolean returns a boolean.
  • xpath_short returns a short integer.
  • xpath_int returns an integer.
  • xpath_long returns a long integer.
  • xpath_float returns a floating point number.
  • xpath_double,xpath_number returns a double-precision floating point number (xpath_number is an alias forxpath_double).

The UDFs are schema agnostic - no XML validation is performed. However, malformed xml (e.g., <a><b>1</b></aa>) will result in a runtime exception being thrown.

Following are specifics on each xpath UDF variant.

xpath

The xpath() function always returns a hive array of strings. If the expression results in a non-text value (e.g., another xml node) the function will return an empty array. There are 2 primary uses for this function: to get a list of node text values or to get a list of attribute values.

Examples:

Non-matching XPath expression:

> select xpath('<a><b>b1</b><b>b2</b></a>','a/*') from src limit 1 ; []

Get a list of node text values:

> select xpath('<a><b>b1</b><b>b2</b></a>','a/*/text()') from src limit 1 ; [b1","b2]

Get a list of values for attribute 'id':

> select xpath('<a><b id="foo">b1</b><b id="bar">b2</b></a>','//@id') from src limit 1 ; [foo","bar]

Get a list of node texts for nodes where the 'class' attribute equals 'bb':

> SELECT xpath ('<a><b>b1</b><b>b2</b><b>b3</b><c>c1</c><c>c2</c></a>', 'a/*[@class="bb"]/text()') FROM src LIMIT 1 ; [b1","c1]

xpath_string

The xpath_string() function returns the text of the first matching node.

Get the text for node 'a/b':

> SELECT xpath_string ('<a><b>bb</b><c>cc</c></a>', 'a/b') FROM src LIMIT 1 ; bb

Get the text for node 'a'. Because 'a' has children nodes with text, the result is a composite of text from the children.

> SELECT xpath_string ('<a><b>bb</b><c>cc</c></a>', 'a') FROM src LIMIT 1 ; bbcc

Non-matching expression returns an empty string:

> SELECT xpath_string ('<a><b>bb</b><c>cc</c></a>', 'a/d') FROM src LIMIT 1 ;

Gets the text of the first node that matches '//b':

> SELECT xpath_string ('<a><b>b1</b><b>b2</b></a>', '//b') FROM src LIMIT 1 ; b1

Gets the second matching node:

> SELECT xpath_string ('<a><b>b1</b><b>b2</b></a>', 'a/b[2]') FROM src LIMIT 1 ; b2

Gets the text from the first node that has an attribute 'id' with value 'b_2':

> SELECT xpath_string ('<a><b>b1</b><b id="b_2">b2</b></a>', 'a/b[@id="b_2"]') FROM src LIMIT 1 ; b2

xpath_boolean

Returns true if the XPath expression evaluates to true, or if a matching node is found.

Match found:

> SELECT xpath_boolean ('<a><b>b</b></a>', 'a/b') FROM src LIMIT 1 ; true

No match found:

> SELECT xpath_boolean ('<a><b>b</b></a>', 'a/c') FROM src LIMIT 1 ; false

Match found:

> SELECT xpath_boolean ('<a><b>b</b></a>', 'a/b = "b"') FROM src LIMIT 1 ; true

No match found:

> SELECT xpath_boolean ('<a><b>10</b></a>', 'a/b < 10') FROM src LIMIT 1 ; false

xpath_short, xpath_int, xpath_long

These functions return an integer numeric value, or the value zero if no match is found, or a match is found but the value is non-numeric. Mathematical operations are supported. In cases where the value overflows the return type, then the maximum value for the type is returned.

No match:

> SELECT xpath_int ('<a>b</a>', 'a = 10') FROM src LIMIT 1 ; 0

Non-numeric match:

> SELECT xpath_int ('<a>this is not a number</a>', 'a') FROM src LIMIT 1 ; 0 > SELECT xpath_int ('<a>this 2 is not a number</a>', 'a') FROM src LIMIT 1 ; 0

Adding values:

> SELECT xpath_int ('<a><b>1</b><b>2</b><b>4</b><c>8</c></a>', 'sum(a/*)') FROM src LIMIT 1 ; 15 > SELECT xpath_int ('<a><b>1</b><b>2</b><b>4</b><c>8</c></a>', 'sum(a/b)') FROM src LIMIT 1 ; 7 > SELECT xpath_int ('<a><b>1</b><b>2</b><b>4</b><c>8</c></a>', 'sum(a/b[@class="odd"])') FROM src LIMIT 1 ; 5

Overflow:

> SELECT xpath_int ('<a><b>2000000000</b><c>40000000000</c></a>', 'a/b * a/c') FROM src LIMIT 1 ; 2147483647

xpath_float, xpath_double, xpath_number

Similar to xpath_short, xpath_int and xpath_long but with floating point semantics. Non-matches result in zero. However, non-numeric matches result in NaN. Note that xpath_number() is an alias for xpath_double().

No match:

> SELECT xpath_double ('<a>b</a>', 'a = 10') FROM src LIMIT 1 ; 0.0

Non-numeric match:

> SELECT xpath_double ('<a>this is not a number</a>', 'a') FROM src LIMIT 1 ; NaN

A very large number:

SELECT xpath_double ('<a><b>2000000000</b><c>40000000000</c></a>', 'a/b * a/c') FROM src LIMIT 1 ; 8.0E19
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Re: How do I do XML String Parsing in Hive?

Super Guru

@Harish Cherukuri

Can you try this? It seems to work well with nested structures and output into lateral view.

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Re: How do I do XML String Parsing in Hive?

New Contributor

Thank You Sunile.

I have explored the same based on information available on apache.hive site.

My bad, I may not have provided the detail on what I am trying to do. The XML String I am trying to parse is a nested string and second part is I am trying to create multiple records based on number of times each node repeats with proper associations to child elements.

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Re: How do I do XML String Parsing in Hive?

New Contributor

I have a situation here, my xml is having multiple nodes with same tag hence I have used xpath(tags/tag/innertag/) and it is returning array of a string now I have to use the multiple explode function - which is creating problem as I'm getting Cartesian product values :( I should get

A a1

B b1

but I'm getting

A a1

A b1

B a1

B b1

This is the reason my hive table data increased unnecessary and also I'm not getting correct results. Any UDF of other approach which may help me please advice.

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Re: How do I do XML String Parsing in Hive?

New Contributor

ou can automate the whole process of generating ORC/Parquet for Hive in a relational structure. This blog post shows how to convert MISMO XML to Hive and Parquet