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>