[JAVA] Create your own dialect to convert line feed code to line feed tag in Thymeleaf3

Abstract

Even if Thymeleaf outputs a character string including a line feed code, it only breaks in the HTML source and does not break on the display. Create your own dialect with the function of converting the line feed code to a line feed tag and outputting a character string, and use it as an alternative dialect of th: text. Although the implementation is different between Thymeleaf 2 and 3, this paper deals with Thymeleaf3.

environment

• Java SE 8 (jdk-8u181)
• Maven 3.5.4
• Spring Boot 2.0.5
• Thymeleaf 3.0.9

Overview

• Implement the Proccessor class (the class that actually describes the operation)
• Implement the Dialect class (a class that collectively defines a Proccessor as a dialect)
• Set to Bean
• Used in templates

Detailed procedure

Implement the Proccessor class (the class that actually describes the operation)

Class definition

From the Proccessor type abstract classes provided by Thymeleaf, select the one that is close to what you want to do and create a class that inherits it. This time, we will create something similar to the Standard Dialect th: text, so we will inherit ʻAbstractStandardExpressionAttributeTagProcessor`.

public class BreakLineProccessor extends AbstractStandardExpressionAttributeTagProcessor {
  ...
}

constructor

Be sure to create a constructor and define how the Proccessor will be used.

  private static final String ATTR_NAME = "brtext";

  public BreakLineProccessor(String dialectPrefix, int precedence) {
    super(TemplateMode.HTML, dialectPrefix, ATTR_NAME, precedence, true);
  }

In addition, each argument of the constructor of ʻAbstractStandardExpressionAttributeTagProcessor` which is the inheritance source class is as follows.

This time, only the prefix and priority were received from outside, and the rest were fixed values.

Process execution method

Describe the process by overriding the abstract method doProcess. In the case of doProcess of ʻAbstractStandardExpressionAttributeTagProcessor, the result of interpreting the EL expression is stored in the argument ʻexpressionResult. The outline of the whole process is as follows.

1. Get the ʻIModelFactory instance from the argument context`.
2. Create a ʻIModel instance from the obtained ʻIModelFactory instance.
3. Add elements (character strings and tags) to be reflected in HTML to the created ʻIModel instance in order. The instance to be added is also created from the ʻIModelFactory instance.
4. Apply the ʻIModel instance to the argument structureHandler`.

  @Override
	protected void doProcess(ITemplateContext context, IProcessableElementTag tag, AttributeName attributeName,
			String attributeValue, Object expressionResult, IElementTagStructureHandler structureHandler) {
		//If null, nothing is output and processing ends
		if (expressionResult == null) return;

		IModelFactory factory = context.getModelFactory();
		IModel model = factory.createModel();

		ITemplateEvent brTag = factory.createOpenElementTag("br");

    //Split by line feed code
		String[] lines = expressionResult.toString().split("\r\n|\r|\n", -1);
		for (String line : lines) {
      // <br>+Add one line of string to model
			model.add(brTag);
			model.add(factory.createText(line));
		}
		//At the beginning<br>Remove tag
		model.remove(0);

		structureHandler.setBody(model, false);

Implement the Dialect class (a class that collectively defines a Proccessor as a dialect)

Class definition

Create a class that inherits (implements) the dialect processing created from the Dialect abstract class and interface provided by Thymeleaf. Since this process was implemented by Processor this time, it inherits the abstract class ʻAbstractProcessorDialect`.

public class KurukuruzDialect extends AbstractProcessorDialect {
  ...
}

constructor

Be sure to create a constructor and define how the Dialect will be used.

  private static final String NAME = "kurukuruz original dialect";
  private static final String PREFIX = "krz";

  public KurukuruzDialect() {
		  super(NAME, PREFIX, StandardDialect.PROCESSOR_PRECEDENCE);
	}

In addition, each argument of the constructor of ʻAbstractProcessorDialect` which is the inheritance source class is as follows.

Processor registration

ʻThe instance of each Procedureor registered in the dialect in getProcessors, which is the abstract method of AbstractProcessorDialect`, is collected as a Set and returned.

  @Override
  public Set<IProcessor> getProcessors(String dialectPrefix) {
    Set<IProcessor> proccessors = new HashSet<>();

    proccessors.add(new BreakLineProccessor(dialectPrefix, getDialectProcessorPrecedence()));

    return proccessors;
  }

Set in Bean

Create a Bean definition method as shown below in an appropriate class with the @Bean annotation enabled, and register the Dialect instance.

 @Bean
 KurukuruzDialect kurukuruzDialect() {
   return new KurukuruzDialect();
 }

Execution result

• HTML template

<body>
<div krz:brtext="${text1}"></div>
<div krz:brtext="${text2}"></div>
<div krz:brtext="${text3}"></div>
<div krz:brtext="${text4}"></div>
<div krz:brtext="${text5}"></div>
</body>

• Model to be displayed

model.addAttribute("text1", "No line breaks");
model.addAttribute("text2", "CRLF line break\r\n Yes\r\n\r\n ↑ 2 consecutive line breaks");
model.addAttribute("text3", "CR line break\with r");
model.addAttribute("text4", "LF line break\n Yes");
model.addAttribute("text5", null);

↓↓↓↓↓

• Output result (html)

<body>
<div>No line breaks</div>
<div>CRLF line break<br>Yes<br><br>↑ 2 consecutive line breaks</div>
<div>CR line break<br>Yes</div>
<div>LF line break<br>Yes</div>
<div></div>
</body>

• Output result (screen display)

Reference site

Thymeleaf converts line feed code to html line feed tag and outputs --Qiita Make your own Dialect with Thymeleaf3 --Qiita [Implement Dialect in thymeleaf3 --abcdefg .....](http: //pppurple.hatenablog.com/entry/2017/03/22/225114)