core/src/main/java/org/apache/james/mime4j/stream/BodyDescriptorBuilder.java

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package org.apache.james.mime4j.stream;

import org.apache.james.mime4j.MimeException;

/**
 * <p>
 * Body descriptor builders are intended to construct {@link BodyDescriptor} instances from
 * multiple unstructured {@link RawField}s.
 * </p>
 * <p>
 * Body descriptor builders are stateful and modal as they have to store intermediate results
 * between method invocations and also rely on a particular sequence of method invocations
 * (the mode of operation).
 * </p>
 * <p>
 * Consumers are expected to interact with body descriptor builders in the following way:
 * </p>
 * <ul>
 * <li>Invoke {@link #reset()} method in order to reset builder's internal state and make it
 *   ready to start the process of building a new {@link BodyDescriptor}.</li>
 * <li>Invoke {@link #addField(RawField)} multiple times method in order to collect
 *   necessary details for building a body descriptor. The builder can optionally
 *   transform the unstructured field given an an input into a structured one and return
 *   an instance {@link Field} that also implements a richer interface for a particular type
 *   of fields such as <code>Content-Type</code>. The builder can also return <code>null</code>
 *   if the field is to be ignored</li>
 * <li>Optionally invoke {@link #newChild()} for each embedded body of content. Please note that
 *   the resultant {@link BodyDescriptorBuilder}} child instance can inherit some its parent
 *   properties such as MIME type.</li>
 * <li>Invoke {@link #build()} method in order to generate a {@link BodyDescriptor}} instance
 *   based on the internal state of the builder.</li>
 * </ul>
 */
public interface BodyDescriptorBuilder {

    /**
     * Resets the internal state of the builder making it ready to process new input.
     */
    void reset();

    /**
     * Updates builder's internal state by adding a new field. The builder can optionally
     * transform the unstructured field given an an input into a structured one and return
     * an instance {@link Field} that also implements a richer interface for a particular type
     * of fields such as <code>Content-Type</code>. The builder can also return <code>null</code>
     * if the field is to be ignored.
     */
    Field addField(RawField field) throws MimeException;

    /**
     * Builds an instance of {@link BodyDescriptor} based on the internal state.
     */
    BodyDescriptor build();

    /**
     * Creates an instance of {@link BodyDescriptorBuilder} to be used for processing of an
     * embedded content body. Please the child instance can inherit some of its parent properties
     * such as MIME type.
     */
    BodyDescriptorBuilder newChild();

}