SimpleTag (JSP 3.1 API Documentation - Apache Tomcat 10.1.55)
Description: declaration: package: jakarta.servlet.jsp.tagext, interface: SimpleTag

# Interface SimpleTag

All Superinterfaces:
  `JspTag`

All Known Implementing Classes:
  `SimpleTagSupport`

public interface SimpleTag extends JspTag
Interface for defining Simple Tag Handlers.

Simple Tag Handlers differ from Classic Tag Handlers in that instead of supporting `doStartTag()` and `doEndTag()`, the `SimpleTag` interface provides a simple `doTag()` method, which is called once and only once for any given tag invocation. All tag logic, iteration, body evaluations, etc. are to be performed in this single method. Thus, simple tag handlers have the equivalent power of `BodyTag`, but with a much simpler lifecycle and interface.

To support body content, the `setJspBody()` method is provided. The container invokes the `setJspBody()` method with a `JspFragment` object encapsulating the body of the tag. The tag handler implementation can call `invoke()` on that fragment to evaluate the body as many times as it needs.

A SimpleTag handler must have a public no-args constructor. Most SimpleTag handlers should extend SimpleTagSupport.

Lifecycle

The following is a non-normative, brief overview of the SimpleTag lifecycle. Refer to the JSP Specification for details.

1. A new tag handler instance is created each time by the container by calling the provided zero-args constructor. Unlike classic tag handlers, simple tag handlers are never cached and reused by the JSP container.
2. The `setJspContext()` and `setParent()` methods are called by the container. The `setParent()` method is only called if the element is nested within another tag invocation.
3. The setters for each attribute defined for this tag are called by the container.
4. If a body exists, the `setJspBody()` method is called by the container to set the body of this tag, as a `JspFragment`. If the action element is empty in the page, this method is not called at all.
5. The `doTag()` method is called by the container. All tag logic, iteration, body evaluations, etc. occur in this method.
6. The `doTag()` method returns and all variables are synchronized.

Since:
  JSP 2.0
See Also:
  - `SimpleTagSupport`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `doTag()`
  Called by the container to invoke this tag.
  `JspTag`
  `getParent()`
  Returns the parent of this tag, for collaboration purposes.
  `void`
  `setJspBody(JspFragment jspBody)`
  Provides the body of this tag as a JspFragment object, able to be invoked zero or more times by the tag handler.
  `void`
  `setJspContext(JspContext pc)`
  Called by the container to provide this tag handler with the `JspContext` for this invocation.
  `void`
  `setParent(JspTag parent)`
  Sets the parent of this tag, for collaboration purposes.

- ## Method Details

  - ### doTag

    void doTag() throws JspException, IOException
    Called by the container to invoke this tag. The implementation of this method is provided by the tag library developer, and handles all tag processing, body iteration, etc.

    The JSP container will resynchronize any AT_BEGIN and AT_END variables (defined by the associated tag file, TagExtraInfo, or TLD) after the invocation of doTag().

    Throws:
      `JspException` - If an error occurred while processing this tag.
      `SkipPageException` - If the page that (either directly or indirectly) invoked this tag is to cease evaluation. A Simple Tag Handler generated from a tag file must throw this exception if an invoked Classic Tag Handler returned SKIP_PAGE or if an invoked Simple Tag Handler threw SkipPageException or if an invoked Jsp Fragment threw a SkipPageException.
      `IOException` - If there was an error writing to the output stream.

  - ### setParent

    void setParent(JspTag parent)
    Sets the parent of this tag, for collaboration purposes.

    The container invokes this method only if this tag invocation is nested within another tag invocation.

    Parameters:
      `parent` - the tag that encloses this tag

  - ### getParent

    JspTag getParent()
    Returns the parent of this tag, for collaboration purposes.
    Returns:
      the parent of this tag

  - ### setJspContext

    void setJspContext(JspContext pc)
    Called by the container to provide this tag handler with the `JspContext` for this invocation. An implementation should save this value.
    Parameters:
      `pc` - the page context for this invocation
    See Also:
      - `Tag.setPageContext(PageContext)`

  - ### setJspBody

    void setJspBody(JspFragment jspBody)
    Provides the body of this tag as a JspFragment object, able to be invoked zero or more times by the tag handler.

    This method is invoked by the JSP page implementation object prior to `doTag()`. If the action element is empty in the page, this method is not called at all.

    Parameters:
      `jspBody` - The fragment encapsulating the body of this tag.