Java Request学习笔记

1.获取请求部分的信息方法：
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@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //设置响应的内容为html，指定编码为utf-8
    response.setContentType("text/html;charset=utf-8");
    //获取打印流
    PrintWriter out = response.getWriter();
    //输出到浏览器端
    out.print("你好，Servlet <br/>");
    //接口的好处：降低tomcat和我们servlet之间的耦合度，以后还可以使用别的web服务器
    out.print("请求对象：" + request + "<hr/>");

    out.print("<h1>请求行</h1>");
    out.print("获取请求方式：" + request.getMethod() + "<br/>");  //GET或POST
    out.print("获取当前模块的访问地址:" + request.getContextPath() + "<br/>");   // day27_02_request_war_exploded
    out.print("获取完整的URL：" + request.getRequestURL() + "<br/>");  //  http://localhost:8888/day27_02_request_war_exploded/Demo1Servlet
    out.print("获取URI:" + request.getRequestURI() + "<br/>");  //  /day27_02_request_war_exploded/Demo1Servlet
    //访问地址：http://localhost:8888/day27_02_request_war_exploded/Demo1Servlet?name=NewBoy&password=123
    out.print("查询字符串(?后面的参数)：" + request.getQueryString() + "<br/>");  //name=NewBoy&password=123
    //out.write()和out.print()区别，是一样的，没有什么区别。print方法重载更多，使用更方便。 print底层调用的就是write方法

    out.print("<h1>请求头</h1>");
    //由键和值组成，通过键获取值。
    out.print("获取user-agent请求头：" + request.getHeader("user-agent") + "<br/>");

    out.print("<h1>请求体</h1>");
    out.print("GET没有请求体<br/>");
    out.print("POST方法获取数据：<br/>");
    //1.得到字符输入流
    BufferedReader br = request.getReader();
    //2.从输入流中读取数据
    String line = br.readLine();
    out.print(line);
}

2.通过request.getParameterMap()直接获取所有参数的map对象

public class Demo2ParamServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //GET请求汉字没有乱码问题，POST请求会有乱码问题，解决方法：在获取参数前设置请求的编码
        request.setCharacterEncoding("utf-8");

        //方式一：获取所有的参数，封装成Map
        //1.获取表单所有的参数，封装成Map，键是String，值是String[]数组
        Map<String, String[]> parameterMap = request.getParameterMap();
        //2.输出所有的参数名和值
        parameterMap.forEach((key,value) -> System.out.println("参数名:" + key + "，参数值：" + Arrays.toString(value)));

        //方式二：通过名字获取一个值，参数名是表单项的名字
        String city = request.getParameter("city");
        System.out.println("获取一个参数：" + city);

        //方式三：通过名字获取一组值，获取字符串的数组
        String[] hobbies = request.getParameterValues("hobby");
        System.out.println("获取一组值：" + Arrays.toString(hobbies));
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

3.修改idea自带的模板代码：
在设置里找到File and Code Templates
在Other里可以找到Servlet Class的模板
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4.设置跳转：

public class Demo3ServletA extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("访问资源A");
        //转发：在服务器端进行页面跳转
        //将数据放在请求作用域中
        request.setAttribute("key", "钥匙");
        //前面部分获取转发器，指定要跳转到的地址，再调用forward方法转发，传递请求和响应对象
        //request.getRequestDispatcher("b").forward(request, response);

        //重定向: 1) 设置状态码为302  2)指定要跳转的地址，设置响应头location
        //response.setStatus(302);
        //response.setHeader("location","b");

        //因为以上2个方法常用，所以也专门设置了重定向的方法
        response.sendRedirect("b");

        //跳转到其它任意的服务器
        //response.sendRedirect("http://www.itheima.com");
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

@WebServlet("/b")  //要跳转到的地址
public class Demo4ServletB extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("访问资源B");

        //1.设置响应内容和编码
        response.setContentType("text/html;charset=utf8");
        //2.获取字符流
        PrintWriter out = response.getWriter();
        //3.输出
        out.println("<h1>资源B</h1>");
        //4.从请求域中获取数据
        out.println(request.getAttribute("key"));
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

5.设置响应头

@WebServlet("/Demo5HeaderServlet")
public class Demo5HeaderServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置一个响应头：设置响应的类型
        //response.setHeader("content-type","text/html;charset=utf-8");
        //因为这个响应头用得很多，所以专门设置了一个方法。如果没有这句，浏览器端汉字会乱码
        //MIME类型：通过类型指定打开资源的方式，格式：大类型/小类型;其它参数
        response.setContentType("text/html;charset=utf-8");
        //获取打印字符流
        PrintWriter out = response.getWriter();
        //输出到浏览器
        out.print("你好，积极响应！");
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

6.输入输出流：
resources里的文件在编译的时候会被打包到类文件夹下

@WebServlet("/Demo6PictureServlet")
public class Demo6PictureServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //0.设置响应类型MIME为图片类型
        response.setContentType("image/jpeg");
        //1.读取图片文件，得到字节输入流 (通过类对象读取根目录下文件)
        //getClass()类对象的getResourceAsStream方法：默认是在当前类所在的包去读取文件
        //getClassLoader()类加载器的getResourceAsStream方法：默认是在类路径的根目录下读取文件
        InputStream inputStream = getClass().getClassLoader().getResourceAsStream("404a.jpg");
        //2.获取响应对象的字节输出流
        ServletOutputStream outputStream = response.getOutputStream();
        //3.将输入流复制到输出流中
        IOUtils.copy(inputStream, outputStream);
        //4.关闭输入输出流
        inputStream.close();
        outputStream.close();
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

7.设置断点debug:
在idea的列号和对应代码之间，点击空白即可看到设置红色的断点
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然后在运行的时候选择虫子模样的debug图标

之后可以在idea里通过调试器一步步看程序里变量的变化

8.在pom.xml里导入mybaits和mysql的坐标

<dependency> 
  <groupId>javax.servlet</groupId>  
  <artifactId>javax.servlet-api</artifactId>  
  <version>3.1.0</version>  
  <scope>provided</scope> 
</dependency>  
<!-- mybatis -->  
<dependency> 
  <groupId>org.mybatis</groupId>  
  <artifactId>mybatis</artifactId>  
  <version>3.5.5</version> 
</dependency>  
<!-- mysql驱动 -->  
<dependency> 
  <groupId>mysql</groupId>  
  <artifactId>mysql-connector-java</artifactId>  
  <version>5.1.22</version> 
</dependency>

9.利用mybatis+servlet编写登录和注册请求

@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //汉字乱码
        request.setCharacterEncoding("utf-8");

        //1.接收用户名和密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        //2.调用Mapper查询，返回User对象
        //2.1 调用工具类得到会话对象
        SqlSession sqlSession = MyBatisUtils.getSession();
        //2.2 由会话对象得到UserMapper的代理对象
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //2.3 调用接口中方法查询
        User user = userMapper.select(username, password);
        //2.4 关闭会话
        sqlSession.close();

        //打印到浏览器上
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        //3.判断User对象是否为null
        if (user == null) {
            //为null：登录失败
            out.print("登录失败，<a href='login.html'>请重试</a>");
        }
        else {
            //不为null：登录成功
            out.print("欢迎您! " + username);
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

@WebServlet("/RegisterServlet")
public class RegisterServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //如果注册有汉字，考虑汉字乱码的问题
        request.setCharacterEncoding("utf-8");

        //1.获取用户名和密码  ctrl+d 复制一行
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        //2.判断用户名是否存在
        SqlSession sqlSession = MyBatisUtils.getSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //通过用户名查找用户
        User user = userMapper.selectByUsername(username);

        //模板代码：rout
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();

        //3.如果存在，提示：注册失败   快捷键：inn 和 ifn
        if (user != null) {
            out.print("用户名：" + username + "，已经存在，<a href='register.html'>请重试</a>");
        }
        //4.否则就添加用户，提示：注册成功
        else {
            //创建一个用户对象
            user = new User();
            //封装属性
            user.setUsername(username);
            user.setPassword(password);
            userMapper.add(user);
            //注：添加要提交事务
            sqlSession.commit();

            //输出注册成功
            out.println("注册成功，<a href='login.html'>请登录</a>");
        }

        //关闭会话
        sqlSession.close();
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}