Java基础——Maven

Maven

• 搭建一个项目需要考虑哪些内容？
  
• Maven是一个Java项目管理和构建工具

1. 标准化项目结构
2. 标准化构建流程
3. 依赖管理等

• 标准的Maven项目结构
  
• 普通java项目的描述文件
  

groupId与artifactId被称为项目坐标，作用就是定位！
groupId一般被设置为包名，而包名一般使用“域名+其他名称”，如org.apache，apache代表公司名
artifactId是唯一的，一般设为模块名；即使项目分为多模块，也能唯一定位子模块

创建Maven项目

• 借助IDEA工具可以创建Maven项目，一般选择quickstart
• 第一次创建会下载一些插件
• 声明一个依赖项，Maven可以自动下载并导入相关jar包

依赖管理

• Maven为我们管理了复杂的依赖包
• Maven设置的依赖关系有以下几种：
  
• Maven从何处下载这些依赖？
  
• Maven的中央仓库
• 最重要的还是配置文件pom.xml，包含项目属性、依赖、插件等信息；下面是一个Maven项目的配置文件

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0modelVersion>

	<groupId>com.feiyangedu.samplegroupId>
	<artifactId>hellodepartifactId>
	<version>0.0.1-SNAPSHOTversion>
	<packaging>jarpackaging>

	<properties>
		<project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
		<java.version>1.8java.version>
		<maven.compiler.source>1.8maven.compiler.source>
		<maven.compiler.target>1.8maven.compiler.target>
	properties>

	<dependencies>
		<dependency>
			<groupId>commons-logginggroupId>
			<artifactId>commons-loggingartifactId>
			<version>1.2version>
		dependency>
		<dependency>
			<groupId>org.apache.logging.log4jgroupId>
			<artifactId>log4j-jclartifactId>
			<version>2.8.2version>
			<scope>runtimescope>
		dependency>
		<dependency>
			<groupId>org.apache.logging.log4jgroupId>
			<artifactId>log4j-coreartifactId>
			<version>2.8.2version>
			<scope>runtimescope>
		dependency>
		<dependency>
			<groupId>junitgroupId>
			<artifactId>junitartifactId>
			<version>4.12version>
			<scope>testscope>
		dependency>
	dependencies>
project>

• 可以给Maven配置镜像，加速下载，需要在用户目录的.m2文件夹下新建settings
  
  

Maven执行流程

• Maven的生命周期由一系列阶段（phase）构成
  
• 使用Maven构建项目就是执行指定的Phase
• 执行一个Phase其实执行了一系列阶段，只不过到此为止，例如：
  
• 执行一个Phase又会触发绑定的一个或多个Goal，Goal是最小执行单元

结合命令行使用Maven

• 下载Maven管理工具
• 将bin/目录添加至环境变量，也可以创建M2_HOME环境变量
• 使用mvn命令查看是否安装成功
• 接着便可以使用命令行编译和测试项目了

mvn clean compile	// 可能需要将JDK的目录设为%JAVA_HOME%并添加至path，上移
mvn test 	// 执行项目测试
mvn clean package	// 最常用，打成jar包		不会打包依赖的jar

• Maven实际上是通过插件执行各phase
  
• 常用的插件
  
• 如果提供的插件不满足要求，可以自己引入插件，常见的有：

1. maven-shade-plugin：打包所有依赖包生成可执行jar
2. cobertura-maven-plugin：生成单元测试覆盖率报告
3. findbugs-maven-plugin：对java源码进行静态分析

• 我们只需要将插件的配置加入到项目配置文件即可，如下所示：

4. 打包依赖文件，生成可执行jar包

// 使用maven-shade-plugin，生成可执行jar包
// 网页搜索maven shade plugin executable jar
<plugins>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-shade-plugin</artifactId>
    <version>3.2.2</version>
    <executions>
      <execution>
        <phase>package</phase>
        <goals>
          <goal>shade</goal>
        </goals>
        <configuration>
          <transformers>
            <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
              <mainClass>org.sonatype.haven.HavenCli</mainClass>
            </transformer>
          </transformers>
        </configuration>
      </execution>
    </executions>
  </plugin>
</plugins>
// 将上面的配置放在 中
// 项目文件夹下使用命令：mvn clean package即可将相关依赖也打包
// 注意区分依赖jar包和插件

2. 使用cobertura生成单元测试覆盖率

// 网页搜索 cobertura maven plugin usage
// 加入到pom.xml
<plugin>
	<groupId>org.codehaus.mojogroupId>
	<artifactId>cobertura-maven-pluginartifactId>
	<version>2.7version>
plugin>
// 貌似这些东西都放在<build>中才行

// 编写个除main之外的方法
public class App {
     
    public static void main(String[] args) {
     
        Log log = LogFactory.getLog(App.class);
        log.info("Hello, world!");
    }

    public int sum(int ... ns) {
     
        int x = 0;
        for (int n:ns){
     
            x += n;
        }
        return x;
    }
}
// 编写测试
import org.junit.Test;
import static org.junit.Assert.*;
public class AppTest {
     
    @Test
    public void testApp() {
     
//        assertTrue(true);
       // App.main(null); // 未测试到
        assertEquals(6,new App().sum(1,2,3));
    }
}
// 命令行：mvn cobertura:cobertura
// 这是一个Goal操作，可以直接执行

• 在target/site中可以查看index.html页面报告
  
• 插件的配置和用法需要参考官方文档

模块管理

• 将一个大项目拆分成模块是降低复杂度的有效方法
• Maven可以有效管理多个模块，IDEA创建多模块：

// 新建Maven项目（基模块）mavenFirst，项目中：New——Module——Maven，填入子模块的标识信息即可
// 也可以通过 File——Project Structure——Modules——New Module创建
// 子模块配置继承父模块：
<parent>
    <artifactId>mavenFirstartifactId>
    <groupId>xyz.roykungroupId>
    <version>1.0-SNAPSHOTversion>
parent>
// 子模块一般不需再设置groupId，和父模块一致即可！
// 继承父模块后，可以使用其下载好的依赖；也可将公共配置均放置在父模块

// 在父模块中设置<modules>，可以在编译项目的时候自动解析出各模块，生成文件也存放在各自的target
<modules>
    <module>greetingmodule>
modules>

• 在父模块下使用mvn clean compile查看效果
  

网络编程

• 这部分需要计算机网络的基础知识，包括TCP/IP协议，OSI模型等，这里不介绍

TCP编程

• 网络中进程间如何通信？操作系统抽象出socket（套接字），用来对接通信的地址和应用的进程
  
• 可以将socket理解为IP地址+端口号
• 进行socket编程分为客户端和服务器端
  
  
• 客户端

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.nio.charset.StandardCharsets;

/**
 * Java网络编程
 */
public class TCPClient {
     
    public static void main(String[] args) throws IOException {
     
        InetAddress addr = InetAddress.getLoopbackAddress(); // "127.0.0.1"
        try (Socket sock = new Socket(addr, 9090)) {
         // 客户端套接字
            try (BufferedReader reader = new BufferedReader(
                    new InputStreamReader(sock.getInputStream(), StandardCharsets.UTF_8))) {
     
                try (BufferedWriter writer = new BufferedWriter(// Filter包装还记得吗？
                        new OutputStreamWriter(sock.getOutputStream(), StandardCharsets.UTF_8))) {
     
                    writer.write("time\n");
                    writer.flush();	// 强制输出缓冲区
                    String resp = reader.readLine();    // 读取服务器返回信息
                    System.out.println("Response: " + resp);
                }
            }
        }
    }
}

• 服务器端

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
import java.time.LocalDateTime;

public class TCPServer {
     
    public static void main(String[] args) throws Exception {
     
        ServerSocket ss = new ServerSocket(9090);   // 服务器端套接字，监听端口信息
        System.out.println("TCP server ready.");
        Socket sock = ss.accept();  // 接收连接（套上了）
        try (BufferedReader reader = new BufferedReader(// 这个sock是服务器的
                new InputStreamReader(sock.getInputStream(), StandardCharsets.UTF_8))) {
     
            try (BufferedWriter writer = new BufferedWriter(
                    new OutputStreamWriter(sock.getOutputStream(), StandardCharsets.UTF_8))) {
     
                String cmd = reader.readLine();
                if ("time".equals(cmd)) {
     
                    writer.write(LocalDateTime.now().toString() + "\n");
                    writer.flush();
                } else {
     
                    writer.write("Sorry?\n");
                    writer.flush();
                }
            }
        }
        sock.close();
        ss.close();
    }
}

• 先启动服务器端程序开启监听，再启动客户端程序即可得到Response

TCP多线程编程

• 一个ServerSocket可以与多个客户端建立联系
• 服务器端使用无限循环建立连接：
  
• 客户端

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.nio.charset.StandardCharsets;

public class TCPClient {
     
	public static void main(String[] args) throws Exception {
     
		InetAddress addr = InetAddress.getByName("localhost");
		try (Socket sock = new Socket(addr, 9090)) {
     
			try (BufferedReader reader = new BufferedReader(
					new InputStreamReader(sock.getInputStream(), StandardCharsets.UTF_8))) {
     
				try (BufferedWriter writer = new BufferedWriter(
						new OutputStreamWriter(sock.getOutputStream(), StandardCharsets.UTF_8))) {
     
					writer.write("time\n");
					writer.flush();
					String resp = reader.readLine();
					System.out.println("Response: " + resp);
					Thread.sleep(1000);
					writer.write("q\n");
					writer.flush();
					resp = reader.readLine();
					System.out.println("Response: " + resp);
				}
			}
		}
	}
}

• 服务器端

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
import java.time.LocalDateTime;

public class TCPServer {
     
	public static void main(String[] args) throws Exception {
     
		@SuppressWarnings("resource")
		ServerSocket ss = new ServerSocket(9090);
		System.out.println("TCP server ready.");
		for (;;) {
     
			Socket sock = ss.accept();
			System.out.println("Accept from " + sock.getRemoteSocketAddress());
			TimeHandler handler = new TimeHandler(sock);// 开启一个新的线程
			handler.start();
		}
	}
}

class TimeHandler extends Thread {
     
	Socket sock;

	TimeHandler(Socket sock) {
     
		this.sock = sock;
	}
	@Override
	public void run() {
     
		try (BufferedReader reader = new BufferedReader(
				new InputStreamReader(sock.getInputStream(), StandardCharsets.UTF_8))) {
     
			try (BufferedWriter writer = new BufferedWriter(
					new OutputStreamWriter(sock.getOutputStream(), StandardCharsets.UTF_8))) {
     
				for (;;) {
     
					String cmd = reader.readLine();
					if ("q".equals(cmd)) {
     
						writer.write("bye!\n");
						writer.flush();
						break;
					} else if ("time".equals(cmd)) {
     
						writer.write(LocalDateTime.now().toString() + "\n");
						writer.flush();
					} else {
     
						writer.write("Sorry?\n");
						writer.flush();
					}
				}
			}
		} catch (IOException e) {
     
			e.printStackTrace();
		} finally {
     
			try {
     
				this.sock.close();
			} catch (IOException e) {
     
				e.printStackTrace();
			}
		}
	}
}

• 使用线程池可以提高效率

UDP编程

• 不需要建立连接，可以直接收发数据
• 客户端：
  
• 服务器端：
  
• 使用DatagramSocket建立套接字
• 使用receive/send方法发送接收数据
• 没有IO流接口

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.nio.charset.StandardCharsets;

public class UDPClient {
     
    public static void main(String[] args) throws Exception {
     
        InetAddress addr = InetAddress.getLoopbackAddress();
        try (DatagramSocket sock = new DatagramSocket()) {
     
            sock.connect(addr, 9090);	// 并不建立连接
            byte[] data = "time".getBytes(StandardCharsets.UTF_8);
            DatagramPacket packet = new DatagramPacket(data, data.length);
            sock.send(packet);
            System.out.println("Data was sent.");
            Thread.sleep(1000);
            byte[] buffer = new byte[1024];
            DatagramPacket resp = new DatagramPacket(buffer, buffer.length);
            sock.receive(resp);
            byte[] respData = resp.getData();
            String respText = new String(respData, 0, resp.getLength(), StandardCharsets.UTF_8);
            System.out.println("Response: " + respText);
        }
    }
}

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.nio.charset.StandardCharsets;
import java.time.LocalDateTime;

public class UDPServer {
     
    public static void main(String[] args) throws Exception {
     
        @SuppressWarnings("resource")
        DatagramSocket ds = new DatagramSocket(9090);// 服务器端监听
        System.out.println("UDP server ready.");
        for (;;) {
     
            // receive:
            byte[] buffer = new byte[1024];
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
            ds.receive(packet);     // 接收客户端信息
            byte[] data = packet.getData();
            String s = new String(data, StandardCharsets.UTF_8);
            System.out.println("Packet received from: " + packet.getSocketAddress() + " " + s);
            // send:
            String resp = LocalDateTime.now().toString();
            packet.setData(resp.getBytes(StandardCharsets.UTF_8));
            ds.send(packet);    // 发送
        }
    }
}

邮件收发

发送邮件

• 发送邮件就是从MUA到MDA的过程
• 从MUA到MTA发送email使用的协议是SMTP
• 端口号25，加密端口465/587
• 使用JavaMail API发送邮件：
  

1. 使用Maven引入Javamail依赖
2. 确定SMTP服务器信息：域名/端口/使用明文/SSL
3. 调用API发送（无序关心底层socket连接）
4. 设置debug模式可以排查错误

import java.util.Properties;
import javax.mail.Authenticator;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class SendMail {
     

	final String smtpHost;
	final String username;
	final String password;
	final boolean debug;

	public SendMail(String smtpHost, String username, String password) {
     
		// 这里填入你自己的某个邮箱信息
		//使用哪个邮箱就用哪个的SMTP服务器，有的服务器可能需要开启一下SMTP服务
		this.smtpHost = smtpHost;
		this.username = username;
		this.password = password;
		this.debug = true;
	}

	public static void main(String[] args) throws Exception {
     
		// 发送者信息
		SendMail sender = new SendMail("smtp.qq.com", "[email protected]", "xxxxxx");
		Session session = sender.createTLSSession();
		Message message = createTextMessage(session, "[email protected]", "[email protected]", "Java邮件测试",
				"Hello, 这是一封javamail测试邮件！");
		Transport.send(message);
	}

	Session createSSLSession() {
     
		Properties props = new Properties();
		props.put("mail.smtp.host", this.smtpHost); // SMTP主机名
		props.put("mail.smtp.port", "465"); // 主机端口号
		props.put("mail.smtp.auth", "true"); // 是否需要用户认证
		// 启动SSL:
		props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
		props.put("mail.smtp.socketFactory.port", "465");
		Session session = Session.getInstance(props, new Authenticator() {
     
			// 用户名+口令认证:
			protected PasswordAuthentication getPasswordAuthentication() {
     
				return new PasswordAuthentication(SendMail.this.username, SendMail.this.password);
			}
		});
		session.setDebug(this.debug); // 显示调试信息
		return session;
	}

	Session createTLSSession() {
     
		Properties props = new Properties();
		props.put("mail.smtp.host", this.smtpHost); // SMTP主机名
		props.put("mail.smtp.port", "587"); // 主机端口号
		props.put("mail.smtp.auth", "true"); // 是否需要用户认证
		props.put("mail.smtp.starttls.enable", "true"); // 启用TLS加密
		Session session = Session.getInstance(props, new Authenticator() {
     
			protected PasswordAuthentication getPasswordAuthentication() {
     
				return new PasswordAuthentication(SendMail.this.username, SendMail.this.password);
			}
		});
		session.setDebug(this.debug); // 显示调试信息
		return session;
	}

	Session createInsecureSession(String host, String username, String password) {
     
		Properties props = new Properties();
		props.put("mail.smtp.host", this.smtpHost); // SMTP主机名
		props.put("mail.smtp.port", "25"); // 主机端口号
		props.put("mail.smtp.auth", "true"); // 是否需要用户认证
		Session session = Session.getInstance(props, new Authenticator() {
     
			protected PasswordAuthentication getPasswordAuthentication() {
     
				return new PasswordAuthentication(SendMail.this.username, SendMail.this.password);
			}
		});
		session.setDebug(this.debug); // 显示调试信息
		return session;
	}
	// 发送文本邮件使用的方法
	static Message createTextMessage(Session session, String from, String to, String subject, String body)
			throws MessagingException {
     
		MimeMessage message = new MimeMessage(session);
		message.setFrom(new InternetAddress(from));
		message.setRecipient(Message.RecipientType.TO, new InternetAddress(to));
		message.setSubject(subject, "UTF-8");
		message.setText(body, "UTF-8");	// 发送文本邮件
		return message;
	}
	// 发送HTML格式文本邮件使用的方法
	static Message createHtmlMessage(Session session, String from, String to, String subject, String body)
			throws MessagingException {
     
		MimeMessage message = new MimeMessage(session);
		message.setFrom(new InternetAddress(from));
		message.setRecipient(Message.RecipientType.TO, new InternetAddress(to));
		message.setSubject(subject, "UTF-8");
		message.setText(body, "UTF-8", "html");
		return message;
	}
	// 发送带附件邮件使用的方法
	static Message createMessageWithAttachment(Session session, String from, String to, String subject, String body,
			String fileName, InputStream input) throws MessagingException, IOException {
     
		MimeMessage message = new MimeMessage(session);
		message.setFrom(new InternetAddress(from));
		message.setRecipient(Message.RecipientType.TO, new InternetAddress(to));
		message.setSubject(subject, "UTF-8");
		Multipart multipart = new MimeMultipart();		// 带附件
		// 添加text:
		BodyPart textpart = new MimeBodyPart();
		textpart.setContent(body, "text/html;charset=utf-8");
		multipart.addBodyPart(textpart);
		// 添加image:
		BodyPart imagepart = new MimeBodyPart();
		imagepart.setFileName(fileName);
		imagepart.setDataHandler(new DataHandler(new ByteArrayDataSource(input, "application/octet-stream")));
		multipart.addBodyPart(imagepart);
		message.setContent(multipart);
		return message;
	}
	// 将附件内嵌在文本中使用的方法
	static Message createMessageWithInlineImage(Session session, String from, String to, String subject, String body,
			String fileName, InputStream input) throws MessagingException, IOException {
     
		MimeMessage message = new MimeMessage(session);
		message.setFrom(new InternetAddress(from));
		message.setRecipient(Message.RecipientType.TO, new InternetAddress(to));
		message.setSubject(subject, "UTF-8");
		Multipart multipart = new MimeMultipart();
		// 添加text:
		BodyPart textpart = new MimeBodyPart();
		textpart.setContent(body, "text/html;charset=utf-8");
		multipart.addBodyPart(textpart);
		// 添加image:
		BodyPart imagepart = new MimeBodyPart();
		imagepart.setFileName(fileName);
		imagepart.setDataHandler(new DataHandler(new ByteArrayDataSource(input, "image/jpeg")));
		// 与HTML的关联:
		imagepart.setHeader("Content-ID", "");
		multipart.addBodyPart(imagepart);
		message.setContent(multipart);
		return message;
	}
}

接收邮件

• 常见的协议有POP3/IMAP协议，这里介绍POP3
  

// 可以打印出邮件信息
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import javax.mail.Address;
import javax.mail.Authenticator;
import javax.mail.BodyPart;
import javax.mail.Flags;
import javax.mail.Folder;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.Part;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Store;
import javax.mail.URLName;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMessage.RecipientType;
import javax.mail.internet.MimeUtility;
import com.sun.mail.pop3.POP3SSLStore;

public class Pop3 {
     
	final String popHost;
	final String username;
	final String password;
	final boolean debug;

	public Pop3(String popHost, String username, String password) {
     
		this.popHost = popHost;
		this.username = username;
		this.password = password;
		this.debug = true;
	}

	public static void main(String[] args) throws Exception {
     
		Pop3 pop = new Pop3("pop.qq.com", "[email protected]", "yr143364");
		Folder folder = null;
		Store store = null;
		try {
     
			store = pop.createSSLStore();
			folder = store.getFolder("INBOX");
			folder.open(Folder.READ_WRITE);
			System.out.println("Total messages: " + folder.getMessageCount());
			System.out.println("New messages: " + folder.getNewMessageCount());
			System.out.println("Unread messages: " + folder.getUnreadMessageCount());
			System.out.println("Deleted messages: " + folder.getDeletedMessageCount());
			Message[] messages = folder.getMessages();
			for (Message message : messages) {
     
				printMessage((MimeMessage) message);
			}
		} finally {
     
			if (folder != null) {
     
				try {
     
					folder.close(true);
				} catch (MessagingException e) {
     
					e.printStackTrace();
				}
			}
			if (store != null) {
     
				try {
     
					store.close();
				} catch (MessagingException e) {
     
					e.printStackTrace();
				}
			}
		}
	}

	public Store createSSLStore() throws MessagingException {
     
		Properties props = new Properties();
		props.setProperty("mail.store.protocol", "pop3");
		props.setProperty("mail.pop3.port", "995"); // 主机端口号
		props.setProperty("mail.pop3.host", this.popHost);// POP3主机名
		// 启动SSL:
		props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
		props.put("mail.smtp.socketFactory.port", "995");
		URLName url = new URLName("pop3", this.popHost, 995, "", this.username, this.password);
		Session session = Session.getInstance(props, null);
		session.setDebug(this.debug); // 显示调试信息
		Store store = new POP3SSLStore(session, url);
		store.connect();
		return store;
	}

	Session createTLSStore() {
     
		Properties props = new Properties();
		props.put("mail.smtp.host", this.popHost); // POP3主机名
		props.put("mail.smtp.port", "587"); // 主机端口号
		props.put("mail.smtp.auth", "true"); // 是否需要用户认证
		props.put("mail.smtp.starttls.enable", "true"); // 启用TLS加密
		Session session = Session.getInstance(props, new Authenticator() {
     
			protected PasswordAuthentication getPasswordAuthentication() {
     
				return new PasswordAuthentication(Pop3.this.username, Pop3.this.password);
			}
		});
		session.setDebug(this.debug); // 显示调试信息
		return session;
	}

	Session createInsecureStore() {
     
		Properties props = new Properties();
		props.put("mail.smtp.host", this.popHost); // POP3主机名
		props.put("mail.smtp.port", "25"); // 主机端口号
		props.put("mail.smtp.auth", "true"); // 是否需要用户认证
		Session session = Session.getInstance(props, new Authenticator() {
     
			protected PasswordAuthentication getPasswordAuthentication() {
     
				return new PasswordAuthentication(Pop3.this.username, Pop3.this.password);
			}
		});
		session.setDebug(this.debug); // 显示调试信息
		return session;
	}

	static void printMessage(MimeMessage msg) throws IOException, MessagingException {
     
		System.out.println("--------------------");
		System.out.println("Subject: " + MimeUtility.decodeText(msg.getSubject()));
		System.out.println("From: " + getFrom(msg));
		System.out.println("To: " + getTo(msg));
		System.out.println("Sent: " + msg.getSentDate().toString());
		System.out.println("Seen: " + msg.getFlags().contains(Flags.Flag.SEEN));
		System.out.println("Priority: " + getPriority(msg));
		System.out.println("Size: " + msg.getSize() / 1024 + "kb");
		System.out.println("Body: " + getBody(msg));
		System.out.println("--------------------");
		System.out.println();
	}

	static String getFrom(MimeMessage msg) throws IOException, MessagingException {
     
		Address[] froms = msg.getFrom();
		return addressToString(froms[0]);
	}

	static String getTo(MimeMessage msg) throws MessagingException, IOException {
     
		// 使用 msg.getAllRecipients() 获取所有收件人
		Address[] tos = msg.getRecipients(RecipientType.TO);
		List<String> list = new ArrayList<>();
		for (Address to : tos) {
     
			list.add(addressToString(to));
		}
		return String.join(", ", list);
	}

	static String addressToString(Address addr) throws IOException {
     
		InternetAddress address = (InternetAddress) addr;
		String personal = address.getPersonal();
		return personal == null ? address.getAddress()
				: (MimeUtility.decodeText(personal) + " <" + address.getAddress() + ">");
	}

	static String getPriority(MimeMessage msg) throws MessagingException {
     
		String priority = "Normal";
		String[] headers = msg.getHeader("X-Priority");
		if (headers != null) {
     
			String header = headers[0];
			if ("1".equals(header) || "high".equalsIgnoreCase(header)) {
     
				priority = "High";
			} else if ("5".equals(header) || "low".equalsIgnoreCase(header)) {
     
				priority = "Low";
			}
		}
		return priority;
	}

	static String getBody(Part part) throws MessagingException, IOException {
     
		if (part.isMimeType("text/*")) {
     
			return part.getContent().toString();
		}
		if (part.isMimeType("multipart/*")) {
     
			Multipart multipart = (Multipart) part.getContent();
			for (int i = 0; i < multipart.getCount(); i++) {
     
				BodyPart bodyPart = multipart.getBodyPart(i);
				String body = getBody(bodyPart);
				if (!body.isEmpty()) {
     
					return body;
				}
			}
		}
		return "";
	}
}

HTTP请求响应协议

• 基于TCP的高级网络传输协议
  
• POST请求既有header又有body
  
  
• HTTP响应格式：
  
• 这里介绍HTTP客户端请求：
• Java提供了HttpURLConnection实现客户端

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

class Response {
     
	final int code;
	final byte[] data;

	public Response(int code, byte[] data) {
     
		this.code = code;
		this.data = data;
	}

	@Override
	public String toString() {
     
		StringBuilder sb = new StringBuilder(1024);
		sb.append(code).append("\n");
		String s = new String(data, StandardCharsets.UTF_8);
		if (s.length() > 1024) {
     
			sb.append(s.substring(0, 1024)).append("\n...");
		} else {
     
			sb.append(s);
		}
		return sb.toString();
	}
}

public class HttpClient {
     
	public static void main(String[] args) throws Exception {
     
		Response resp = get("https://www.douban.com");
		System.out.println(resp);// get请求
		Map<String, String> postMap = new HashMap<>();// 模拟post表单
		postMap.put("form_email", "test");
		postMap.put("form_password", "password");
		Response postResp = post("https://www.douban.com/accounts/login", "application/x-www-form-urlencoded",
				toFormData(postMap));// post请求
		System.out.println(postResp);
	}

	static Response get(String theUrl) {
     
		System.err.println("GET: " + theUrl);
		HttpURLConnection conn = null;
		try {
     
			URL url = new URL(theUrl);
			conn = (HttpURLConnection) url.openConnection();
			ByteArrayOutputStream responseBuffer = new ByteArrayOutputStream();
			try (InputStream input = conn.getInputStream()) {
     
				byte[] buffer = new byte[1024];
				for (;;) {
     
					int n = input.read(buffer);
					if (n == (-1)) {
     
						break;
					}
					responseBuffer.write(buffer, 0, n);
				}
			}
			return new Response(conn.getResponseCode(), responseBuffer.toByteArray());
		} catch (IOException e) {
     
			throw new RuntimeException(e);
		} finally {
     
			if (conn != null) {
     
				conn.disconnect();
			}
		}
	}

	static Response post(String theUrl, String contentType, String contentData) {
     
		System.err.println("POST: " + theUrl);
		HttpURLConnection conn = null;
		try {
     
			URL url = new URL(theUrl);
			conn = (HttpURLConnection) url.openConnection();
			conn.setRequestMethod("POST");
			conn.setDoOutput(true);	// 表示需要发送数据
			byte[] postData = contentData.getBytes(StandardCharsets.UTF_8);
			conn.setRequestProperty("Content-Type", contentType);
			conn.setRequestProperty("Content-Length", String.valueOf(postData.length));
			try (OutputStream output = conn.getOutputStream()) {
     
				output.write(postData);
			}
			ByteArrayOutputStream responseBuffer = new ByteArrayOutputStream();
			try (InputStream input = conn.getInputStream()) {
     
				byte[] buffer = new byte[1024];
				for (;;) {
     
					int n = input.read(buffer);
					if (n == (-1)) {
     
						break;
					}
					responseBuffer.write(buffer, 0, n);
				}
			}
			return new Response(conn.getResponseCode(), responseBuffer.toByteArray());
		} catch (IOException e) {
     
			throw new RuntimeException(e);
		} finally {
     
			if (conn != null) {
     
				conn.disconnect();
			}
		}
	}

	static String toFormData(Map<String, String> map) throws IOException {
     
		List<String> list = new ArrayList<>(map.size());
		for (String key : map.keySet()) {
     
			list.add(key + "=" + URLEncoder.encode(map.get(key), "UTF-8"));
		}
		return String.join("&", list);
	}
}

RMI远程调用

• Remote Method Invocation：将一个接口暴露给远程
• 底层原理：
  

1. 定义一个interface

import java.rmi.Remote;
import java.rmi.RemoteException;
import java.time.LocalDateTime;

public interface Clock extends Remote {
     	// 必须继承自Remote
	LocalDateTime currentTime() throws RemoteException;	// 必须抛出
}

2. 实现类

import java.rmi.RemoteException;
import java.time.LocalDateTime;

public class ClockImpl implements Clock {
     	// 继承接口
	@Override
	public LocalDateTime currentTime() throws RemoteException {
     
		return LocalDateTime.now();
	}
}

3. server

import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
import java.rmi.server.UnicastRemoteObject;

public class ClockServer {
     
	public static void main(String[] args) throws Exception {
     
		Clock impl = new ClockImpl();
		// 得到一个stub对象
		Clock stub = (Clock) UnicastRemoteObject.exportObject(impl, 1099);// 1099端口
		LocateRegistry.createRegistry(1099);
		Registry registry = LocateRegistry.getRegistry();
		registry.bind("Clock", stub);	// 绑定stub对象而非实例，远程调用需要使用这个名称
		System.out.println("Clock server ready.");
	}
}

4. client

import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
import java.time.LocalDateTime;

public class ClockClient {
     
	public static void main(String[] args) throws Exception {
     
		Registry registry = LocateRegistry.getRegistry(null); // null = "localhost"，建立远程连接
		Clock clock = (Clock) registry.lookup("Clock");	// 获得远程对象的引用
		LocalDateTime dt = clock.currentTime();	// 调用RMI方法
		System.out.println("RMI result: " + dt);
	}
}

• 服务器端通过自动生成的stub类接收远程调用请求

XML&JSON

XML

• eXtensible Markup Language，是一种数据格式
• 可以描述非常复杂的数据结构，用于传输和存储数据
• 特点：纯文本（默认utf8编码），可嵌套（结构化）
  

.dtd 表示数据结构可以被DTD或XSD验证
isbn 元素必须包含属性lang

• 了解即可：
  
• 特殊字符表示

字符	表示
<	<
>	>
&	&
"	"
’	'

解析XML

• 两种标准的解析XML的API：

1. DOM：一次性读取XML，在内存中表示为树形结构
2. SAX：以流的形式读取，使用事件回调

• DOM（文档对象模型 ）
  

注：W3C DOM 标准被分为 3 个不同的部分：

• 核心 DOM - 针对任何结构化文档的标准模型
• XML DOM - 针对 XML 文档的标准模型
• HTML DOM - 针对 HTML 文档的标准模型

• 核心API

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();// 操作工场
DocumentBuilder db = dbf.newDocumentBuilder();// 操作类
Document doc = db.parse('./hello.xml');// 传入文档
Element elt = doc.getDocumentElement();

• Java Dom Node
  
• 所有的节点包括Document都可以看做Node

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Node;

public class DOMSample {
     
	static final String XML_URL = "http://rss.sina.com.cn/tech/internet/home28.xml";

	public static void main(String[] args) throws Exception {
     
		DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
		DocumentBuilder db = dbf.newDocumentBuilder();
		Document doc = db.parse(XML_URL);
		printNode(doc, 0);
	}
	static void printNode(Node n, int indent) {
     
		for (int i = 0; i < indent; i++) {
     
			System.out.print(' ');
		}
		switch (n.getNodeType()) {
     
		case Node.DOCUMENT_NODE:	// 文档节点也视为Node
			System.out.println("Document: " + n.getNodeName());
			break;
		case Node.ELEMENT_NODE:
			System.out.println("Element: " + n.getNodeName());
			break;
		case Node.TEXT_NODE:
			System.out.println("Text: " + n.getNodeName() + " = " + n.getNodeValue());
			break;
		case Node.ATTRIBUTE_NODE:
			System.out.println("Attr: " + n.getNodeName() + " = " + n.getNodeValue());
			break;
		case Node.CDATA_SECTION_NODE:
			System.out.println("CDATA: " + n.getNodeName() + " = " + n.getNodeValue());
			break;
		case Node.COMMENT_NODE:
			System.out.println("Comment: " + n.getNodeName() + " = " + n.getNodeValue());
			break;
		default:
			System.out.println("NodeType: " + n.getNodeType() + ", NodeName: " + n.getNodeName());
		}
		for (Node child = n.getFirstChild(); child != null; child = child.getNextSibling()) {
     
			printNode(child, indent + 1);
		}
	}
}

JSON

• json是一种类似JavaScript对象的数据表示格式（JavaScript Object Notation）
• 去除了JavaScript的执行语句，仅保留数据
• 特点：只允许使用utf-8编码，必须使用双引号，特殊字符使用\转义
• 适合表示层次结构，结构简单速度快
• 浏览器直接支持json的读写，因此非常适合REST API做数据通讯

REST API是前后端分离的一套标准

// json数据，key-value形式
{
     
    "data": [{
     
            "name": "RoyKun"
        },
        {
     
            "age": 22
        },
        {
     
            "hobby": [{
     
                "first": "study"
            }, {
     
                "second": "play"
            }, {
     
                "third": "sport"
            }]
        },
        {
     
            "language": ["C", "java", "Python"]
        },
        "just a test"
    ]
}

解析JSON

• JSR 353 API
• 第三方库（Jackson、Gson等）
• 使用Jackson：

// 使用Jackson
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;

public class JsonToBean {
     
	// 豆瓣API搜索
	static final String JSON_URL = "https://api.douban.com/v2/book/search?q=";

	public static void main(String[] args) throws Exception {
     
		ObjectMapper mapper = new ObjectMapper().registerModule(new JavaTimeModule());// 日期时间格式
		mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);// 忽略在javabean中找不到的属性
		String json = search("java");// 返回下载的json字符串
		SearchResult result = mapper.readValue(json, SearchResult.class);// 可以直接把一个json字符串反序列化为指定的javabean对象，这里指定为SearchResult了
		// SearchResult的定义会事先参考下载的json数据
		// 再将javabean对象转化为json输出
		System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(result));
		// 这样倒腾一下可以理解成规范数据
	}

	static String search(String q) {
     
		HttpURLConnection conn = null;
		StringBuilder sb = new StringBuilder(4096);
		try {
     
			URL url = new URL(JSON_URL + URLEncoder.encode(q, "UTF-8"));
			conn = (HttpURLConnection) url.openConnection();
			if (200 == conn.getResponseCode()) {
     
				try (BufferedReader reader = new BufferedReader(
						new InputStreamReader(conn.getInputStream(), "UTF-8"))) {
     
					char[] buffer = new char[1024];
					for (;;) {
     
						int n = reader.read(buffer);
						if (n == (-1)) {
     
							break;
						}
						sb.append(buffer, 0, n);
					}
				}
				return sb.toString();
			}
			throw new RuntimeException("Bad response code: " + conn.getResponseCode());
		} catch (IOException e) {
     
			throw new RuntimeException(e);
		} finally {
     
			if (conn != null) {
     
				conn.disconnect();
			}
		}
	}
}

// javabean
import java.util.List;

public class SearchResult {
     	// 数据成员
	public long count;
	public long total;
	public List<Book> books;
}

import java.time.LocalDate;
import java.util.List;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;

public class Book {
     
	public String id;
	public String title;
	public String subtitle;
	public List<String> author;

	// 使用Annotion定制序列化和反序列化
	@JsonSerialize(using = CustomLocalDateSerializer.class)
	@JsonDeserialize(using = CustomLocalDateDeserializer.class)
	public LocalDate pubdate;// 会用到上面的序列化和反序列化，都是自定义的对数据成员的小操作
	public String url;
	public String price;
}

在解释一下什么是JavaBean：
JavaBean 是一种JAVA语言写成的可重用组件。为写成JavaBean，类必须是具体的和公共的，并且具有无参数的构造器。JavaBean 通过提供符合一致性设计模式的公共方法暴露成员属性，即set和get方法。众所周知，属性名称符合这种模式，其他Java 类可以通过反射机制发现和操作这些JavaBean 的属性

// 自定义注解，格式化数据
import java.io.IOException;
import java.time.LocalDate;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;

public class CustomLocalDateSerializer extends JsonSerializer<LocalDate> {
     // 数据序列化
	@Override
	public void serialize(LocalDate value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
     
		gen.writeString(value.toString());	// 使用自定义的方法封装对象
	}
}

import java.io.IOException;
import java.time.DateTimeException;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Locale;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;

public class CustomLocalDateDeserializer extends JsonDeserializer<LocalDate> {
     // 反序列化数据

	static DateTimeFormatter FORMATTER = DateTimeFormatter.ofPattern("yyyy-M-d", Locale.US);

	@Override
	public LocalDate deserialize(JsonParser p, DeserializationContext ctxt)
			throws IOException, JsonProcessingException {
     
		String s = p.getValueAsString();
		if (s != null) {
     
			try {
     
				return LocalDate.parse(s, FORMATTER);	// 使用自定义的格式解析对象
			} catch (DateTimeException e) {
     
				// ignore
			}
		}
		return null;
	}
}

• Jackson提供了读写json的API，实现了json和javabean的相互转换，可使用Annotion定制序列化和反序列化