io.inkstand.halite.rs.HaliteMessageBodyWriter Maven / Gradle / Ivy

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package io.inkstand.halite.rs;

import javax.ws.rs.core.MediaType;
import javax.ws.rs.ext.MessageBodyWriter;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import java.util.Collection;
import java.util.Collections;

import io.inkstand.halite.Resource;

/**
 * {@link MessageBodyWriter} to write halite {@link Resource}s in a JAX-RS service response.
 *  
 * @author Gerald Mücke
 *
 * @param  type of the {@link Resource} to write
 */
public abstract class HaliteMessageBodyWriter implements MessageBodyWriter {

    private String compiledPackageList;
    private Collection compiledMediaTypeList;

    /**
     * Always returns -1 as the size of the compiled output is not determinable
     */
    @Override
    public long getSize(R t, Class type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        return -1;
    }

    /**
     * Override this method to provide a set of {@link MediaType}s that this {@link MessageBodyWriter} will
     * produce. This set is evaluated in teh isWriteable method. The default list is empty and therefore
     * all {@link MediaType}s are considered to be writeable.
     * @return
     *  empty List
     */
    protected Collection getSupportedMediaTypes(){
        return Collections.emptyList();
    }
    
    /**
     * Checks if the type parameter is a {@link Resource}
     */
    @Override
    public boolean isWriteable(Class type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        boolean isResource = Resource.class.isAssignableFrom(type);
        
        if(compiledMediaTypeList == null) {
            this.compiledMediaTypeList = Collections.unmodifiableCollection(getSupportedMediaTypes());
        }        
        //if there is no mediaType set, all mediaTypes are accepted
        boolean isSupportedMediaType = compiledMediaTypeList.isEmpty();
        for(MediaType supportedMediaType : compiledMediaTypeList){
            isSupportedMediaType |= supportedMediaType.equals(mediaType);
        }            
        return isResource && isSupportedMediaType;
    }

    /**
     * Override this method to provide the names of custom model package names. 
     * @return
     *  an empty list
     */
    protected Collection getCustomModelPackages(){
        return Collections.emptyList(); 
    }

    /**
     * Creates a new JAXBContext for the given model packages.
     * @return
     *  a new instance of a JAXBContext
     * @throws JAXBException
     */
    protected JAXBContext newJAXBContext() throws JAXBException {
        return JAXBContext.newInstance(getJAXBModelPackage());
    }

    /**
     * @return
     *  the package containing JAXB model packages. To add additional packages append or prepend custom
     *  packages and use a colon ':' as separator between the backages 
     */
    private String getJAXBModelPackage() {
        if(compiledPackageList == null) {
            StringBuilder buf = new StringBuilder(64);
            //add mandatory package
            buf.append("io.inkstand.halite");
            for(String customPackage: getCustomModelPackages()){
                buf.append(':').append(customPackage);
            }
            compiledPackageList = buf.toString(); 
        }
        return compiledPackageList;
    }

}