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

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package org.apache.james.mime4j.stream;

import org.apache.james.mime4j.MimeException;
import org.apache.james.mime4j.util.ByteArrayBuffer;

/**
 * <p>
 * Field builders are intended to construct {@link RawField} instances from multiple lines
 * contained in {@link ByteArrayBuffer}s.
 * </p>
 * <p>
 * Field 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 field builder 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 RawField}.</li>
 * <li>Invoke {@link #append(ByteArrayBuffer)} method one or multiple times in order to build
 *   an internal representation of a MIME field from individual lines of text.</li>
 * <li>Optionally {@link #getRaw()} method can be invoked in order to get combined content
 *   of all lines processed so far. Please note builder implementations can return
 *   <code>null</code> if they do not retain original raw content.</li>
 * <li>Invoke {@link #build()} method in order to generate a {@link RawField} instance
 *   based on the internal state of the builder.</li>
 * </ul>
 */
public interface FieldBuilder {

    /**
     * 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 line of text.
     */
    void append(ByteArrayBuffer line) throws MimeException;

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

    /**
     * Returns combined content of all lines processed so far or <code>null</code>
     * if the builder does not retain original raw content.
     */
    ByteArrayBuffer getRaw();

}