Package org.apache.tomcat.util.http

Class MimeHeaders

java.lang.Object
org.apache.tomcat.util.http.MimeHeaders
public class MimeHeaders extends Object
Memory-efficient repository for Mime Headers. When the object is recycled, it will keep the allocated headers[] and all the MimeHeaderField - no GC is generated.

For input headers it is possible to use the MessageByte for Fields - so no GC will be generated.

The only garbage is generated when using the String for header names/values - this can't be avoided when the servlet calls header methods, but is easy to avoid inside tomcat. The goal is to use _only_ MessageByte-based Fields, and reduce to 0 the memory overhead of tomcat.

This class is used to contain standard internet message headers, used for SMTP (RFC822) and HTTP (RFC2068) messages as well as for MIME (RFC 2045) applications such as transferring typed data and grouping related items in multipart message bodies.

Message headers, as specified in RFC822, include a field name and a field body. Order has no semantic significance, and several fields with the same name may exist. However, most fields do not (and should not) exist more than once in a header.

Many kinds of field body must conform to a specified syntax, including the standard parenthesized comment syntax. This class supports only two simple syntaxes, for dates and integers.

When processing headers, care must be taken to handle the case of multiple same-name fields correctly. The values of such fields are only available as strings. They may be accessed by index (treating the header as an array of fields), or by name (returning an array of string values).

Headers are first parsed and stored in the order they are received. This is based on the fact that most servlets will not directly access all headers, and most headers are single-valued. (the alternative - a hash or similar data structure - will add an overhead that is not needed in most cases)

Apache seems to be using a similar method for storing and manipulating headers.

Author:
dac@eng.sun.com, James Todd [gonzo@eng.sun.com], Costin Manolache, kevin seguin

  • Field Details

    • DEFAULT_HEADER_SIZE

      public static final int DEFAULT_HEADER_SIZE
      Initial size - should be == average number of headers per request
      See Also:

  • Constructor Details

    • MimeHeaders

      public MimeHeaders()
      Creates a new MimeHeaders object using a default buffer size.

  • Method Details

    • setLimit

      public void setLimit(int limit)
      Set limit on the number of header fields.
      Parameters:
      limit - The new limit

    • recycle

      public void recycle()
      Clears all header fields.

    • clear

      @Deprecated public void clear()
      Deprecated.

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • duplicate

      public void duplicate(MimeHeaders source) throws IOException
      Throws:
      IOException

    • size

      public int size()
      Returns:
      the current number of header fields.

    • getName

      public MessageBytes getName(int n)
      Parameters:
      n - The header index
      Returns:
      the Nth header name, or null if there is no such header. This may be used to iterate through all header fields.

    • getValue

      public MessageBytes getValue(int n)
      Parameters:
      n - The header index
      Returns:
      the Nth header value, or null if there is no such header. This may be used to iterate through all header fields.

    • findHeader

      public int findHeader(String name, int starting)
      Find the index of a header with the given name.
      Parameters:
      name - The header name
      starting - Index on which to start looking
      Returns:
      the header index

    • names

      public Enumeration<String> names()
      Returns an enumeration of strings representing the header field names. Field names may appear multiple times in this enumeration, indicating that multiple fields with that name exist in this header.
      Returns:
      the enumeration

    • values

      public Enumeration<String> values(String name)

    • addValue

      public MessageBytes addValue(String name)
      Create a new named header , return the MessageBytes container for the new value
      Parameters:
      name - The header name
      Returns:
      the message bytes container for the value

    • addValue

      public MessageBytes addValue(byte[] b, int startN, int len)
      Create a new named header using un-translated byte[]. The conversion to chars can be delayed until encoding is known.
      Parameters:
      b - The header name bytes
      startN - Offset
      len - Length
      Returns:
      the message bytes container for the value

    • setValue

      public MessageBytes setValue(String name)
      Allow "set" operations, which removes all current values for this header.
      Parameters:
      name - The header name
      Returns:
      the message bytes container for the value

    • getValue

      public MessageBytes getValue(String name)
      Finds and returns a header field with the given name. If no such field exists, null is returned. If more than one such field is in the header, an arbitrary one is returned.
      Parameters:
      name - The header name
      Returns:
      the value

    • getUniqueValue

      public MessageBytes getUniqueValue(String name)
      Finds and returns a unique header field with the given name. If no such field exists, null is returned. If the specified header field is not unique then an IllegalArgumentException is thrown.
      Parameters:
      name - The header name
      Returns:
      the value if unique
      Throws:
      IllegalArgumentException - if the header has multiple values

    • getHeader

      public String getHeader(String name)

    • removeHeader

      public void removeHeader(String name)
      Removes a header field with the specified name. Does nothing if such a field could not be found.
      Parameters:
      name - the name of the header field to be removed

    • removeHeader

      public void removeHeader(int idx)
      Reset, move to the end and then reduce count by 1.
      Parameters:
      idx - the index of the header to remove.