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019    
020    package org.apache.james.mime4j.stream;
021    
022    import org.apache.james.mime4j.MimeException;
023    
024    /**
025     * Body descriptor builders are intended to construct {@link BodyDescriptor} instances from
026     * multiple unstructured {@link RawField}s.
027     * <p/>
028     * Body descriptor builders are stateful and modal as they have to store intermediate results
029     * between method invocations and also rely on a particular sequence of method invocations
030     * (the mode of operation).
031     * <p/>
032     * Consumers are expected to interact with body descriptor builders in the following way:
033     * <ul>
034     * <li>Invoke {@link #reset()} method in order to reset builder's internal state and make it
035     *   ready to start the process of building a new {@link BodyDescriptor}.</li>
036     * <li>Invoke {@link #addField(RawField)} multiple times method in order to collect
037     *   necessary details for building a body descriptor. The builder can optionally
038     *   transform the unstructured field given an an input into a structured one and return
039     *   an instance {@link Field} that also implements a richer interface for a particular type
040     *   of fields such as <code>Content-Type</code>. The builder can also return <code>null</code>
041     *   if the field is to be ignored</li>
042     * <li>Optionally invoke {@link #newChild()} for each embedded body of content. Please note that
043     *   the resultant {@link BodyDescriptorBuilder}} child instance can inherit some its parent
044     *   properties such as MIME type.</li>
045     * <li>Invoke {@link #build()()} method in order to generate a {@link BodyDescriptor}} instance
046     *   based on the internal state of the builder.</li>
047     * </ul>
048     */
049    public interface BodyDescriptorBuilder {
050    
051        /**
052         * Resets the internal state of the builder making it ready to process new input.
053         */
054        void reset();
055    
056        /**
057         * Updates builder's internal state by adding a new field. The builder can optionally
058         * transform the unstructured field given an an input into a structured one and return
059         * an instance {@link Field} that also implements a richer interface for a particular type
060         * of fields such as <code>Content-Type</code>. The builder can also return <code>null</code>
061         * if the field is to be ignored.
062         */
063        Field addField(RawField field) throws MimeException;
064    
065        /**
066         * Builds an instance of {@link BodyDescriptor} based on the internal state.
067         */
068        BodyDescriptor build();
069    
070        /**
071         * Creates an instance of {@link BodyDescriptorBuilder} to be used for processing of an
072         * embedded content body. Please the child instance can inherit some of its parent properties
073         * such as MIME type.
074         */
075        BodyDescriptorBuilder newChild();
076    
077    }