The Java EE 5 Tutorial

JSP Expressions

A JSP expression is used to insert the value of a scripting language expression, converted into a string, into the data stream returned to the client. When the scripting language is the Java programming language, an expression is transformed into a statement that converts the value of the expression into a String object and inserts it into the implicit out object.

The syntax for an expression is as follows:

<%= scripting-language-expression %>

Note that a semicolon is not allowed within a JSP expression, even if the same expression has a semicolon when you use it within a scriptlet.

In the web service version of the hello1 application, response.jsp contains the following scriptlet, which gets the proxy that implements the service endpoint interface. It then invokes the sayHello method on the proxy, passing the user name retrieved from a request parameter:

    String resp = null;
    try {
        Hello hello = new HelloService().getHelloPort();
        resp = hello.sayHello(request.getParameter("username"));
    } catch (Exception ex) {
        resp = ex.toString();

A scripting expression is then used to insert the value of resp into the output stream:

<h2><font color="black"><%= resp %>!</font></h2>