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This page explains how to create and configure a custom Filter. 

Please read about Filters  and request processing which explains some filters used by Magnolia. 

Implementation

To ensure your filter is properly registered using Magnolia configuration, your filter should implement 

Example:

public class KlackerFilter extends AbstractMgnlFilter{
    @Override
    public void doFilter(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, 
          FilterChain filterChain) throws IOException, ServletException {
        httpServletResponse.setHeader("X-Clacks-Overhead", "GNU Terry Pratchett" );
        filterChain.doFilter(httpServletRequest, httpServletResponse);
    }
}

The example above is a dummy example inspired by GNU Terry Pratchett HTTP-Header.

Configuration and Registration of filters

Filters in a Java webapp using servlets 2.5 must be registered in the web.xml. However:

You can configure filters implementing 

As with any other configuration data - bootstrap the configuration within your module with a bootstrap file or create an installation task to ensure configuration is set correctly when your project must be reinstalled or deployed.

Add a node to /server/filters

To configure a filter add a node to /server/filters:

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Configuring and registering a filter which does not implement info.magnolia.cms.filters.MgnlFilter

If you have a filter which can not implement 

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Adding filter init parameters

javax.servlet.Filter has an #init method which is called once when the filter is initialized. 

Init parameters for filters implementing info.magnolia.cms.filters.MgnlFilter

When using filters implementing 

public class KlackerFilter extends AbstractMgnlFilter {
	// bean properties
    private String klackerMessage;
    private int maximumKlackerNumber;

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        super.init(filterConfig);
        // use bean properties - here klackerMessage, maximumKlackerNumber - 
        // to do something usefull
    }

    @Override
    public void doFilter(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse,
                         FilterChain filterChain) throws IOException, ServletException {
		// do something usefull here
        filterChain.doFilter(httpServletRequest, httpServletResponse);
    }


	// getter and setter methods for the bean properties
    public String getKlackerMessage() {
        return klackerMessage;
    }
    public void setKlackerMessage(String klackerMessage) {
        this.klackerMessage = klackerMessage;
    }
    public int getMaximumKlackerNumber() {
        return maximumKlackerNumber;
    }
    public void setMaximumKlackerNumber(int maximumKlackerNumber) {
        this.maximumKlackerNumber = maximumKlackerNumber;
    }
}

Init parameters for filters not implementing info.magnolia.cms.filters.MgnlFilter

If you are using FilterDecorator for custom filters not implementing 

public class AnotherFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
		String initParam = filterConfig.get("myInitParam");
		// do something usefull here with the initParam
    }
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) 
      throws IOException, ServletException {
		// do something usefull here
        filterChain.doFilter(servletRequest, servletResponse);
    }
    @Override
    public void destroy() {
    }
}

Ensure position in filter chain

Filters are executed in the order they are in the chain, from top to bottom. If you do not care about execution order, you can skip this section, otherwise make sure the filter is in the right position in the chain. 

Magnolia provides task classes to adapt the order of the filter via module version handler. Use 

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public class MyModuleVersionHandler extends DefaultModuleVersionHandler {
    @Override
    protected List<Task> getExtraInstallTasks(InstallContext installContext) {
        List<Task> extraInstallTasks = new ArrayList<Task>(super.getExtraInstallTasks(installContext));
        extraInstallTasks.add(new FilterOrderingTask("klacker", new String[]{"contentType"}));
        return extraInstallTasks;
    }
}

The code above would ensure to have the filter "klacker" right after the filter "contentType".