问题:

Writing a JSP page, what exactly does the <c:out> do? I've noticed that the following both has the same result:

<p>The person's name is <c:out value="${person.name}" /></p>
<p>The person's name is ${person.name}</p>

回答1:

c:out escapes HTML characters so that you can avoid cross-site scripting.

if person.name = <script>alert("Yo")</script>

the script will be executed in the second case, but not when using c:out

As said Will Wagner, in old version of jsp you should always use c:out to output dynamic text.

Moreover, using this syntax:

<c:out value="${person.name}">No name</c:out>

you can display the text "No name" when name is null.

c:out also has an attribute for assigning a default value if the value of person.name happens to be null.

Source: out (TLDDoc Generated Documentation)

You can explicitly enable escaping of Xml entities by using an attribute escapeXml value equals to true. FYI, it's by default "true".

Older versions of JSP did not support the second syntax.