JAVAWEB开发之Servlet3.0新特性的使用以及注解的详细使用和自定义注解的方法、动态代理的使用、利用动态代理实现细粒度的权限控制以及类加载和泛型反射

• @Override：限定重写父类的方法，该注解只能用于方法。
• @Deprecated：用于表示某个程序元素（类，方法等）已过时。
• @SuppressWarning：抑制编译器警告。

• 如何定义注解
• 如何反射注解，并根据反射的注解信息，决定如何去运行类。

package cn.itcast.annotation;import java.util.ArrayList;
import java.util.Date;
import java.util.List;@SuppressWarnings("all")
public class AnnotationDemo1 implements A {@Overridepublic String toString() {return super.toString();}//@Overridepublic void show() {}@Deprecatedpublic void print() {}public static void main(String[] args) {Date date = new Date();System.out.println(date.toLocaleString());int i = 10;List list = new ArrayList();}
}interface A {void show();
}

• 注解属性的作用：原来写在配置文件中的信息，可以通过注解的属性进行描述。
• Annotation 的属性声明方式：String name();
• 属性默认值声明方式：String name() default “xxx”;
• 特殊属性value：如果注解中有一个名称value的属性，那么使用注解时可以省略value=部分，如@MyAnnotation(“xxx")
• 特殊属性value[];

package cn.itcast.annotation;// 定义注解
public class AnnotationDemo2 {}@interface MyAnnotation1 {}@interface MyAnnotation {// 基本类型int show();float f();boolean b();// 字符串类型char c();// Class类型Class cl();// 枚举MyEnum m();// 注解类型MyAnnotation1 my1();// 以上类型的一维数组Class[] cls();String[] sts();
}enum MyEnum {A, B, C
}

package cn.itcast.annotation;import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;@MyAnnotation3
public class AnnotationDemo3 {@MyAnnotation3public void show(){}
}@Target({ElementType.TYPE,ElementType.METHOD})
@interface MyAnnotation3{//String st() default "abc";//int[] i();//String[] value();//int i();String value() default "hello";
}

3.提取Annotation信息

• JDK 5.0 在 java.lang.reflect 包下新增了 AnnotatedElement  接口, 该接口代表程序中可以接受注释的程序元素
• 当一个 Annotation 类型被定义为运行时 Annotation 后, 该注释才是运行时可见, 当 class 文件被载入时保存在 class 文件中的 Annotation 才会被虚拟机读取
• 程序可以调用 AnnotatedElement对象的如下方法来访问 Annotation 信息

money=5000

package cn.itcast.annotation.demo1;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface BankInfo {int maxMoney();
}

package cn.itcast.annotation.demo1;import java.lang.reflect.Method;//银行最大转账金额5000
@SuppressWarnings("all")
public class Bank {// name1向name2转账money元————使用配置文件完成public void account1(String name1, String name2, int money) {if (money > GlobalField.MONEY) {throw new RuntimeException("最大转账金额为5000");}System.out.println(name1 + "向" + name2 + "转账" + money + "元");}// name1向name2转账money元————使用注解完成@BankInfo(maxMoney = 5000)public void account(String name1, String name2, int money)throws NoSuchMethodException, SecurityException {// 1.获取当前方法的Method对象// 1.1获取当前类的Class对象Class clazz = this.getClass();// 1.2获取当前方法的Method对象Method method = clazz.getDeclaredMethod("account", String.class,String.class, int.class);// 判断当前方法上是否有BankInfo注解boolean flag = method.isAnnotationPresent(BankInfo.class);if (flag) {// 2.在Method类中有一个getAnnotation(Class annotationClass) 可以获取一个注解对象BankInfo bif = method.getAnnotation(BankInfo.class);// 3.通过注解对象来调用其属性int maxMoney = bif.maxMoney();if (money > maxMoney) {throw new RuntimeException("最大转账金额为5000");}System.out.println(name1 + "向" + name2 + "转账" + money + "元");}}
}

package cn.itcast.annotation.demo1;import java.util.ResourceBundle;public class GlobalField {public static final int MONEY = Integer.parseInt(ResourceBundle.getBundle("bank").getString("money"));
}

package cn.itcast.annotation.demo1;public class BankTest {public static void main(String[] args) throws NoSuchMethodException, SecurityException {Bank bank = new Bank();bank.account("张三", "李四", 1000);}
}

package cn.itcast.annotation.demo2;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface JdbcInfo {String driverClassName();String url();String username();String password();
}

package cn.itcast.annotation.demo2;import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.DriverManager;
import java.util.Arrays;public class JdbcUtils {public static Connection getConnection() throws Exception {String driverClassName = "com.mysql.jdbc.Driver";String url = "jdbc:mysql:///mydb1";String username = "root";String password = "root";// 1.加载驱动Class.forName(driverClassName);// 2.获取连接Connection con = DriverManager.getConnection(url, username, password);return con;}@JdbcInfo(driverClassName = "com.mysql.jdbc.Driver", url = "jdbc:mysql:///mydb1", username = "root", password = "root")public static Connection getConnectionByAnnotation(String[] args)throws Exception {System.out.println(Arrays.toString(args));// 得到当前方法上的注解JdbcInfoMethod method = JdbcUtils.class.getDeclaredMethod("getConnectionByAnnotation", String[].class);JdbcInfo jif = method.getAnnotation(JdbcInfo.class);String driverClassName = jif.driverClassName();String url = jif.url();String username = jif.username();String password = jif.password();// 1.加载驱动Class.forName(driverClassName);// 2.获取连接Connection con = DriverManager.getConnection(url, username, password);return con;}public static void main(String[] args) throws Exception {System.out.println(getConnectionByAnnotation(new String[] { "abc" }));}
}

关于映射的使用：简单示例如下：

package reflact;import java.lang.reflect.Method;import org.junit.Test;public class Demo {public static void main(String[] args) {System.out.println(args[0]);}@Testpublic void fun1() throws Exception{Method mainMethod=this.getClass().getDeclaredMethod("main", String[].class);//注意：如果获取的是静态方法，没有对象 所以第一个参数Object为nullmainMethod.invoke(null, (Object)(new String[]{"abc","def"}));}}

1.使用注解来替换配置文件

2.servlet3.0中的文件上传

3.servlet3.0中异步处理

package cn.itcast.web.filter;import java.io.IOException;import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;//@WebFilter("/*")
public class MyFilter implements Filter {@Overridepublic void destroy() {}@Overridepublic void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {System.out.println("my filter");chain.doFilter(request, response);}@Overridepublic void init(FilterConfig filterConfig) throws ServletException {}}

package cn.itcast.web.listener;import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;//@WebListener
public class MyListener implements ServletContextListener {@Overridepublic void contextDestroyed(ServletContextEvent arg0) {}@Overridepublic void contextInitialized(ServletContextEvent arg0) {System.out.println("myListener");}}

package cn.itcast.web.servlet;import java.io.IOException;import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;//@WebServlet(urlPatterns = { "/hello", "/h1" },initParams={@WebInitParam(name="username",value="tom"),@WebInitParam(name="encode",value="utf-8")})
public class MyServlet extends HttpServlet {@Overridepublic void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {doPost(req, resp);}@Overridepublic void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {System.out.println("hello servlet");// 获取初始化参数ServletConfig config = this.getServletConfig();String username = config.getInitParameter("username");System.out.println(username);}
}

package cn.itcast.web.servlet;import java.io.IOException;import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;@WebServlet("/upload")
@MultipartConfig
public class UploadServlet extends HttpServlet {@Overridepublic void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {doPost(req, resp);}@Overridepublic void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {req.setCharacterEncoding("utf-8");// 解决乱码Part part = req.getPart("f"); // 得到上传文件信息.//		req.getParts();// 获取上传文件名称String cd = part.getHeader("Content-Disposition");System.out.println(cd); // form-data; name="f";// filename="C:\Users\Administrator\Desktop\鎹曡幏.PNG"String filename = cd.substring(cd.lastIndexOf("\\") + 1,cd.length() - 1);System.out.println(filename);part.write("d:/upload/"+filename);// 完成文件上传.}}

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head><title>My JSP 'index.jsp' starting page</title>
</head><body><form action="${pageContext.request.contextPath}/upload" method="post"enctype="multipart/form-data"><input type="file" name="f"><input type="submit" value="上传"></form>
</body>
</html>

动态代理

1.代理模式

package cn.itcast.proxy;public class ProxyTest {public static void main(String[] args) {(new PersonProxy(new Person())).say("hello");}
}interface DoSomething {public void say(String word);
}class Person implements DoSomething {@Overridepublic void say(String word) {System.out.println(word);}}class PersonProxy implements DoSomething {private DoSomething dos;public PersonProxy(DoSomething dos) {this.dos = dos;}@Overridepublic void say(String word) {dos.say(word);}}

2.动态代理

动态代理案例1—实现编码过滤

package cn.itcast.proxy.demo;import java.io.IOException;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class EncodingFilter implements Filter {public void init(FilterConfig filterConfig) throws ServletException {}public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {// 1.强转final HttpServletRequest req = (HttpServletRequest) request;HttpServletResponse resp = (HttpServletResponse) response;// 2.操作// 创建一个req对象的代理对象reqProxyHttpServletRequest reqProxy = (HttpServletRequest) Proxy.newProxyInstance(req.getClass().getClassLoader(), req.getClass().getInterfaces(), new InvocationHandler() {public Object invoke(Object proxy, Method method,Object[] args) throws Throwable {// 1.得到方法名称String methodName = method.getName();if ("getParameter".equals(methodName)) {String param = req.getParameter((String) (args[0]));return new String(param.getBytes("iso8859-1"),"utf-8");} else {// 不是getParameter方法，就执行其原来操作.return method.invoke(req, args);}}});// 3.放行chain.doFilter(reqProxy, resp);}public void destroy() {}}

        <filter><filter-name>encodingFilter</filter-name><filter-class>cn.itcast.proxy.demo.EncodingFilter</filter-class></filter><filter-mapping><filter-name>encodingFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping>

动态代理案例二—动态代理+注解实现的细粒度的权限控制

create table users(id int primary key auto_increment,username varchar(40),password varchar(40));insert into users values(null,'aaa','111');insert into users values(null,'bbb','111');insert into users values(null,'ccc','111');create table privileges(id int primary key auto_increment,name varchar(40));insert into privileges values(null,'添加图书');insert into privileges values(null,'修改图书');insert into privileges values(null,'查看图书');insert into privileges values(null,'删除图书');多对多表关系create table userprivilege(user_id int ,privilege_id int,foreign key(user_id) references users(id),foreign key(privilege_id) references privileges(id),primary key(user_id,privilege_id));insert into userprivilege values(1,1);

                ......

package cn.itcast.utils;import java.sql.Connection;
import java.sql.SQLException;import javax.sql.DataSource;import com.mchange.v2.c3p0.ComboPooledDataSource;public class DataSourceUtils {private static ComboPooledDataSource cpds = new ComboPooledDataSource();public static Connection getConnection() throws SQLException {return cpds.getConnection();}public static DataSource getDataSource() {return cpds;}}

package cn.itcast.book.annotation;import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@Inherited
public @interface BookInfo {String value();// 即权限名称
}

package cn.itcast.book.dao;import java.sql.SQLException;import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;import cn.itcast.book.domain.User;
import cn.itcast.utils.DataSourceUtils;public class UserDao {// 登录操作public User findUserByUserNameAndPassword(String username, String password)throws SQLException {String sql = "select * from users where username=? and password=?";QueryRunner runner = new QueryRunner(DataSourceUtils.getDataSource());return runner.query(sql, new BeanHandler<User>(User.class), username,password);}
}

package cn.itcast.book.domain;public class User {private int id;private String username;private String password;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}}

package cn.itcast.book.service;import cn.itcast.book.annotation.BookInfo;
import cn.itcast.book.domain.User;public interface BookService {@BookInfo("添加图书")public void addBook(User user) throws Exception;@BookInfo("修改图书")public void updateBook(User user) throws Exception;@BookInfo("删除图书")public void deleteBook(User user) throws Exception;public void searchBook(User user) throws Exception;
}

package cn.itcast.book.service;import cn.itcast.book.domain.User;public class BookServiceImpl implements BookService {public void addBook(User user) throws Exception {System.out.println("book add.");}public void updateBook(User user) throws Exception {System.out.println("book update");}public void deleteBook(User user) throws Exception {System.out.println("book delete");}public void searchBook(User user) throws Exception {System.out.println("book search");}}

package cn.itcast.book.service;import java.sql.SQLException;import cn.itcast.book.dao.UserDao;
import cn.itcast.book.domain.User;public class UserService {public User login(String username, String password) throws SQLException {return new UserDao().findUserByUserNameAndPassword(username, password);}
}

package cn.itcast.book;import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.List;import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.ColumnListHandler;import cn.itcast.book.annotation.BookInfo;
import cn.itcast.book.domain.User;
import cn.itcast.book.service.BookService;
import cn.itcast.book.service.BookServiceImpl;
import cn.itcast.utils.DataSourceUtils;public class BookServiceFactory {private static BookService service = new BookServiceImpl();public static BookService getInstance() {BookService proxy = (BookService) Proxy.newProxyInstance(service.getClass().getClassLoader(), service.getClass().getInterfaces(), new InvocationHandler() {@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {// 真实行为访问前--判断用户是否有权限执行当前行为boolean flag = method.isAnnotationPresent(BookInfo.class);if (!flag) {// 不需要权限return method.invoke(service, args);}// 1.得到Method方法要想访问需要的权限BookInfo bif = method.getAnnotation(BookInfo.class);String pname = bif.value();System.out.println("需要的权限是: " + pname);// 2.得到当前用户User user = (User) args[0];if (user == null) {throw new RuntimeException("没有登录，请登录后操作");}// 3.从数据库中查询出当前用户所具有的的所有权限名称String sql = "SELECT privileges.name FROM users,PRIVILEGES,userprivilege WHERE users.id=userprivilege.user_id AND privileges.id=userprivilege.privilege_id AND users.id=?";QueryRunner runner = new QueryRunner(DataSourceUtils.getDataSource());List<Object> pnames = runner.query(sql,new ColumnListHandler(), user.getId());System.out.println("当前用户是" + user.getUsername() + ",它具有的权限是:"+ pnames);if (pnames.contains(pname)) {Object obj = method.invoke(service, args);return obj;} else {throw new RuntimeException("权限不足");}}});return proxy;}
}

package cn.itcast.book.servlet;import java.io.IOException;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import cn.itcast.book.BookServiceFactory;
import cn.itcast.book.domain.User;
import cn.itcast.book.service.BookService;public class BookServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String method = request.getParameter("method");if ("add".equals(method)) {add(request, response);} else if ("update".equals(method)) {update(request, response);} else if ("delete".equals(method)) {delete(request, response);} else if ("search".equals(method)) {search(request, response);}}public void add(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {BookService service = BookServiceFactory.getInstance();User user = (User) request.getSession().getAttribute("user");try {service.addBook(user);} catch (Exception e) {e.printStackTrace();}}public void update(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {BookService service = BookServiceFactory.getInstance();User user = (User) request.getSession().getAttribute("user");try {service.updateBook(user);} catch (Exception e) {e.printStackTrace();}}public void delete(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {BookService service = BookServiceFactory.getInstance();User user = (User) request.getSession().getAttribute("user");try {service.deleteBook(user);} catch (Exception e) {e.printStackTrace();}}public void search(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {BookService service = BookServiceFactory.getInstance();User user = (User) request.getSession().getAttribute("user");try {service.searchBook(user);} catch (Exception e) {e.printStackTrace();}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

package cn.itcast.book.servlet;import java.io.IOException;
import java.sql.SQLException;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import cn.itcast.book.domain.User;
import cn.itcast.book.service.UserService;public class LoginServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//1.得到请求参数String username=request.getParameter("username");String password=request.getParameter("password");//2.调用service完成登录操作UserService service=new UserService();try {User user=service.login(username, password);if(user!=null){request.getSession().setAttribute("user", user);response.sendRedirect(request.getContextPath()+"/book.jsp");return;}} catch (SQLException e) {e.printStackTrace();}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'login.jsp' starting page</title>
</head><body>当前用户:${user.username}<br><hr><a href="${pageContext.request.contextPath}/book?method=add">bookadd</a><br><a href="${pageContext.request.contextPath}/book?method=update">bookupdate</a><br><a href="${pageContext.request.contextPath}/book?method=delete">bookdelete</a><br><a href="${pageContext.request.contextPath}/book?method=search">booksearch</a><br>
</body>
</html>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'login.jsp' starting page</title>
</head><body><form action="${pageContext.request.contextPath}/login" method="get">username:<input type="text" name="username"><br>password:<input type="password" name="password"><br> <inputtype="submit" value="登录"></form>
</body>
</html>

类加载器

• 类加载器负责将 .class 文件(可能在磁盘上, 也可能在网络上) 加载到内存中, 并为之生成对应的 java.lang.Class 对象
• 当 JVM 启动时，会形成由三个类加载器组成的初始类加载器层次结构： 

泛型反射