Miscellaneous Tags

The catch tag provides a complement to the JSP error page mechanism. It allows page authors to recover gracefully from error conditions that they can control. Actions that are of central importance to a page should not be encapsulated in a catch; in this way their exceptions will propagate instead to an error page. Actions with secondary importance to the page should be wrapped in a catch so that they never cause the error page mechanism to be invoked.

The exception thrown is stored in the variable identified by var, which always has page scope. If no exception occurred, the scoped variable identified by var is removed if it existed. If var is missing, the exception is simply caught and not saved.

The out tag evaluates an expression and outputs the result of the evaluation to the current JspWriter object. The syntax and attributes are as follows:

<c:out value="value" [escapeXml="{true|false}"]
     [default="defaultValue"] />

If the result of the evaluation is a java.io.Reader object, then data is first read from the Reader object and then written into the current JspWriter object. The special processing associated with Reader objects improves performance when a large amount of data must be read and then written to the response.

If escapeXml is true, the character conversions listed in Table 7–3 are applied.