HttpHeaders (Java SE 9 & JDK 9 )

```
public interface HttpHeaders
```
A read-only view of a set of HTTP headers.
Incubating Feature. Will be removed in a future release.

Since:

9

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`List<String>`	`allValues(String name)`	Returns an unmodifiable List of all of the values of the given named header.
`Optional<String>`	`firstValue(String name)`	Returns an `Optional` containing the first value of the given named (and possibly multi-valued) header.
`OptionalLong`	`firstValueAsLong(String name)`	Returns an `OptionalLong` containing the first value of the named header field.
`Map<String,List<String>>`	`map()`	Returns an unmodifiable multi Map view of this HttpHeaders.

- Method Detail
  - firstValue
```
Optional<String> firstValue(String name)
```
    Returns an Optional containing the first value of the given named (and possibly multi-valued) header. If the header is not present, then the returned Optional is empty.
    
    Parameters:
    
    name - the header name
    
    Returns:
    
    an Optional<String> for the first named value
  - firstValueAsLong
```
OptionalLong firstValueAsLong(String name)
```
    Returns an OptionalLong containing the first value of the named header field. If the header is not present, then the Optional is empty. If the header is present but contains a value that does not parse as a Long value, then an exception is thrown.
    
    Parameters:
    
    name - the header name
    
    Returns:
    
    an OptionalLong
    
    Throws:
    
    NumberFormatException - if a value is found, but does not parse as a Long
  - allValues
```
List<String> allValues(String name)
```
    Returns an unmodifiable List of all of the values of the given named header. Always returns a List, which may be empty if the header is not present.
    
    Parameters:
    
    name - the header name
    
    Returns:
    
    a List of String values
  - map
```
Map<String,List<String>> map()
```
    Returns an unmodifiable multi Map view of this HttpHeaders. This interface should only be used when it is required to iterate over the entire set of headers.
    
    Returns:
    
    the Map