package com.hamishrickerby.http_server;

import java.util.*;

/**
 * Created by rickerbh on 18/08/2016.
 */
public class Headers {
    private static String HEADER_SEPARATOR = ": ";

    Map<String, String> headers;

    public Headers() {
        headers = new HashMap<>();
    }

    public List<String> list() {
        List<String> headerList = new ArrayList<>();
        for (String key : headers.keySet()) {
            headerList.add(key + HEADER_SEPARATOR + headers.get(key));
        }
        return headerList;
    }

    public void put(String key, String value) {
        headers.put(key, value);
    }

    public void parse(String headerString) {
        String[] lines = headerString.split("\r\n");
        for (String line : Arrays.asList(lines)) {
            String[] components = line.split(":");
            put(components[0].trim(), components[1].trim());
        }
    }

    public String get(String key) {
        return headers.getOrDefault(key, "");
    }

}

package com.hamishrickerby.http_server;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

/**
 * Created by rickerbh on 18/08/2016.
 */
public class Headers {
    private static String HEADER_SEPARATOR = ": ";

    Map<String, String> headers;

    public Headers() {
        headers = new HashMap<>();
    }

    public List<String> list() {
        return headers.keySet().stream()
                .map(key -> key + HEADER_SEPARATOR + headers.get(key))
                .collect(Collectors.toList());
    }

    public void put(String key, String value) {
        headers.put(key, value);
    }

    public void parse(String headerString) {
        String[] lines = headerString.split("\r\n");
        for (String line : Arrays.asList(lines)) {
            String[] components = line.split(":");
            put(components[0].trim(), components[1].trim());
        }
    }

    public String get(String key) {
        return headers.getOrDefault(key, "");
    }

}

Refactor headers list() with map/collect
Refactor headers list() with map/collect
