{"id":42673,"date":"2016-12-26T11:00:35","date_gmt":"2016-12-26T09:00:35","guid":{"rendered":"http:\/\/examples.javacodegeeks.com\/?p=42673"},"modified":"2016-12-24T19:39:20","modified_gmt":"2016-12-24T17:39:20","slug":"java-xpath-examples","status":"publish","type":"post","link":"https:\/\/examples.javacodegeeks.com\/java-development\/core-java\/xml\/xpath\/java-xpath-examples\/","title":{"rendered":"Java XPath Examples"},"content":{"rendered":"

1. Introduction<\/h2>\n

The previous article, Java XPath Best Practices Tutorial (https:\/\/examples.javacodegeeks.com\/core-java\/xpath-best-practices-tutorial\/<\/a>), explored how to set up a Java application to create a DOM (Document Object Model) document using a DOM parser to read an XML file; and an XPath object to evaluate XPath expressions as applied to the DOM.<\/p>\n

This article dives into how to construct XPath expressions. Starting with the syntax used to build XPath expressions, and ending with some examples sum up the concepts explored.<\/p>\n

The download for this article includes both the inventory.xml file used in the previous article and also includes the complete source code for a simple Java console application, called XPath Expression Explorer. More details about XPath Expression Explorer revealed throughout this article.<\/p>\n

2. XPath Expression Explorer<\/h2>\n

This article builds and uses a Java application (XPath Expression Explorer) to reveal facts about XPath expressions and to help shorten the learning curve encountered when learning XPath expressions.<\/p>\n

2.1 The Data<\/h3>\n

Below is the inventory.xml file from the previous article.<\/p>\n

inventory.xml<\/em><\/span><\/p>\n

<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n<inventory>\r\n    <vendor name=\"Dell\">\r\n        <computer>\r\n            <model>Win 10 Laptop<\/model>\r\n            <os>Windows 10<\/os>\r\n            <cpu>Intel i7<\/cpu>\r\n            <ram>12GB<\/ram>\r\n            <price>900.00<\/price>\r\n        <\/computer>\r\n        <computer>\r\n            <model>Low Cost Windows Laptop<\/model>\r\n            <os>Windows 10 Home<\/os>\r\n            <cpu>Intel Pentium<\/cpu>\r\n            <ram>4GB<\/ram>\r\n            <price>313.00<\/price>\r\n        <\/computer>\r\n        <computer>\r\n            <model>64 Bit Windows Desktop Computer<\/model>\r\n            <os>Windows 10 Home 64 Bit<\/os>\r\n            <cpu>AMD A8-Series<\/cpu>\r\n            <ram>8GB<\/ram>\r\n            <price>330.00<\/price>\r\n        <\/computer>\r\n    <\/vendor>\r\n    <vendor name=\"Apple\">\r\n        <computer>\r\n            <model>Apple Desktop Computer<\/model>\r\n            <os>MAC OS X<\/os>\r\n            <cpu>Intel Core i5<\/cpu>\r\n            <ram>8GB<\/ram>\r\n            <price>1300.00<\/price>\r\n        <\/computer>\r\n        <computer>\r\n            <model>Apple Low Cost Desktop Computer<\/model>\r\n            <os>OS X Yosemite<\/os>\r\n            <cpu>4th Gen Intel Core i5<\/cpu>\r\n            <ram>8GB<\/ram>\r\n            <price>700.00<\/price>\r\n        <\/computer>\r\n    <\/vendor>\r\n    <vendor name=\"HP\">\r\n        <computer>\r\n            <model>HP Low Cost Windows 10 Laptop<\/model>\r\n            <os>Windows 10 Home<\/os>\r\n            <cpu>AMD A6-Series<\/cpu>\r\n            <ram>4GB<\/ram>\r\n            <price>230.00<\/price>\r\n        <\/computer>\r\n        <computer>\r\n            <model>Windows 7 Desktop<\/model>\r\n            <os>Windows 7<\/os>\r\n            <cpu>6th Gen Intel Core i5<\/cpu>\r\n            <ram>6GB<\/ram>\r\n            <price>750.00<\/price>\r\n        <\/computer>\r\n        <computer>\r\n            <model>HP High End, Low Cost 64 Bit Desktop<\/model>\r\n            <os>Windows 10 Home 64 Bit<\/os>\r\n            <cpu>6th Gen Intel Core i7<\/cpu>\r\n            <ram>12GB<\/ram>\r\n            <price>800.00<\/price>\r\n        <\/computer>\r\n    <\/vendor>\r\n<\/inventory>\r\n\r\nA.   There are 3 vendors; each vendor has a unique name\r\nB.   There are 8 computers defined\r\nC.   Each computer node has 5 children: \r\n     * model \u2013 Name of this configuration\r\n     * os \u2013 Name of Operating System installed\r\n     * cpu \u2013 Type of processor\r\n     * ram \u2013 size of installed RAM\r\n     * price \u2013 expressed as a decimal number\r\n<\/pre>\n
2.2 The Application<\/h3>\n
Below is the Java code that comprises the XPath Expression Explorer console application.<\/p>\n
JavaXPathExpressionExplorer.java<\/em><\/span><\/p>\n
import java.io.BufferedReader;\r\nimport java.io.IOException;\r\nimport java.io.InputStreamReader;\r\nimport javax.xml.parsers.DocumentBuilder;\r\nimport javax.xml.parsers.DocumentBuilderFactory;\r\nimport javax.xml.parsers.ParserConfigurationException;\r\nimport javax.xml.xpath.XPath;\r\nimport javax.xml.xpath.XPathConstants;\r\nimport javax.xml.xpath.XPathExpressionException;\r\nimport javax.xml.xpath.XPathFactory;\r\n\r\nimport org.w3c.dom.Document;\r\nimport org.w3c.dom.Node;\r\nimport org.w3c.dom.NodeList;\r\n\r\nimport org.xml.sax.SAXException;\r\n\r\npublic class JavaXPathExpressionExplorer {\r\n\r\n    public static final String DEFAULT_XML_FILENAME = \"inventory.xml\";\r\n\r\n    public static void main(String... args) {\r\n\r\n        \/\/ Setup an InputStreamReader to read from the keyboard\r\n        InputStreamReader reader = new InputStreamReader(System.in);\r\n        BufferedReader in = new BufferedReader(reader);\r\n\r\n        \/\/ Instantiate the factory that supplies the DOM parser\r\n        DocumentBuilderFactory builderFactory =\r\n                DocumentBuilderFactory.newInstance();\r\n\r\n        DocumentBuilder domParser = null;\r\n        try {\r\n            \/\/ Instantiate the DOM parser\r\n            domParser = builderFactory.newDocumentBuilder();\r\n\r\n            \/\/ Load the DOM Document from the XML data using the parser\r\n            Document domDocument =\r\n                    domParser.parse(getFileInputStreamName(in));\r\n\r\n            \/\/ Instantiate an XPath object which compiles\r\n            \/\/ and evaluates XPath expressions.\r\n            XPath xPath = XPathFactory.newInstance().newXPath();\r\n\r\n            while (true) {\r\n\r\n                System.out.print(\"Enter expression (blank line to exit): \");\r\n                String expr = in.readLine(); \/\/ Holds the XPath expression\r\n\r\n                try {\r\n                    if ((expr == null) || (expr.length() == 0)) {\r\n                        System.exit(0); \/\/ User is done entering expressions\r\n                    }\r\n                    System.out.println(expr + \" evaluates to:\");\r\n\r\n                    \/\/ See if expr evaluates to a String\r\n                    String resString = (String) xPath.compile(expr).\r\n                        evaluate(domDocument, XPathConstants.STRING);\r\n                    if (resString != null) {\r\n                        System.out.println(\"String: \" + resString);\r\n                    }\r\n\r\n                    Number resNumber = (Number) xPath.compile(expr).\r\n                        evaluate(domDocument, XPathConstants.NUMBER);\r\n                    if (resNumber != null) {\r\n                        System.out.println(\"Number: \" + resNumber);\r\n                    }\r\n\r\n                    Boolean resBoolean = (Boolean) xPath.compile(expr).\r\n                        evaluate(domDocument, XPathConstants.BOOLEAN);\r\n                    if (resNumber != null) {\r\n                        System.out.println(\"Boolean: \" + resBoolean);\r\n                    }\r\n\r\n                    Node resNode = (Node) xPath.compile(expr).\r\n                        evaluate(domDocument, XPathConstants.NODE);\r\n                    if (resNode != null) {\r\n                        System.out.println(\"Node: \" + resNode);\r\n                    }\r\n\r\n                    NodeList resNodeList = (NodeList) xPath.compile(expr).\r\n                        evaluate(domDocument, XPathConstants.NODESET);\r\n                    if (resNodeList != null) {\r\n                        int lenList = resNodeList.getLength();\r\n                        System.out.println(\"Number of nodes in NodeList: \" + lenList);\r\n                        for (int i = 1; i <= lenList; i++) {\r\n                            resNode = resNodeList.item(i-1);\r\n                            String resNodeNameStr = resNode.getNodeName();\r\n                            String resNodeTextStr = resNode.getTextContent();\r\n                            System.out.println(i + \": \" + resNode + \"  (NodeName:'\" +\r\n                                resNodeNameStr + \"'    NodeTextContent:'\" + \r\n                                resNodeTextStr + \"')\");\r\n                        }\r\n                    }\r\n                    outputSeparator();\r\n\r\n                } catch (XPathExpressionException e) {\r\n                    \/\/ Do nothing. This prevents output to console if \r\n                    \/\/ expression result type is not appropriate\r\n                    \/\/ for the XPath expression being compiled and evaluated\r\n                }\r\n\r\n            } \/\/ end  while (true)\r\n\r\n        } catch (SAXException e) {\r\n            \/\/ Even though we are using a DOM parser a SAXException is thrown\r\n            \/\/ if the DocumentBuilder cannot parse the XML file\r\n            e.printStackTrace();\r\n        } catch (IOException e) {\r\n            e.printStackTrace();\r\n        } catch (ParserConfigurationException e){\r\n                e.printStackTrace();\r\n        }\r\n    }\r\n\r\n    \/\/ Helper method to load the XML file into the DOM Document\r\n    public static String getFileInputStreamName(BufferedReader inputReader) {\r\n        System.out.print(\"Enter XML file name (abc.xml) \u201c+ \r\n            \u201cor leave blank to use \"+DEFAULT_XML_FILENAME+\": \");\r\n        String fileName = null;\r\n        try {\r\n            fileName = inputReader.readLine();\r\n        } catch (IOException e) {\r\n            e.printStackTrace();\r\n        }\r\n        if ((fileName == null) || (fileName.length() == 0)) {\r\n            return DEFAULT_XML_FILENAME;\r\n        }\r\n        return fileName;\r\n    }\r\n\r\n    \/\/ Helper method to pretty up the output\r\n    public static void outputSeparator() {\r\n        System.out.println(\"=+=+=+=+=+=+=+=+\");\r\n    }\r\n\r\n}\r\n<\/pre>\n
The application initially prompts the user for an XML filename. Respond to this prompt with a blank line to use the inventory.xml file found in the application\u2019s classpath.
 
<\/div> <\/div><\/p>\n
The application then takes an XPath expression entered from the keyboard, compiles, and evaluates the expression using different return types (as determined by XPathConstants) and displays the results to the user.<\/p>\n
The main loop in this application repeatedly prompts for XPath expressions. Entering a blank line terminates the application.<\/p>\n
Admittedly the application is crude, but it is effective for learning about XPath expressions.<\/p>\n
3. XPath Expressions<\/h2>\n
3.1 XPathConstants Effect on XPath Expressions<\/h3>\n
The evaluate() method of an XPath object allows the user to specify an optional XPathConstant which determines the data type of the result returned, which changes the value of the result.<\/p>\n
NOTE: If the optional XPathConstant is not passed to evaluate(), the data type of the result returned by evaluate() is String.<\/p>\n
The table below shows the effects of the different XPathConstants when the XPath expression \/inventory\/vendor\/computer\/cpu[text() = “Intel Pentium”] is evaluated given a DOM built from the inventory.xml file (noted in section 2.1 The Data)<\/p>\n
Table showing effects of different XPathConstants<\/em><\/span><\/p>\n
XPath Constant          Java Data Type    Value Returned\r\n\r\nXPathConstant.String    String            Intel Pentium\r\nXPathConstant.Number    Number            NaN\r\nXPathConstant.Boolean   Boolean           true\r\nXPathConstant.Node      Node              [cpu: null]\r\nXPathConstant.NodeList  NodeList          [cpu: null]\r\n<\/pre>\n
It is worth noting: Using the NodeList on line 7:<\/p>\n