问题:

While working with JSP files and servlets , I came across <% … %> and <%= … %> .

What's the difference between both cases ?

Thanks

回答1:

<%= … %> will echo out a variable, where as <% … %> denotes a script or some code that is executed.

Here are the links to the jsp documentation:

Expression (<%= … %>) : http://java.sun.com/products/jsp/tags/11/syntaxref11.fm4.html
Scriptlet (<% … %>) : http://java.sun.com/products/jsp/tags/11/syntaxref11.fm5.html

回答2:

<%= new java.util.Date() %>

is same as

<% out.println(new java.util.Date()) %>

There are three types of Scriptlets :

Scriptlet Expressions of the form <%= expression %> that are evaluated and inserted into the output
Scriptlet of the form <% code %> that are inserted into the servlet's service method
Scriptlet Declarations of the form <%! code %> that are inserted into the body of the servlet class, outside of any existing methods. For ex:
```
<%!

public int sum(int a, int b) {

return a + b;
}

%>
```

回答3:

In case of <% ... %> you are adding a server side code. And in case of <%= ... %> you are adding a server side code that automatically prints something. It could be seen as a shortcut for <% out.print( something ) %>.