Expressions - The J2EE 1.4 Tutorial

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 creates a JAX-RPC stub, sets the endpoint on the stub, and then invokes the sayHello method on the stub, passing the user name retrieved from a request parameter:

<%  
    String resp = null;
    try {
      Stub stub = (Stub)(new
        MyHelloService_Impl().getHelloIFPort());
      stub._setProperty(
        javax.xml.rpc.Stub.ENDPOINT_ADDRESS_PROPERTY,
        "http://localhost:8080/hello-jaxrpc/hello");
      HelloIF hello = (HelloIF)stub;
      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> 

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