Form Part Customization

/**
 * Builder for individual form body parts with custom header support
 */
public class FormBodyPartBuilder {
    /**
     * Create a form body part builder with name and content body
     * @param name Field name for the form part
     * @param body Content body implementation for the part data
     * @return New FormBodyPartBuilder instance for method chaining
     */
    public static FormBodyPartBuilder create(String name, ContentBody body);
    
    /**
     * Create an empty form body part builder
     * @return New FormBodyPartBuilder instance for method chaining
     */
    public static FormBodyPartBuilder create();
    
    /**
     * Set the field name for the form part
     * @param name Field name to use in Content-Disposition header
     * @return This builder instance for method chaining
     */
    public FormBodyPartBuilder setName(String name);
    
    /**
     * Set the content body for the form part
     * @param body Content body implementation containing the part data
     * @return This builder instance for method chaining
     */
    public FormBodyPartBuilder setBody(ContentBody body);
    
    /**
     * Add a custom header field to the form part
     * @param name Header field name
     * @param value Header field value
     * @return This builder instance for method chaining
     */
    public FormBodyPartBuilder addField(String name, String value);
    
    /**
     * Set a header field, replacing any existing field with the same name
     * @param name Header field name
     * @param value Header field value
     * @return This builder instance for method chaining
     */
    public FormBodyPartBuilder setField(String name, String value);
    
    /**
     * Remove all header fields with the specified name
     * @param name Header field name to remove
     * @return This builder instance for method chaining
     */
    public FormBodyPartBuilder removeFields(String name);
    
    /**
     * Build the configured form body part
     * @return FormBodyPart instance ready for use in multipart entities
     */
    public FormBodyPart build();
}

/**
 * Individual form body part containing headers, name, and content
 * Automatically populates standard headers based on content body properties
 */
public class FormBodyPart {
    /**
     * Get the field name for this form part
     * @return Field name used in Content-Disposition header
     */
    public String getName();
    
    /**
     * Get the content body for this form part
     * @return ContentBody implementation containing the part data
     */
    public ContentBody getBody();
    
    /**
     * Get the header collection for this form part
     * @return Header object containing all headers for this part
     */
    public Header getHeader();
    
    /**
     * Add a header field to this form part
     * @param name Header field name
     * @param value Header field value
     */
    public void addField(String name, String value);
}

/**
 * Container for MIME headers in form parts
 * Supports multiple values for the same header name
 */
public class Header {
    /**
     * Add a header field to the collection
     * @param field MinimalField containing name and value
     */
    public void addField(MinimalField field);
    
    /**
     * Get all header fields
     * @return List of all MinimalField instances
     */
    public List<MinimalField> getFields();
    
    /**
     * Get the first header field with the specified name
     * @param name Header field name to search for
     * @return First matching MinimalField or null if not found
     */
    public MinimalField getField(String name);
    
    /**
     * Get all header fields with the specified name
     * @param name Header field name to search for
     * @return List of all matching MinimalField instances
     */
    public List<MinimalField> getFields(String name);
    
    /**
     * Remove all header fields with the specified name
     * @param name Header field name to remove
     * @return Number of fields removed
     */
    public int removeFields(String name);
    
    /**
     * Set a header field, replacing any existing fields with the same name
     * @param field MinimalField to set (replaces existing fields with same name)
     */
    public void setField(MinimalField field);
    
    /**
     * Iterate over all header fields
     * @return Iterator for all MinimalField instances
     */
    public Iterator<MinimalField> iterator();
}

/**
 * Individual MIME header field with name and value
 */
public class MinimalField {
    /**
     * Create a header field with name and value
     * @param name Header field name
     * @param value Header field value
     */
    public MinimalField(String name, String value);
    
    /**
     * Get the header field name
     * @return Header field name
     */
    public String getName();
    
    /**
     * Get the header field value
     * @return Header field value
     */
    public String getBody();
    
    /**
     * Get formatted header field as "name: value"
     * @return Formatted header field string
     */
    public String toString();
}

/**
 * MIME-related constants and utilities
 */
public class MIME {
    // Header name constants
    public static final String CONTENT_TYPE = "Content-Type";
    public static final String CONTENT_TRANSFER_ENC = "Content-Transfer-Encoding";
    public static final String CONTENT_DISPOSITION = "Content-Disposition";
    
    // Transfer encoding constants
    public static final String ENC_8BIT = "8bit";
    public static final String ENC_BINARY = "binary";
    
    // Character set constants
    public static final Charset DEFAULT_CHARSET; // US-ASCII
    public static final Charset UTF8_CHARSET; // UTF-8
}

import org.apache.http.entity.mime.*;
import org.apache.http.entity.mime.content.*;
import org.apache.http.entity.ContentType;
import java.io.File;

// Basic custom form part with additional headers
FormBodyPart customPart = FormBodyPartBuilder
    .create("document", new FileBody(new File("report.pdf"), ContentType.APPLICATION_PDF))
    .addField("Content-Description", "Monthly Sales Report")
    .addField("X-Document-Type", "financial")
    .addField("X-Department", "sales")
    .build();

// Text part with custom headers
StringBody jsonBody = new StringBody("{\"version\":\"1.0\",\"format\":\"report\"}", 
                                     ContentType.APPLICATION_JSON);
FormBodyPart metadataPart = FormBodyPartBuilder
    .create("metadata", jsonBody)
    .addField("Content-Description", "Report Metadata")
    .addField("X-Schema-Version", "2.1")
    .build();

// Image with custom disposition and headers
ByteArrayBody imageBody = new ByteArrayBody(imageBytes, ContentType.IMAGE_JPEG, "profile.jpg");
FormBodyPart imagePart = FormBodyPartBuilder
    .create("avatar", imageBody)
    .addField("Content-Description", "User Profile Picture")
    .addField("X-Image-Source", "camera")
    .addField("X-Compression", "high")
    .build();

// Use custom parts in multipart entity
HttpEntity entity = MultipartEntityBuilder.create()
    .addPart(customPart)
    .addPart(metadataPart)
    .addPart(imagePart)
    .addTextBody("username", "johndoe")  // Standard parts can be mixed in
    .build();

// Access part properties
String partName = customPart.getName();  // "document"
ContentBody body = customPart.getBody(); // FileBody instance
Header headers = customPart.getHeader();

// Work with headers directly
Header customHeaders = new Header();
customHeaders.addField(new MinimalField("Content-Language", "en-US"));
customHeaders.addField(new MinimalField("X-Priority", "high"));
customHeaders.addField(new MinimalField("X-Department", "engineering"));

// Get header values
MinimalField priority = customHeaders.getField("X-Priority");
List<MinimalField> allFields = customHeaders.getFields();
String priorityValue = priority != null ? priority.getBody() : "normal";

// Complex form part with streaming content and multiple headers
FileInputStream largeFileStream = new FileInputStream("large-dataset.csv");
InputStreamBody streamBody = new InputStreamBody(largeFileStream, 
                                                  ContentType.create("text/csv"), 
                                                  "dataset.csv");

FormBodyPart streamPart = FormBodyPartBuilder
    .create("data", streamBody)
    .addField("Content-Description", "Machine Learning Dataset")
    .addField("X-Data-Format", "CSV")
    .addField("X-Record-Count", "1000000")
    .addField("X-Columns", "name,age,score,category")
    .addField("X-Encoding", "UTF-8")
    .build();