How can I use '<' in the value attribute of a component [duplicate]

问题

This question already has an answer here:

How to insert special characters like & and < into JSF components' value attribute? (1 answer)

Closed 2 years ago.

When I try to name my a4j:commandButton by the value <<
Like that

<a4j:commandButton id="myButton" 
    value="<<"
    render="myGrid"
    styleClass="style_btn"
    disabled="false" />

There is an error occure

My debugging trace

Error Traced[line: 88] The value of attribute "value" associated with an element type "null" must not contain the '<' character.] with root cause
javax.faces.view.facelets.FaceletException: Error Parsing /screens/s1.xhtml: Error Traced[line: 88] The value of attribute "value" associated with an element type "null" must not contain the '<' character.
    at com.sun.faces.facelets.compiler.SAXCompiler.doCompile(SAXCompiler.java:390)
    at com.sun.faces.facelets.compiler.SAXCompiler.doCompile(SAXCompiler.java:364)

回答1:

Use XML/HTML entities to insert < or > in an XML file :

value="<<"

来源：https://stackoverflow.com/questions/21707815/how-can-i-use-in-the-value-attribute-of-a-component