Candid’s brain

Removing useless newlines from JSP output

Posted on: April 27th, 2010

What has always bothered me the most about JSP was the hundreds of useless newlines that the output produced. Take the following example code:

<html>
    <body>
        <ul>
<%
    for(int i=0; i<3; i++) {
%>
            <li><%=i%></li>
<%
    }
%>
        </ul>
    </body>
</html>

Now look at the output:

<html>
    <body>
        <ul>

            <li>0</li>


            <li>1</li>


            <li>2</li>

        </ul>
    </body>
</html>

The additional newlines are inserted because the line-breaks after the %> are preserved. Not only does this look stupid, it can also create invalid XML if the newlines occur before the <?xml declaration.

One solution would be to omit the newlines after the %>, but obviously this would make correct indentation of the HTML code inside your JSP file impossible as some lines would be preceded by two additional characters.

JSP 2.1 has introduced a trimDirectiveWhitespace parameter [source], which is included in the @page directive: <%@page trimDirectiveWhitespaces="true"%>. Look what the HTML output looks like now:

<html>
    <body>
        <ul>
<li>0</li>
<li>1</li>
<li>2</li>
</ul>
    </body>
</html>

The trimDirectiveWhitespaces parameter not only trims the newlines after the %>, but it trims all white spaces, including the indentation of the next line! I cannot imagine how anyone could have such a stupid idea.

My solution is to replace the newlines automatically in the JSP files before deploying them to the web container. This way, both the JSP file I write and the HTML code that is created look proper. To perform this task, there exists a Maven plugin called maven-replacer-plugin. This is the configuration I use in my pom.xml file:

<pluginRepositories>
    <pluginRepository>
        <id>maven-replacer-plugin reposoitory</id>
        <url>http://maven-replacer-plugin.googlecode.com/svn/release-repo</url>
    </pluginRepository>
</pluginRepositories>
<build>
    <plugins>
        <plugin>
            <groupId>com.google.code.maven-replacer-plugin</groupId>
            <artifactId>maven-replacer-plugin</artifactId>
            <version>1.3.1</version>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>replace</goal>
                    </goals>
                </execution>
            </executions>
            <configuration>
                <includes>
                    <include>target/${project.build.finalName}/**/*.jsp</include>
                </includes>
                <basedir>${basedir}</basedir>
                <replacements>
                    <replacement>
                        <token>(--%&gt;)(\n)</token>
                        <value>$2$1</value>
                    </replacement>
                    <replacement>
                        <token>(%&gt;)(\n)</token>
                        <value>$2$1</value>
                    </replacement>
                </replacements>
                <regexFlags>
                    <regexFlag>MULTILINE</regexFlag>
                </regexFlags>
            </configuration>
        </plugin>
    </plugins>
</build>

This moves the newline behind the %> before it. JSP comments (ending with --%>) are handled separately to not break them. By only moving the newline and not removing it, the line numbers in error messages are still correct. Look at the output now:

<html>
    <body>
        <ul>
            <li>0</li>
            <li>1</li>
            <li>2</li>
        </ul>
    </body>
</html>

Unfortunately, I have not yet found a way to use this together with maven-jspc-plugin, which accesses the JSP files from the source folder directly, so the replacement does not have any effect when you pre-compile your JSP files.

Update: Feel free to copy from my adventurous way of compiling the whitespace-fixed JSP files.

1 Comment Filed under bugs