1、创建HttpRequest对象

HttpRequest对象中的属性与HTTP协议中的内容对应，用于后序servlet从request中获取请求中的参数。

参照http请求报文：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

public class HttpRequest {
    private String method;
    private String url;
    private String version;
    // 存储请求头中的KV
    private Map<String, String> headers = new HashMap<>();
    // url 中的参数和 body 中的参数都放到这个 parameters hash 表中.
    private Map<String, String> parameters = new HashMap<>();
    // 存储Cookie
    private Map<String, String> cookies = new HashMap<>();
    private String body;

    public static HttpRequest build(InputStream inputStream) throws IOException {
        HttpRequest request = new HttpRequest();
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
        // 1. 处理首行 GET /url /HTTP/1.1
        String firstLine = bufferedReader.readLine();
        String[] firstLineTokens = firstLine.split(" ");
        request.method = firstLineTokens[0];
        request.url = firstLineTokens[1];
        request.version = firstLineTokens[2];
        // 2. 解析 url
        int pos = request.url.indexOf("?");
        //2.1 如果有？号，也间接说明这是一个GET请求
        if (pos != -1) {
            // 2.1.1截取出所有参数
            String queryString = request.url.substring(pos + 1);
            // 2.2.2将参数解析为KV后存储
            parseKV(queryString, request.parameters);
        }
        // 3. 循环处理 header 部分
        String line = "";
        while ((line = bufferedReader.readLine()) != null && line.length() != 0) {
            String[] headerTokens = line.split(": ");
            request.headers.put(headerTokens[0], headerTokens[1]);
        }
        // 4. 解析 cookie
        String cookie = request.headers.get("Cookie");
        if (cookie != null) {
            // 把 cookie 进行解析
            parseCookie(cookie, request.cookies);
        }
        // 5. 解析 body
        if ("POST".equalsIgnoreCase(request.method)
                || "PUT".equalsIgnoreCase(request.method)) {
            // 这两个方法需要处理 body, 其他方法暂时不考虑
            // 需要把 body 读取出来.
            // 需要先知道 body 的长度. Content-Length 就是干这个的.
            // 此处的长度单位是 "字节"
            int contentLength = Integer.parseInt(request.headers.get("Content-Length"));
            // 注意体会此处的含义~~
            // 例如 contentLength 为 100 , body 中有 100 个字节.
            // 下面创建的缓冲区长度是 100 个 char (相当于是 200 个字节)
            // 缓冲区不怕长. 就怕不够用. 这样创建的缓冲区才能保证长度管够~~
            char[] buffer = new char[contentLength];
            // 把
            int len = bufferedReader.read(buffer);
            request.body = new String(buffer, 0, len);
            // body 中的格式形如: username=tanglaoshi&password=123
            parseKV(request.body, request.parameters);
        }
        return request;
    }

    private static void parseCookie(String cookie, Map<String, String> cookies) {
        // 1. 按照 分号空格 拆分成多个键值对
        String[] kvTokens = cookie.split("; ");
        // 2. 按照 = 拆分每个键和值
        for (String kv : kvTokens) {
            String[] result = kv.split("=");
            cookies.put(result[0], result[1]);
        }
    }

    private static void parseKV(String queryString, Map<String, String> parameters) {
        // 1. 按照 & 拆分成多个键值对
        String[] kvTokens = queryString.split("&");
        // 2. 按照 = 拆分每个键和值
        for (String kv : kvTokens) {
            String[] result = kv.split("=");
            parameters.put(result[0], result[1]);
        }
    }

    public String getMethod() {
        return method;
    }

    public String getUrl() {
        return url;
    }

    public String getVersion() {
        return version;
    }

    public String getBody() {
        return body;
    }

    public String getParameter(String key) {
        return parameters.get(key);
    }

    public String getHeader(String key) {
        return headers.get(key);
    }

    public String getCookie(String key) {
        return cookies.get(key);
    }
}

2、创建HttpResponse对象

参照http请求报文：

import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.util.HashMap;
import java.util.Map;

public class HttpResponse {
    private String version = "HTTP/1.1";
    private int status;
    private String message;
    private Map<String, String> headers = new HashMap<>();
    private StringBuilder body = new StringBuilder();
    private OutputStream outputStream = null;

    public static HttpResponse build(OutputStream outputStream) {
        HttpResponse response = new HttpResponse();
        response.outputStream = outputStream;
        return response;
    }

    public void setVersion(String version) {
        this.version = version;
    }

    public void setStatus(int status) {
        this.status = status;
    }

    public void setMessage(String message) {
        this.message = message;
    }

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

    public void writeBody(String content) {
        body.append(content);
    }

    public void flush() throws IOException {
        BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream));
        bufferedWriter.write(version + " " + status + " " + message + "\n");
        headers.put("Content-Length", body.toString().getBytes().length + "");
        for (Map.Entry<String, String> entry : headers.entrySet()) {
            bufferedWriter.write(entry.getKey() + ": " + entry.getValue() + "\n");
        }
        bufferedWriter.write("\n");
        bufferedWriter.write(body.toString());
        bufferedWriter.flush();
    }
}