06 Request & Response

请求行
请求头
空行
请求体

响应行
响应头
空行
响应体

POST /admin/auth/login HTTP/1.1
Host: 39.101.189.16:8083
Connection: keep-alive
Content-Length: 45
Accept: application/json, text/plain, */*
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36
Content-Type: application/json;charset=UTF-8

{"username":"admin123","password":"admin123"}

HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Set-Cookie: JSESSIONID=24287278-5ebb-407d-a3f7-56b74782c4c7; Path=/; HttpOnly
Content-Length: 200

{"errno":0,"data":{"nickName":"admin123"},"errmsg":"成功"}

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
    // req 负责拿请求信息
    // resp 负责写响应结果
}

POST /demo/login?username=zhangsan HTTP/1.1

@WebServlet("/line")
public class LineServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        System.out.println(req.getMethod());
        System.out.println(req.getRequestURL());
        System.out.println(req.getRequestURI());
        System.out.println(req.getContextPath());
        System.out.println(req.getQueryString());
        System.out.println(req.getProtocol());
    }
}

Host: localhost:8080
User-Agent: Mozilla/5.0
Accept: application/json, text/plain, */*
Content-Type: application/json;charset=UTF-8

Enumeration<String> headerNames = req.getHeaderNames();
while (headerNames.hasMoreElements()) {
    String name = headerNames.nextElement();
    System.out.println(name + ": " + req.getHeader(name));
}

String host = req.getHeader("Host");
String userAgent = req.getHeader("User-Agent");

System.out.println("客户端: " + req.getRemoteAddr() + ":" + req.getRemotePort());
System.out.println("服务器: " + req.getLocalAddr() + ":" + req.getLocalPort());

req.getRequestDispatcher("/target.jsp").forward(req, resp);

req.setAttribute("user", user);
req.getRequestDispatcher("/success.jsp").forward(req, resp);

BufferedReader reader = req.getReader();
String line;
StringBuilder sb = new StringBuilder();
while ((line = reader.readLine()) != null) {
    sb.append(line);
}
System.out.println(sb.toString());

ServletInputStream inputStream = req.getInputStream();
byte[] buffer = new byte[1024];
int len;
while ((len = inputStream.read(buffer)) != -1) {
    System.out.write(buffer, 0, len);
}

String username = req.getParameter("username");
String[] hobbies = req.getParameterValues("hobby");
Map<String, String[]> paramMap = req.getParameterMap();

hobby=sing&hobby=dance

{
  "hobby": ["sing", "dance"]
}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {
    req.setCharacterEncoding("UTF-8");
    String username = req.getParameter("username");
}

User user = new User();
user.setUsername(req.getParameter("username"));
user.setPassword(req.getParameter("password"));

<dependency>
    <groupId>commons-beanutils</groupId>
    <artifactId>commons-beanutils</artifactId>
    <version>1.9.4</version>
</dependency>

import org.apache.commons.beanutils.BeanUtils;

User user = new User();
BeanUtils.populate(user, req.getParameterMap());

<form action="/demo/upload" method="post" enctype="multipart/form-data">
    用户名：<input type="text" name="username"><br>
    头像：<input type="file" name="avatar"><br>
    <input type="submit" value="上传">
</form>

@MultipartConfig
@WebServlet("/upload")
public class UploadServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        String username = req.getParameter("username");
        Part avatarPart = req.getPart("avatar");

        String fileName = avatarPart.getSubmittedFileName();
        long size = avatarPart.getSize();
        String contentType = avatarPart.getContentType();

        String savePath = getServletContext().getRealPath("/uploads");
        avatarPart.write(savePath + File.separator + fileName);
    }
}

resp.setStatus(200);
resp.setStatus(302);
resp.setStatus(404);
resp.setStatus(500);

resp.setHeader("key", "value");

resp.setContentType("text/html;charset=UTF-8");
PrintWriter writer = resp.getWriter();
writer.write("<h1>Hello</h1>");
writer.write("<p>你好</p>");

resp.setContentType("image/jpeg");
InputStream is = getServletContext().getResourceAsStream("/images/photo.jpg");
ServletOutputStream os = resp.getOutputStream();

byte[] buffer = new byte[1024];
int len;
while ((len = is.read(buffer)) != -1) {
    os.write(buffer, 0, len);
}

resp.setContentType("application/json;charset=UTF-8");
resp.getWriter().write("{\"code\":200}");

resp.setHeader("Content-Disposition", "attachment;filename=report.pdf");
resp.setContentType("application/pdf");

resp.setStatus(302);
resp.setHeader("Location", "https://www.example.com");

resp.sendRedirect("https://www.example.com");

resp.setHeader("Refresh", "1");
resp.setHeader("Refresh", "3;url=/login.html");

Class<UserServiceImpl> c1 = UserServiceImpl.class;

UserServiceImpl service = new UserServiceImpl();
Class<? extends UserServiceImpl> c2 = service.getClass();

Class<?> c3 = Class.forName("com.cskaoyan.service.UserServiceImpl");

Class.forName(...)

Field field = clazz.getDeclaredField("username");
field.setAccessible(true);
field.set(instance, "zhangsan");

Method method = clazz.getDeclaredMethod("login", String.class);
method.setAccessible(true);
Object result = method.invoke(instance, "admin");

/user/login
/user/register
/user/delete

String uri = req.getRequestURI();
String methodName = uri.substring(uri.lastIndexOf("/") + 1);
Method method = this.getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
method.invoke(this, req, resp);

浏览器发起 HTTP 请求
    ->
Tomcat 封装为 HttpServletRequest / HttpServletResponse
    ->
Servlet 从 Request 中读取方法、头、参数、请求体
    ->
业务逻辑处理
    ->
Servlet 通过 Response 设置状态码、响应头、响应体
    ->
浏览器按响应头解释并展示结果