XML file input of Chapter 13 of kettle paoding jieniu

introduction

In the last article , We introduced ：CSV Various detailed settings of the file input component , The actual combat demonstrates how to operate it to read the data on the disk CSV file . Finally, it expanded , Use the text file input component to read... On disk CSV file .

In this article , Let's go on to introduce ：kettle Medium XML File input component (Get data from XML).

To learn to understand XML File input component , We're going to expand our conversation XML and XPath What happened .

XML Those things

a、 summary

Xml A markup language used to mark electronic documents to make them structured , Can be used to tag data 、 Define data types , Is a source language that allows users to define their own markup language .Xml It's a standard universal markup language (SGML) Subset , Very suitable Web transmission .XML Provides a unified way to describe and exchange structured data independent of the application or vendor .

In a word ：xml Itself is a format specification , Is a text format specification that includes data and data description .

b、 Illustrate with examples

I want to transmit a piece of data to each other , The content is " Big Feige , Data architect ,88 year ". Split this paragraph into three data according to attributes , nickname ： Big Feige , position ： Data architect , The year of birth ：88 year .

Programs are not like people , It can't literally , And automatically split the data . It needs human help to split the program , Therefore, there are various data formats and splitting methods .

(1)、 situation 1

The data is " Big Feige , Data architect ,88 year "

according to “,” Split , The first part is the nickname , The second part is the position , The third part is the age of birth .

(2)、 situation 2

The data is " Big Feige * Data architect *88 year "

according to “*” Split , The first part is the nickname , The second part is the position , The third part is the age of birth .

summary

Both methods can be used to hold data and can be parsed , But it's not intuitive , Versatility is not good , And if there is a string that exceeds the limited number of words, it can't hold , It is also possible that the data itself contains special characters , You also need to escape .

Based on this situation , There is xml This data format , The above data is used XML What they say , It will be much clearer .

(1)、xml How to write it 1

<person nickname=" Big Feige " title=" Data architect " birth="88 year "></person >

(2)、xml How to write it 2

<person>

  <nickname value=" Big Feige "></nickname>

  <title value=" Data architect "></title>

  <birth value="88 year "></birth>

</person>​

(3)、 Storage structure

A tree structure

xml Statement

xml Statements are generally xml The first line of the document ,xml The declaration consists of the following 2 Component composition ：version and encoding

Example ：<?xml version="1.0" encoding="UTF-8"?>

Root element

Whole XML In file , There is and only one root element . It is XML In file , The first is the beginning \ The last tag pair . In the following data ,person It's the root element .

<person>       ----------- In the beginning

  <nickname value=" Big Feige "></nickname>

  <title value=" Data architect "></title>

  <birth value="88 year "></birth>

</person>        --------- At the end of the day

Elements

grammar ：< The element tag > Content </ The element tag >

(1) be-all xml Every element must have an end tag ;

<title> Data architect </title>

(2)xml Tags are case sensitive ;

correct ：<title> Data architect </title>

error ：<Title> Data architect </title>

(3)xml You have to nest... Correctly ;

correct ：<title><birth> Data architect </birth></title>

error ：<title><birth> Data architect </title></birth>

(4) Naming rules for elements ：

The name can contain letters 、 Numbers or other characters ;

Names cannot begin with numbers or punctuation ;

The name cannot contain spaces .

(5) Empty elements

<nickname></nickname>

<title></title>

<birth></birth>

attribute

(1)、 grammar

< Element name Property name =" Property value "/>

Examples are as follows ：

<person>

 <nickname value=" Big Feige "/>

 <title value=" Data architect "/>

 <birth value="88 year "/>

</person>

(2)、 Be careful

Attribute values are wrapped in double quotation marks ; An element can have multiple attributes , Its basic format is ：

< Element name Property name =" Property value " Property name =" Property value ">

Property values cannot contain <.",&.

xml Parsing

Constant XML Analytical techniques include 3 Kind of ：SAX analysis XML、DOM analysis XML、Pull analysis XML

A comparison of technologies

Memory footprint ：SAX、Pull Than DOM It is better to ;

programmatically ：SAX Use event driven , When the corresponding event is triggered , Will call the method prepared by the user , That is to say, every kind of XML, It is necessary to write a new one suitable for this class XML The processing of the class .DOM yes W3C The specification of ,Pull concise .

Access and modify ：SAX Flow analysis is adopted ,DOM Random access .

access ：SAX,Pull The parsing method is synchronous ,DOM Word for word

XPath expression

XPath( Full name ：XML Path Language) namely XML Path to the language , It's a door in XML The language in which information is found in a document , Originally used to search XML file , At the same time, it is also suitable for searching HTML file .

Multiple types of nodes

XPath Various types of nodes are provided , Common nodes are ： Elements 、 attribute 、 Text 、 Comments and document nodes . As shown below ：

<?xml version="1.0" encoding="utf-8"?>

<website>

<site>

 <title lang="zh-CN">website name</title>

 <name> Programming help </name>

 <year>2010</year>

 <address>www.biancheng.net</address>

</site>

</website>

above XML Examples of nodes in the document ：

<website></website> ( Document nodes )

<name></name> ( Element nodes )

lang="zh-CN" ( Attribute node ) 

Node relationship

XML The node relationship and HTML Document similarity , There is also a father 、 Son 、 The same generation 、 Forefathers 、 Next generation nodes . As shown below ：

<?xml version="1.0" encoding="utf-8"?>

<website>

<site>

 <title lang="zh-CN">website name</title>

 <name> Programming help </name>

 <year>2010</year>

 <address>www.biancheng.net</address>

</site>

</website>

After the analysis of the above example , We will get the following results ：

title name year address All are site Child nodes of

site yes title name year address   Parent node

title name year address   Nodes of the same generation

title The ancestor node of the element is site website

website The descendant node of is site title name year address

Basic grammar uses

Xpath Use path expressions to select nodes in the document , The following table lists the common expression rules

xpath wildcard

Xpath The wildcard of the expression can be used to select unknown node elements , The basic grammar is as follows

Xpath Built-in functions

Xpath Provide 100 Multiple built-in functions , These functions provide us with a lot of convenience , For example, to achieve text matching 、 Fuzzy matching 、 And location matching , Here are some common built-in functions .

transformation

transformation (transaformation) yes ETL The main part of the solution , It handles extraction 、 transformation 、 Loading various operations on data lines .

Create transformations

What we have to do ETL operation , It's all designed in transformation , So we need to create a transformation first .

Save conversion

Give you a new conversion , Name it , And save

XML File input

This component can realize , From the specified XML File input data .

a、 The file specified

1、 The file label specifies the data source file , Click on “ Browse ” Button , Browse local xml file . Click on " increase " Button , You can add a file to " Select File " in , As shown below ：

The option configuration in this part is similar to that of the text file input component , No more detailed explanation .

b、 Content

Option description

c、 Field

Option description

d、 Other output fields

Option description

Okay , About XML Each tab of the file input component , I explained as much as I could . In fact, in my daily work , Not used so much , There are a few commonly used . But in the process of our study , I'd better speak more fully , I hope you spend time studying , Try to have a general understanding . Let's take an example to operate , This is a better way to absorb and understand .

Actual demonstration

a、 establish xml file

I am here D Under the plate , Create a xml file , Name it bigdata. The details are as follows

b、 Create transformations

c、XML File input settings

Add local xml file , As a data source

Set content and coding

Set fields ( Here you can refer to XPth expression )

d、 Preview the record

brothers , See the interface for previewing data , Prove that you have successfully passed XML File input component , Put one on your disk xml file , Read in . Congratulations , You already know how to use XML File input component .

Conclusion

This article mainly explains ：XML and XPath Those things , Then I explained XML Various detailed settings of the file input component , Finally, the actual combat demonstrates how to operate it to read the data on the disk xml file .

brothers , In fact, there is a distance between thinking and acting , If you think about it, it's gone , But you're doing it , It landed .

Don't say anything , Brothers, follow me and it's over , We still break up the way of kneading to say . The following content is more wonderful , Coming soon , Thank you for your attention ！！