JavaWeb_Java

Servlet学习总结 1. Servlet 1.1 Servlet 简介

servlet是sun公司开发动态web的一门技术
sun公司在这些api中提供了一个接口叫做:servlet,如果想要开发一个servlet程序,只需要完成两步
- 编写好一个类实现servlet接口
- 把开发好的java类部署到web服务器中
- 有两个默认实现接口(GenericServlet、HttpServlet)

把实现的servlet接口的java程序叫做,servlet

1.2 Helloservlet

关于父子工程理解:

父工程中会有:

    
        servlet-01

子工程中会有:

    
        hello
        org.example
        1.0-SNAPSHOT

父项目的jar包，子项目可以直接使用类似于多态

maven环境优化
1. 修改web.xml为最新版
2. 将maven的结构搭建完整

编写一个Servlet程序

编写一个普通类

实现servlet接口

public class HelloServlet extends HttpServlet {
//    由于get或者post只是请求的不同方式所以可以相互调用,业务逻辑都一样
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        ServletOutputStream outputStream = resp.getOutputStream();
        PrintWriter writer = resp.getWriter(); // 响应流
        writer.println("hello servlet");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

编写Servlet的映射

为什么需要映射:我们写的的java程序,但是要通过浏览器访问,而浏览器需要连接web服务器,所以我们需要在web服务中注册我们写的Servlet, 还需要给他一个浏览器能够访问的路径
```
    
        HelloServlet
        com.zhang.servlet.HelloServlet
    

    
        HelloServlet
        /zhang
    
 
```
配置tomcat(需添加子项目工件)

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启动测试

1.3 Servlet原理

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1.4 mapping

1. 一个servlet指定一个映射路径

    
        helloServlet
        HelloServlet
    

    
        helloServlet

        /zhangxin

一个servlet指定多个映射路径

    
        helloServlet
        HelloServlet
    

    
        helloServlet

        /zhangxin   
    
        
            helloServlet
            
            /zhangxin2

一个servlet指定通用路径

    
        helloServlet
        
        /*
    
此时不会进入默认的index界面, 可以将/*改为/XXX/*

指定特定后缀等

    
        helloServlet
        
        *.zx

1.5 ServletContext

web容器在启动的时候, 它会为每个web程序都创建一个ServletContext对象, 它代表了当前的web应用;

1. 共享数据

我在这个Servlet中保存的数据可以在另外一个servlet中拿到;

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setCharacterEncoding("utf-8");
//        this.getInitParameter(); 初始化参数
//        this.getServletConfig(); servlet配置
//        this.getServletContext(); 上下文
        ServletContext servletContext = this.getServletContext();
        String username = "zx";
        servletContext.setAttribute("username", username); // 将一个数据保存在servletContext中

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html");
        ServletContext servletContext = this.getServletContext();
//        Object  username = servletContext.getAttribute("username"); 将Object强制转换为 String
        String  username = (String) servletContext.getAttribute("username");
        resp.getWriter().println("姓名:"+ username);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

2. 获取初始化参数


    
        url
        jdbc:mysql://localhost:3306/mybatis

        ServletContext servletContext = this.getServletContext();
//        resp.setCharacterEncoding("utf-8");
//        resp.setContentType("text/html");
        String initParameter = servletContext.getInitParameter("url");  // 获取web.xml初始化参数中的URL
        resp.getWriter().println(initParameter);

    }

3. 请求转发

public class Servlet4 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
//        RequestDispatcher requestDispatcher = servletContext.getRequestDispatcher("/gp");   // 转发的请求路径
//        requestDispatcher.forward(req, resp);   // 调用forward实现请求转发
        servletContext.getRequestDispatcher("/gp").forward(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

4. 读取资源文件

Properties

1. 在java目录下新建properties
1. 在resources目录下新建properties

发现: 都被打包到同一个路径下(classes), 我们俗称这个路径为classpath

思路: 需要一个文件流

username = root
password = 000000

public class Servlet5 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");    // getResourceAsStream将文件转化成流
        Properties prop = new Properties();
        prop.load(is);
        String user = prop.getProperty("username");     // 获取属性
        String pwd = prop.getProperty("password");     // 获取属性
        resp.getWriter().println("username:" + user + "n" + "password:" + pwd);

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

1.6 HttpServletResponse

web服务器接收到客户端的http请求, 针对这个请求, 分别创建一个代表请求的HttpServletRequest对象和一个代表响的HttpServletResponse

如果要获取客户端请求过来的参数: 找HttpServletRequest
如果要获取客户端响应的信息: 找HttpServletResponse

1、简单分类

负责向浏览器发送数据的方法

    ServletOutputStream getOutputStream() throws IOException;

    PrintWriter getWriter() throws IOException;

负责向浏览器发送响应头的方法

    void setCharacterEncoding(String var1);

    void setContentLength(int var1);

    void setContentType(String var1);

    void setDateHeader(String var1, long var2);

    void addDateHeader(String var1, long var2);

    void setHeader(String var1, String var2);

    void addHeader(String var1, String var2);

    void setIntHeader(String var1, int var2);

响应的状态码

    int SC_CONTINUE = 100;
    int SC_SWITCHING_PROTOCOLS = 101;
    int SC_OK = 200;
    int SC_CREATED = 201;
    int SC_ACCEPTED = 202;
    int SC_NON_AUTHORITATIVE_INFORMATION = 203;
    int SC_NO_CONTENT = 204;
    int SC_RESET_CONTENT = 205;
    int SC_PARTIAL_CONTENT = 206;
    int SC_MULTIPLE_CHOICES = 300;
    int SC_MOVED_PERMANENTLY = 301;
    int SC_MOVED_TEMPORARILY = 302;
    int SC_FOUND = 302;
    int SC_SEE_OTHER = 303;
    int SC_NOT_MODIFIED = 304;
    int SC_USE_PROXY = 305;
    int SC_TEMPORARY_REDIRECT = 307;
    int SC_BAD_REQUEST = 400;
    int SC_UNAUTHORIZED = 401;
    int SC_PAYMENT_REQUIRED = 402;
    int SC_FORBIDDEN = 403;
    int SC_NOT_FOUND = 404;
    int SC_METHOD_NOT_ALLOWED = 405;
    int SC_NOT_ACCEPTABLE = 406;
    int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
    int SC_REQUEST_TIMEOUT = 408;
    int SC_CONFLICT = 409;
    int SC_GONE = 410;
    int SC_LENGTH_REQUIRED = 411;
    int SC_PRECONDITION_FAILED = 412;
    int SC_REQUEST_ENTITY_TOO_LARGE = 413;
    int SC_REQUEST_URI_TOO_LONG = 414;
    int SC_UNSUPPORTED_MEDIA_TYPE = 415;
    int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
    int SC_EXPECTATION_FAILED = 417;
    int SC_INTERNAL_SERVER_ERROR = 500;
    int SC_NOT_IMPLEMENTED = 501;
    int SC_BAD_GATEWAY = 502;
    int SC_SERVICE_UNAVAILABLE = 503;
    int SC_GATEWAY_TIMEOUT = 504;
    int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

2、常见应用

1. 向浏览器输出消息（文档前部分内容）

2. 下载文件

	1. 获取下载文件路径
	2. 下载的文件名
	3. 让浏览器能够支持下载我们需要的东西
	4. 获取下载文件的输入流
	5. 创建缓冲区
	6. 获取OutputStream
	7. 将FileOutputStream写入到缓冲区
	8. 使用OutputStream将缓冲区的数据输出到客户端

```java
public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //  1.  获取下载文件路径
        String realPath = "C:\Users\Administrator\Desktop\demo2\hello\out\artifacts\response_Web_exploded\WEB-INF\classes\saber.jpg";
        System.out.println("下载文件的路径" + realPath);
        //  2. 下载的文件名
        String fileName = realPath.substring(realPath.lastIndexOf("\") + 1);
        //  3. 让浏览器能够支持(Content-Disposition)下载我们需要的东西, 中文文件名用URLEncoder.encode, 否则有可能乱码
        //        resp.setHeader("Content-Disposition", "attachment;filename=" + fileName);
        resp.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName ,"utf-8"));
        //  4. 获取下载文件的输入流
        FileInputStream fileInputStream = new FileInputStream(realPath);
        //  5. 创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
        //  6. 获取OutputStream
        ServletOutputStream outputStream = resp.getOutputStream();
        //  7. 将FileOutputStream写入到缓冲区
        while ((len = fileInputStream.read(buffer)) > 0) {
            outputStream.write(buffer, 0, len);
        }
        outputStream.close();
        fileInputStream.close();
        //  8. 使用OutputStream将缓冲区的数据输出到客户端
            }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

3、验证码功能

验证码怎么来的？

前端实现
后端实现，需要用到java的图片类，生成一个图片

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //  如何让浏览器5秒自动刷新一次;
        resp.setHeader("refresh", "5");

        //  在内存中创建一个图片
        BufferedImage bufferedImage = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        //  得到图片
        Graphics2D graphics = (Graphics2D) bufferedImage.getGraphics();
        //  设置图片背景颜色
        graphics.setColor(Color.white);
        graphics.fillRect(0, 0, 80, 20);
        //  给图片写入数据
        graphics.setColor(Color.blue);
        graphics.setFont(new Font(null, Font.ITALIC,20));
        graphics.drawString(makeNum(),0,20);

        //  告诉浏览器, 这个请求的打开方式
        resp.setContentType("image/jpg");
        //  网站存在缓存, 不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache"); // no-Cache不缓存
        resp.setHeader("Pragma","no-cache");

        //  把图片写给浏览器
        ImageIO.write(bufferedImage,"jpg",resp.getOutputStream());
    }

    //  生成随机数
    private String makeNum() {
        Random random = new Random();
        String num = random.nextInt(9999) + "";   // 加入空格让生成随机数变成字符串
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 4- num.length(); i++) { // 保证字符串一定是四位(补零)
            sb.append("0");
        }
        String s = sb.toString() + num;
        return num;
    }


    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

4、实现重定向

一个web资源收到客户端请求之后, 它会通知客户端去访问另外一个web资源, 这个过程叫做重定向

常见常见:

用户登录

public class RedirectServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.sendRedirect("/resp/img");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

重定向与转发区别?

相同点:

页面发生跳转

不同点:

请求转发的时候URL不会产生变化，重定向的时候会发生变化。转发 307，重定向 302

1.7 HttpServletRequest

HttpServletRequest代表客户端的请求，用户通过Http协议访问服务器， Http请求的所有信息会被封装到HttpServletRequest中，通过HttpServletRequest获取客户端的所有信息

1、获取前端传递参数

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public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String[] hobby = req.getParameterValues("hobby");
        System.out.println("--------------------------");
        System.out.println(username);
        System.out.println(password);
        System.out.println(Arrays.toString(hobby));
        System.out.println("--------------------------");
        // 通过请求转发
//        req.getRequestDispatcher(req.getContextPath()+"/success.jsp").forward(req,resp);
        req.getRequestDispatcher("/success.jsp").forward(req,resp); // 请求转发不需要带项目名字
//        forward()该方法用于将请求从一个 Servlet 传递给另一个 Web 资源。在 Servlet 中，可以对请求做一个初步处理，然后通过调用这个方法，
//        将请求传递给其他资源进行响应。需要注意的是，该方法必须在响应提交给客户端之前被调用，否则将抛出 IllegalStateException 异常
    }
}

2、请求转发

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