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This article mainly shows you the "sample Analysis of XPATH Grammar in XML", which is easy to understand and clear. I hope it can help you solve your doubts. Let me lead you to study and learn "sample Analysis of XPATH Grammar in XML".

Why do I need xpath?

When using dom4j, we can't get an element across layers, we have to get it layer by layer, which is very troublesome.

So in order to make it easier for us to access a node, we can use xpath technology, which makes it very easy for us to read to the specified node.

Xpath is usually used in conjunction with dom4j, and if you want to use xpath, you need to introduce a new package Jaxen-1.1-beta-6.jar

The basic syntax of xpath is as follows:

1. The basic xpath syntax is similar to locating a file in a file system. If the path begins with a slash /, then the path represents the absolute path to an element.

(1) / AAA, which indicates that the root element AAA is selected

Here, here.

(2) / AAA/CCC, which indicates that all CCC child elements of AAA are selected

Here, here.

(3) / AAA/DDD/BBB, which indicates that all BBB child elements of DDD, a child element of AAA, are selected

Here

So how do you use xpath in dom4j? It's actually very simple:

/ / 1. Get the SAXReader parser SAXReader saxReader = new SAXReader (); / / 2. Specify which file to parse Document document = saxReader.read (new File (path)); / / 3. You can use xpath read / / document.selectNodes (args) to return multiple elements / / document.selectSingleNode (args) to return a single element List nodes = document.selectNodes ("/ AAA/BBB")

After you get the document object through dom4j, you can use document's selectNodes (args) method, which returns a List based on the xpath path you write, and the rest is similar to dom4j.

It also has a selectSingleNode (args) method that returns a single Node.

Let's move on to other xpath syntax:

two。 If the path begins with a double slash / /, it represents all elements in the document that meet the rules after the double slash / / (regardless of hierarchy)

(1) / / BBB, which indicates that all BBB elements are selected

Here.

(2) / / DDD/BBB, indicating that all parent elements are BBB elements of DDD

Here.

3. An asterisk * indicates that all elements located by the path before the asterisk are selected

(1) / AAA/CCC/DDD/*, it means to select all elements whose paths are attached to / AAA/CCC/DDD:

Here, here.

(2) / * / BBB, which represents all BBB elements with three ancestral elements

Here.

(3) / / *, which indicates that all elements are selected

4. The expression in square brackets can further specify the element, where the number represents the position of the element in the selection set, and the last () function represents the last element in the selection set. It is important to note that the subscript here starts with 1, not 0!

(1) / AAA/BBB [1], which represents the selection of the first BBB child element of AAA

This

(2) / AAA/BBB [last ()], indicating that the last BBB element of the AAA is selected

This

5. Operations on attributes

(1) / / @ id, select all id attributes. Note: return all id attributes as nodes, not nodes with id attributes.

The id attribute node returned here also returns the id attribute node here.

(2) / / BBB [@ id], select all BBB nodes with id attribute

Return this BBB node also return this BBB node

(3) / / BBB [@ name], select all BBB nodes with name attribute

Return to this BBB node

(4) / / BBB [@ *], select all BBB nodes with attributes

Return to this BBB node return to this BBB node return to this BBB node

(5) / / BBB [not (@ *)], select all BBB nodes without attributes

This

6. The value of the attribute can be used as a criterion for selection

(1) / / BBB [@ id='b1'], select the BBB element that contains the attribute id and whose value is' b1'

This

The 7.count () function can count the number of selected elements

(1) / / * [count (BBB) = 2], select the element that contains 2 BBB child elements

Return this element

(2) / / * [count (*) = 2], select the element with 2 child elements

Return this element also return this element

There are many other grammars, including the application of many functions, which are not used much, and will not be introduced here.

In addition, the syntax described above can be combined at will, such as the following xml document:

K1 K2 this

If we are now looking for the KKK child element of the 2CCC child element under the first BBB child element under the AAA element, the xpath path should say:

/ AAA/BBB [1] / CCC [2] / KKK

Why do I need xpath?

When using dom4j, we can't get an element across layers, we have to get it layer by layer, which is very troublesome.

So in order to make it easier for us to access a node, we can use xpath technology, which makes it very easy for us to read to the specified node.

Xpath is usually used in conjunction with dom4j, and if you want to use xpath, you need to introduce a new package Jaxen-1.1-beta-6.jar

The basic syntax of xpath is as follows:

1. The basic xpath syntax is similar to locating a file in a file system. If the path begins with a slash /, then the path represents the absolute path to an element.

(1) / AAA, which indicates that the root element AAA is selected

Here, here.

(2) / AAA/CCC, which indicates that all CCC child elements of AAA are selected

Here, here.

(3) / AAA/DDD/BBB, which indicates that all BBB child elements of DDD, a child element of AAA, are selected

Here

So how do you use xpath in dom4j? It's actually very simple:

/ / 1. Get the SAXReader parser SAXReader saxReader = new SAXReader (); / / 2. Specify which file to parse Document document = saxReader.read (new File (path)); / / 3. You can use xpath read / / document.selectNodes (args) to return multiple elements / / document.selectSingleNode (args) to return a single element List nodes = document.selectNodes ("/ AAA/BBB")

After you get the document object through dom4j, you can use document's selectNodes (args) method, which returns a List based on the xpath path you write, and the rest is similar to dom4j.

It also has a selectSingleNode (args) method that returns a single Node.

Let's move on to other xpath syntax:

two。 If the path begins with a double slash / /, it represents all elements in the document that meet the rules after the double slash / / (regardless of hierarchy)

(1) / / BBB, which indicates that all BBB elements are selected

Here.

(2) / / DDD/BBB, indicating that all parent elements are BBB elements of DDD

Here.

3. An asterisk * indicates that all elements located by the path before the asterisk are selected

(1) / AAA/CCC/DDD/*, it means to select all elements whose paths are attached to / AAA/CCC/DDD:

Here, here.

(2) / * / BBB, which represents all BBB elements with three ancestral elements

Here.

(3) / / *, which indicates that all elements are selected

4. The expression in square brackets can further specify the element, where the number represents the position of the element in the selection set, and the last () function represents the last element in the selection set. It is important to note that the subscript here starts with 1, not 0!

(1) / AAA/BBB [1], which represents the selection of the first BBB child element of AAA

This

(2) / AAA/BBB [last ()], indicating that the last BBB element of the AAA is selected

This

5. Operations on attributes

(1) / / @ id, select all id attributes. Note: return all id attributes as nodes, not nodes with id attributes.

The id attribute node returned here also returns the id attribute node here.

(2) / / BBB [@ id], select all BBB nodes with id attribute

Return this BBB node also return this BBB node

(3) / / BBB [@ name], select all BBB nodes with name attribute

Return to this BBB node

(4) / / BBB [@ *], select all BBB nodes with attributes

Return to this BBB node return to this BBB node return to this BBB node

(5) / / BBB [not (@ *)], select all BBB nodes without attributes

This

6. The value of the attribute can be used as a criterion for selection

(1) / / BBB [@ id='b1'], select the BBB element that contains the attribute id and whose value is' b1'

This

The 7.count () function can count the number of selected elements

(1) / / * [count (BBB) = 2], select the element that contains 2 BBB child elements

Return this element

(2) / / * [count (*) = 2], select the element with 2 child elements

Return this element also return this element

There are many other grammars, including the application of many functions, which are not used much, and will not be introduced here.

In addition, the syntax described above can be combined at will, such as the following xml document:

K1 K2 this

If we are now looking for the KKK child element of the 2CCC child element under the first BBB child element under the AAA element, the xpath path should say:

/ AAA/BBB [1] / CCC [2] / KKK

The above is all the content of the article "sample Analysis of XPATH Grammar in XML". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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