解决服务端接收数据乱码问题。服务器默认采用 ISO8859-1 编码响应内容。

// 1req.setCharacterEncoding("utf-8");// 2    byte[] bytes = req.getParameter("username").getBytes("iso-8859-1");    System.out.println("username:" + new String(bytes,0,bytes.length,"utf-8"));

        解决服务端发送到客户端数据乱码问题。

// 1 text/html,响应数据类型;     resp.setContentType("text/html;charset=utf8;");     // 2     resp.setCharacterEncoding("utf-8");     resp.setHeader("Content-type","text/html;charset=utf8");

        单元测试。

        src 同级目录创建 test 文件夹，右键 -> Mark Directory as ->Sources Root，文件名采用测试的模块名 + Test。

        转发。转发的作用在服务器端，将请求发送给服务器上的其他资源，以共同完成一次请求的处理。使用forward跳转时，是在服务器内部跳转，地址栏不发生变化，属于同一次请求。

request.getRequestDispatcher(“/目标URL-pattern”).forward(request, response);// 存数据request.setAttribute(key,value);// 取数据request.getAttribute(key);

        重定向。重定向作用在客户端，客户端将请求发送给服务器后，服务器响应给客户端一个新的请求地址，客户端重新发送新请求。

        重定向可以指向任何的资源，包括当前应用程序中的其他资源、同一个站点上的其他应用程序中的资源、其他站点的资源。

response.sendRedirect(“目标URI”);// 带数据response.sendRedirect(“目标URI?username=tom&ps=123”);// 接收数据request.getParameter(“username”);

        servlet 用户管理系统。

        目录结构。

public class AddUserServlet extends HttpServlet {    private IUserService userService = new UserServiceImpl();    @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.setContentType("text/html;charset=utf8");        String username = req.getParameter("username");        String password = req.getParameter("password");        String age = req.getParameter("age");        String sex = req.getParameter("sex");        User user = new User();        user.setUsername(username);        user.setPassword(password);        user.setAge(Integer.valueOf(age));        user.setSex(Integer.valueOf(sex));        int i = userService.AddUser(user);        if (i == 0) {            resp.getWriter().write("添加失败");        } else {            resp.getWriter().write("添加成功");            resp.getWriter().write("查询所有用户");        }    }}public class DeleteUserServlet extends HttpServlet {    private IUserService userService = new UserServiceImpl();    @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.setContentType("text/html;charset=utf8");        String username = req.getParameter("username");        int i = userService.DeleteUser(username);        if (i == 0) {            resp.getWriter().write("删除失败");        } else {            resp.getWriter().write("删除成功");            resp.getWriter().write("查询所有用户");        }    }}public class GetUserListServlet extends HttpServlet {    private IUserService userService = new UserServiceImpl();    @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.setContentType("text/html;charset=utf8");        System.out.println("查询所有的用户:" + req);        List userList = userService.getUserList();        // 转发数据        req.setAttribute("userList",userList);        // 转发对象        req.getRequestDispatcher("ViewUserServlet").forward(req,resp);        // 重定向 最好不带参数        resp.sendRedirect("ViewUserServlet?username=zs&password=123");        resp.sendRedirect("http://www.baidu.com");    }}public class LoginUserServlet extends HttpServlet {    private IUserService userService = new UserServiceImpl();    @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.setContentType("text/html;charset=utf8");        String username = req.getParameter("username");        String password = req.getParameter("password");        User user = userService.login(username, password);        if (user == null) {            resp.getWriter().write("用户名或密码错误..");        } else {            resp.getWriter().write("欢迎【" + req.getRemoteAddr() + username + "】登陆");            resp.getWriter().write("查询所有用户");        }    }}public class SelectUserServlet extends HttpServlet {    private IUserService userService = new UserServiceImpl();    @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.setContentType("text/html;charset=utf8");        System.out.println("查询所有的用户:" + req);        String username = req.getParameter("username");        User user = userService.SelectUser(username);        StringBuffer buffer = new StringBuffer();        buffer.append("");        buffer.append("");        buffer.append("

public interface IUserDao {    public User login(String username);    public ListgetUserList();    public int AddUser(User user);    public int DeleteUser(String name);    public int UpdateUser(User user);    public User SelectUser(String name);}public class UserDaoImpl implements IUserDao {    @Override    public User login(String username) {        String sql = "select * from t_user where username = ?";        List users = DaoUtils.commonQuery(sql, User.class, username);        if (users.isEmpty()) {            return null;        }        return users.get(0);    }    @Override    public ListgetUserList() {        return DaoUtils.commonQuery("select * from t_user", User.class);    }    @Override    public int AddUser(User user) {        List userList = getUserList();        // 存在同名        for (User subUser: userList) {            if (subUser.getUsername().equals(user.getUsername())) {                return 0;            }        }        String sql = "insert into t_user(username, password, age, sex) value(?, ?, ?, ?)";        int i = DaoUtils.commonUpdate(sql, user.getUsername(),user.getPassword(), user.getAge(),user.getSex());        return i;    }    @Override    public int DeleteUser(String username) {        String sql = "delete  from t_user where username = ?";        int i = DaoUtils.commonUpdate(sql, username);        return i;    }    @Override    public int UpdateUser(User user) {        String sql = "update t_user set password=?,age=?,sex=? where username = ?";        int i = DaoUtils.commonUpdate(sql,user.getPassword(),user.getAge(),user.getSex(),user.getUsername());        return i;    }    public User SelectUser(String name) {        List users = DaoUtils.commonQuery("select * from t_user where username = ?", User.class, name);        if (users.isEmpty()) {            return null;        }        return users.get(0);    }}

@Datapublic class User {    private Integer id;    private String username;    private String password;    private Integer age;    private Integer sex;}

public interface IUserService {    public User login(String username, String password);    public ListgetUserList();    public int AddUser(User user);    public int DeleteUser(String name);    public int UpdateUser(User user);    public User SelectUser(String name);}public class UserServiceImpl implements IUserService {    private IUserDao userDao = new UserDaoImpl();    @Override    public User login(String username, String password) {        User user = userDao.login(username);        if (user == null) {            System.out.println("用户名或密码错误");            return null;        }        if (!user.getPassword().equals(password)) {            System.out.println("用户名或密码错误");            return null;        }        return user;    }    @Override    public ListgetUserList() {        return userDao.getUserList();    }    public int AddUser(User user) {        return userDao.AddUser(user);    }    public int DeleteUser(String name) {        return userDao.DeleteUser(name);    }    public int UpdateUser(User user) {        return userDao.UpdateUser(user);    }    public User SelectUser(String name) {        return userDao.SelectUser(name);    }}

public class DaoUtils {    // 更改    public static int commonUpdate(String sql, Object ...args) {        Connection connection = DBUtils.getConnection();        PreparedStatement prst = null;        try {            prst = connection.prepareStatement(sql);            if (args != null && args.length > 0) {                for (int i = 0; i < args.length; i ++) {                    prst.setObject(i + 1,args[i]);                }            }            return prst.executeUpdate();        } catch (SQLException e) {            e.printStackTrace();        } finally {            DBUtils.close(prst);        }        return 0;    }    // 查询    public static ListcommonQuery(String sql, Class cls, Object ...args) {        Connection connection = DBUtils.getConnection();        PreparedStatement prst = null;        ResultSet resultSet = null;        List list = new ArrayList<>();        try {            prst = connection.prepareStatement(sql);            if (args != null && args.length > 0) {                for (int i = 0; i < args.length; i ++) {                    prst.setObject(i + 1,args[i]);                }            }            resultSet = prst.executeQuery();            while (resultSet.next()) {                T t = cls.newInstance();                Field[] fields = cls.getDeclaredFields();                for (Field field: fields) {                    // 设置动态给属性赋值权限                    field.setAccessible(true);                    Object value = null;                    try {                        value = resultSet.getObject(field.getName());                    } catch (SQLException e) {                        // 出现实体字段和数据库字段不一致                        String columnName = DBUtils.getProperties().getProperty(field.getName());                        value = resultSet.getObject(columnName);                    }                    field.set(t, value);                }                list.add(t);            }        } catch (SQLException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        } catch (InstantiationException e) {            e.printStackTrace();        } finally {            DBUtils.close(resultSet, prst);        }        return list;    }}

public class DBUtils {    private static DataSource dataSource = null;    private static Properties properties = new Properties();    private static ThreadLocal threadLocal = new ThreadLocal<>();    static {        try {            properties.load(DBUtils.class.getClassLoader().getResourceAsStream("jdbc.properties"));            dataSource = DruidDataSourceFactory.createDataSource(properties);        } catch (IOException e) {            e.printStackTrace();        } catch (Exception e) {            e.printStackTrace();        }    }    public static Properties getProperties() {        return properties;    }    public static Connection getConnection() {        Connection connection = threadLocal.get();        if (connection == null) {            try {                connection = dataSource.getConnection();                threadLocal.set(connection);            } catch (SQLException e) {                e.printStackTrace();            }        }        return connection;    }    public static void close(AutoCloseable ...args) {        for (AutoCloseable obj: args) {            if (obj != null) {                try {                    obj.close();                } catch (Exception e) {                    e.printStackTrace();                }            }        }    }}

# jdbc.properties#连接设置driverClassName=com.mysql.cj.jdbc.Driverurl=jdbc:mysql://localhost:3306/mydb1?characterEncoding=utf-8username=rootpassword=Liu01234#初始化可连接数量，实际项目时要设置更大值initialSize=100#最大连接数量maxActive=500#最小空闲连接，当空闲连接小于此值时会开辟新当空间，直到最大连接数量minIdle=50#超时等待时间以毫秒为单位 1000等于1秒maxWait=5000

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns="http://java.sun.com/xml/ns/javaee"           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"           xsi:schemaLocation="http://java.sun.com/xml/ns/javaee      http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"           version="2.5">        <servlet>        <servlet-name>LoginUserServletservlet-name>        <servlet-class>com.baidu.day.test1.controller.LoginUserServletservlet-class>    servlet>    <servlet-mapping>        <servlet-name>LoginUserServletservlet-name>        <url-pattern>/LoginUserServleturl-pattern>    servlet-mapping>        <servlet>        <servlet-name>GetUserListServletservlet-name>        <servlet-class>com.baidu.day.test1.controller.GetUserListServletservlet-class>    servlet>    <servlet-mapping>        <servlet-name>GetUserListServletservlet-name>        <url-pattern>/GetUserListServleturl-pattern>    servlet-mapping>        <servlet>        <servlet-name>ViewUserServletservlet-name>        <servlet-class>com.baidu.day.test1.controller.ViewUserServletservlet-class>    servlet>    <servlet-mapping>        <servlet-name>ViewUserServletservlet-name>        <url-pattern>/ViewUserServleturl-pattern>    servlet-mapping>        <servlet>        <servlet-name>AddUserServletservlet-name>        <servlet-class>com.baidu.day.test1.controller.AddUserServletservlet-class>    servlet>    <servlet-mapping>        <servlet-name>AddUserServletservlet-name>        <url-pattern>/AddUserServleturl-pattern>    servlet-mapping>        <servlet>        <servlet-name>DeleteUserServletservlet-name>        <servlet-class>com.baidu.day.test1.controller.DeleteUserServletservlet-class>    servlet>    <servlet-mapping>        <servlet-name>DeleteUserServletservlet-name>        <url-pattern>/DeleteUserServleturl-pattern>    servlet-mapping>        <servlet>        <servlet-name>UpdateUserServletservlet-name>        <servlet-class>com.baidu.day.test1.controller.UpdateUserServletservlet-class>    servlet>    <servlet-mapping>        <servlet-name>UpdateUserServletservlet-name>        <url-pattern>/UpdateUserServleturl-pattern>    servlet-mapping>    <servlet>        <servlet-name>SelectUserServletservlet-name>        <servlet-class>com.baidu.day.test1.controller.SelectUserServletservlet-class>    servlet>    <servlet-mapping>        <servlet-name>SelectUserServletservlet-name>        <url-pattern>/SelectUserServleturl-pattern>    servlet-mapping>web-app>

<%-- index.jsp --%><%@ page contentType="text/html;charset=UTF-8" language="java" %><html>  <head>    <title>$Title$title>  head>  <body>  <form method="post" action="LoginUserServlet">    username:<input type="text" name="username" value="zs"><br><br>    password:<input type="text" name="password" value="123"><br><br>    <input type="submit" value="登陆">  form>  <br><br>  <form method="post" action="AddUserServlet">    username:<input type="text" name="username" value="zs"><br><br>    password:<input type="text" name="password" value="123"><br><br>    age:<input type="text" name="age" value="12"><br><br>    sex:<input type="text" name="sex" value="1"><br><br>    <input type="submit" value="添加用户">  form>  <br><br>  <form method="post" action="DeleteUserServlet">    username:<input type="text" name="username" value="zs"><br><br>    <input type="submit" value="删除用户">  form>  <br><br>  <form method="post" action="SelectUserServlet">    username:<input type="text" name="username" value="zs"><br><br>    <input type="submit" value="查询用户">  form>  <br><br>  <form method="post" action="UpdateUserServlet">    username:<input type="text" name="username" value="zs"><br><br>    password:<input type="text" name="password" value="123"><br><br>    age:<input type="text" name="age" value="12"><br><br>    sex:<input type="text" name="sex" value="1"><br><br>    <input type="submit" value="修改用户">  form>  <br><br>  body>html>