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How to extract specific blocks from xml in java?

I have the following xml file.

<?xml version="1.0" encoding="UTF-8"?> <databaseChangeLog> <changeSet author="debdipta.h (generated)" id="1442927616936-399"> <createTable tableName="SI_FORWARDING_EVENT_HISTORY_AU"> <column name="FORWARDING_ID_O" type="NUMBER" /> <column name="FORWARDING_ID_N" type="NUMBER" /> <column name="ASSIGNMENT_ID_O" type="NUMBER" /> <column name="ASSIGNMENT_ID_N" type="NUMBER" /> <column name="PROCESS_INSTANCE_ID_O" type="NUMBER" /> <column name="PROCESS_INSTANCE_ID_N" type="NUMBER" /> <column name="ORIGINAL_USER_ID_O" type="NUMBER" /> <column name="ORIGINAL_USER_ID_N" type="NUMBER" /> <column name="FORWARD_FROM_USER_O" type="NUMBER" /> <column name="FORWARD_FROM_USER_N" type="NUMBER" /> <column name="FORWARD_TO_USER_O" type="NUMBER" /> <column name="FORWARD_TO_USER_N" type="NUMBER" /> <column name="COMMENTS_O" type="VARCHAR2(4000 CHAR)" /> <column name="COMMENTS_N" type="VARCHAR2(4000 CHAR)" /> <column name="XML_O" type="VARCHAR2(4000 CHAR)" /> <column name="XML_N" type="VARCHAR2(4000 CHAR)" /> <column name="CREATED_BY_O" type="NUMBER" /> <column name="CREATED_BY_N" type="NUMBER" /> <column name="CREATION_DATE_O" type="date" /> <column name="CREATION_DATE_N" type="date" /> <column name="AUDIT_TRAIL_REASON" type="VARCHAR2(1000 CHAR)" /> <column name="TRANSACTION_TYPE" type="VARCHAR2(100 CHAR)" /> </createTable> </changeSet> <changeSet author="deb.h" id="4588999797"> <createView /> </changeSet> <changeSet author="deb.h" id="4588999797"> <createTable /> </changeSet> <changeSet author="deb.h" id="4588999797"> <createView /> </changeSet> </databaseChangeLog>

I want to extract blocks only with createTable, which will be extracted to another xml file using xpath. The result should look like this:

 <databaseChangeLog> <changeSet author="debdipta.h (generated)" id="1442927616936-399"> <createTable tableName="SI_FORWARDING_EVENT_HISTORY_AU"> <column name="FORWARDING_ID_O" type="NUMBER"/> <column name="FORWARDING_ID_N" type="NUMBER"/> <column name="ASSIGNMENT_ID_O" type="NUMBER"/> <column name="ASSIGNMENT_ID_N" type="NUMBER"/> <column name="PROCESS_INSTANCE_ID_O" type="NUMBER"/> <column name="PROCESS_INSTANCE_ID_N" type="NUMBER"/> <column name="ORIGINAL_USER_ID_O" type="NUMBER"/> <column name="ORIGINAL_USER_ID_N" type="NUMBER"/> <column name="FORWARD_FROM_USER_O" type="NUMBER"/> <column name="FORWARD_FROM_USER_N" type="NUMBER"/> <column name="FORWARD_TO_USER_O" type="NUMBER"/> <column name="FORWARD_TO_USER_N" type="NUMBER"/> <column name="COMMENTS_O" type="VARCHAR2(4000 CHAR)"/> <column name="COMMENTS_N" type="VARCHAR2(4000 CHAR)"/> <column name="XML_O" type="VARCHAR2(4000 CHAR)"/> <column name="XML_N" type="VARCHAR2(4000 CHAR)"/> <column name="CREATED_BY_O" type="NUMBER"/> <column name="CREATED_BY_N" type="NUMBER"/> <column name="CREATION_DATE_O" type="date"/> <column name="CREATION_DATE_N" type="date"/> <column name="AUDIT_TRAIL_REASON" type="VARCHAR2(1000 CHAR)"/> <column name="TRANSACTION_TYPE" type="VARCHAR2(100 CHAR)"/> </createTable> </changeSet> <changeSet author="deb.h" id="4588999797"> <createTable></createTable> </changeSet> </databaseChangeLog>

The code I have done now looks like this:

 public class extractXML { public static void main(String[] args)throws Exception{ //String test=readXMLasString.convert("E:\\db.borilog.xml"); DocumentBuilderFactory dbf=DocumentBuilderFactory.newInstance(); DocumentBuilder db=dbf.newDocumentBuilder(); Document doc=db.parse(new FileInputStream("E:\\db.borilog.xml")); XPath xpath=XPathFactory.newInstance().newXPath(); Node res=(Node) xpath.evaluate("databaseChangeLog/changeSet",doc,XPathConstants.NODE); System.out.println(NodeToString(res)); } public static String NodeToString(Node node)throws TransformerException{ StringWriter buf=new StringWriter(); Transformer xform=TransformerFactory.newInstance().newTransformer(); xform.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes"); xform.transform(new DOMSource(node),new StreamResult(buf)); return(buf.toString()); } }

I do not understand how to iterate over xpath and extract the necessary blocks.

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2 answers

You need to use NodeList :

 NodeList nodeList = (NodeList)xpath.evaluate("//changeSet[createTable]",doc,XPathConstants.NODE); String[] results = new String[nodeList.getLength()]; for (int index = 0; index < nodeList.getLength(); index++) { Node node = nodeList.item(index); String nodeAsString = NodeToString(node); results[index] = nodeAsString; }
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This will block all createTable blocks.

 //changeSet[createTable]

or

 /databaseChangeLog/changeSet[createTable]

Here you are requesting the return of changeSet blocks where createTable exists.

Result

 <changeSet author="debdipta.h (generated)" id="1442927616936-399"> <createTable tableName="SI_FORWARDING_EVENT_HISTORY_AU"> <column name="FORWARDING_ID_O" type="NUMBER" /> <column name="FORWARDING_ID_N" type="NUMBER" /> <column name="ASSIGNMENT_ID_O" type="NUMBER" /> <column name="ASSIGNMENT_ID_N" type="NUMBER" /> <column name="PROCESS_INSTANCE_ID_O" type="NUMBER" /> <column name="PROCESS_INSTANCE_ID_N" type="NUMBER" /> <column name="ORIGINAL_USER_ID_O" type="NUMBER" /> <column name="ORIGINAL_USER_ID_N" type="NUMBER" /> <column name="FORWARD_FROM_USER_O" type="NUMBER" /> <column name="FORWARD_FROM_USER_N" type="NUMBER" /> <column name="FORWARD_TO_USER_O" type="NUMBER" /> <column name="FORWARD_TO_USER_N" type="NUMBER" /> <column name="COMMENTS_O" type="VARCHAR2(4000 CHAR)" /> <column name="COMMENTS_N" type="VARCHAR2(4000 CHAR)" /> <column name="XML_O" type="VARCHAR2(4000 CHAR)" /> <column name="XML_N" type="VARCHAR2(4000 CHAR)" /> <column name="CREATED_BY_O" type="NUMBER" /> <column name="CREATED_BY_N" type="NUMBER" /> <column name="CREATION_DATE_O" type="date" /> <column name="CREATION_DATE_N" type="date" /> <column name="AUDIT_TRAIL_REASON" type="VARCHAR2(1000 CHAR)" /> <column name="TRANSACTION_TYPE" type="VARCHAR2(100 CHAR)" /> </createTable> </changeSet> <changeSet author="deb.h" id="4588999797"> <createTable /> </changeSet>
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Source: https://habr.com/ru/post/1234114/

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