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1、对输入输出流、字符字节流的学习，以之前做的批量下载功能为例

批量下载指的是，将多个文件打包到zip文件中，然后下载该zip文件。

1.1下载网络上的文件

代码参考如下：

import java.io.*;
import java.net.URL;
import java.net.URLConnection;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;public class MultiDownloadByUrlTest {public static void main(String[] args) throws IOException {//如果zip文件不存在则创建zipString localZipFile = "D:/temp/testUrl.zip" ;File file = new File(localZipFile);if(!file.exists()){file.createNewFile();}ZipOutputStream out = new ZipOutputStream(new FileOutputStream(localZipFile));byte[] buffer = new byte[1024];//要批量下载的文件数组String[] urls = new String[] {"http://www.baidu.com/img/PCfb_5bf082d29588c07f842ccde3f97243ea.png","https://img-home.csdnimg.cn/images/20201124032511.png"};//依次获取批量下载的文件for(int i =0; i<urls.length;i++){//从数据库中获取文件的路径和文件名,并放入zip文件中String urlFile = urls[i];out.putNextEntry(new ZipEntry(i+".png"));int len;URL url = new URL(urlFile);URLConnection conn = url.openConnection();InputStream inStream = conn.getInputStream();//读入需要下载的文件的内容，打包到zip文件while ((len = inStream.read(buffer)) > 0) {out.write(buffer, 0, len);}out.closeEntry();inStream.close();}out.close();}}

1.2、下载磁盘中的多个文件到zip文件中

import java.io.*;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;public class MultiDownloadTest {public static void main(String[] args) throws IOException {//如果zip文件不存在则创建zipString localZipFile = "D:/temp/test.zip" ;File file = new File(localZipFile);if(!file.exists()){file.createNewFile();}ZipOutputStream out = new ZipOutputStream(new FileOutputStream(localZipFile));//要批量下载的文件数组String[] ids = new String[] {"11.docx","22.xlsx"};byte[] buffer = new byte[1024];//依次获取批量下载的文件for(int i =0; i<ids.length;i++){String fileName = ids[i];out.putNextEntry(new ZipEntry(fileName));int len;FileInputStream inStream = new FileInputStream(new File("D:/temp/"+fileName));//读入需要下载的文件的内容，打包到zip文件while ((len = inStream.read(buffer)) > 0) {out.write(buffer, 0, len);}out.closeEntry();inStream.close();}out.close();}}

1.3编写接口，下载该zip文件

Controller类代码如下：

package com.hmblogs.backend.controller;import com.hmblogs.backend.util.MultiDownloadTest;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.bind.annotation.*;import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;@RestController
@Slf4j
public class FileController {/*** get方式下载zip文件* @return*/@GetMapping(value = "/downloadZipByGet")public void downloadZipByGet(HttpServletRequest request,HttpServletResponse response) throws IOException {log.info("downloadZipByGet prepare begin.");MultiDownloadTest.preMultiDownload();log.info("downloadZipByGet prepare end.");log.info("downloadZipByGet begin.");String zipFileName = "D:/temp/test.zip";InputStream is = new FileInputStream(new File(zipFileName));// 设置response参数，可以打开下载页面response.reset();response.setContentType("application/octet-stream;charset=utf-8");response.setHeader("Access-Control-Expose-Headers", "content-disposition");response.setHeader("Content-Disposition", "attachment;filename=test.zip");ServletOutputStream out = response.getOutputStream();BufferedInputStream bis = null;BufferedOutputStream bos = null;try {bis = new BufferedInputStream(is);bos = new BufferedOutputStream(out);byte[] buff = new byte[2048];int bytesRead;while (-1 != (bytesRead = bis.read(buff, 0, buff.length))) {bos.write(buff, 0, bytesRead);}log.info("downloadZipByGet end.");} catch (final IOException e) {log.error("downloadZipByGet errors, reason:{}", e.getMessage());} finally {if (bis != null){bis.close();}if (is != null){is.close();}if (bos != null){bos.close();}if (out != null){out.close();}}// 用后删除临时用途的zip文件File fileTempZip = new File(zipFileName);if(fileTempZip.exists()){fileTempZip.delete();}}/*** post方式下载zip文件* @return*/@RequestMapping(value = "/downloadZipByPost",method = RequestMethod.POST)public void downloadZipByPost(){}}

工具类MultiDownloadTest.java代码如下：

package com.hmblogs.backend.util;import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;public class MultiDownloadTest {public static void preMultiDownload() throws IOException {//如果zip文件不存在则创建zipString localZipFile = "D:/temp/test.zip" ;File file = new File(localZipFile);if(!file.exists()){file.createNewFile();}ZipOutputStream out = new ZipOutputStream(new FileOutputStream(localZipFile));//要批量下载的文件数组String[] ids = new String[] {"11.docx","22.xlsx"};byte[] buffer = new byte[1024];//依次获取批量下载的文件for(int i =0; i<ids.length;i++){String fileName = ids[i];out.putNextEntry(new ZipEntry(fileName));int len;FileInputStream inStream = new FileInputStream(new File("D:/temp/"+fileName));//读入需要下载的文件的内容，打包到zip文件while ((len = inStream.read(buffer)) > 0) {out.write(buffer, 0, len);}out.closeEntry();inStream.close();}out.close();}}

1.4访问接口

http://localhost:8080/backend/downloadZipByGet

下载了文件，能正常打开，且文件都是正常的。

二、学习NIO

参考Java之NIO基本简介_java_脚本之家

2.1开发一个简单的服务端接收客户端发过来的消息的功能

服务端Server.java代码如下：

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Iterator;
public class Server {public static void main(String[] args) {try {//1.获取管道ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();//2.设置非阻塞模式serverSocketChannel.configureBlocking(false);//3.绑定端口serverSocketChannel.bind(new InetSocketAddress(8888));//4.获取选择器Selector selector = Selector.open();//5.将通道注册到选择器上，并且开始指定监听的接收事件serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);//6.轮询已经就绪的事件while (selector.select() > 0){System.out.println("开启事件处理");//7.获取选择器中所有注册的通道中已准备好的事件Iterator<SelectionKey> it = selector.selectedKeys().iterator();//8.开始遍历事件while (it.hasNext()){SelectionKey selectionKey = it.next();//9.判断这个事件具体是啥if (selectionKey.isAcceptable()){System.out.println("isAcceptable--->"+selectionKey);//10.获取当前接入事件的客户端通道SocketChannel socketChannel = serverSocketChannel.accept();//11.切换成非阻塞模式socketChannel.configureBlocking(false);//12.将本客户端注册到选择器socketChannel.register(selector,SelectionKey.OP_READ);}else if (selectionKey.isReadable()){System.out.println("isReadable--->"+selectionKey);//13.获取当前选择器上的读SocketChannel socketChannel = (SocketChannel) selectionKey.channel();//14.读取ByteBuffer buffer = ByteBuffer.allocate(1024);int len;while ((len = socketChannel.read(buffer)) > 0){buffer.flip();System.out.println(new String(buffer.array(),0,len));//清除之前的数据（覆盖写入）buffer.clear();}}//15.处理完毕后，移除当前事件it.remove();}}} catch (IOException e) {e.printStackTrace();}}
}

客户端Client.java代码如下：

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SocketChannel;
import java.util.Scanner;
public class Client {public static void main(String[] args) {try {SocketChannel socketChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1",8888));socketChannel.configureBlocking(false);ByteBuffer buffer = ByteBuffer.allocate(1024);Scanner scanner = new Scanner(System.in);while (true){System.out.print("请输入:");String msg = scanner.nextLine();buffer.put(msg.getBytes());buffer.flip();socketChannel.write(buffer);buffer.clear();}} catch (IOException e) {e.printStackTrace();}}
}

运行Server

然后运行Client

在Client输入wwww

然后看到Server打印如下内容：

开启事件处理
isAcceptable--->sun.nio.ch.SelectionKeyImpl@42110406
开启事件处理
isReadable--->sun.nio.ch.SelectionKeyImpl@531d72ca
wwww

可以看到， 这时先开启了isAcceptable事件处理，然后开启了isReadable事件处理。

然后再在Client输入qqqq

然后看到Server打印如下内容：

开启事件处理
isReadable--->sun.nio.ch.SelectionKeyImpl@531d72ca
qqqq

这时只开启了isReadable这样的事件处理，不用再开启isAcceptable事件处理

server控制台截图如下

client的控制台如下： 

2.2开发网络编程应用实例-群聊系统

需求：进一步理解 NIO 非阻塞网络编程机制，实现多人群聊

 编写一个 NIO 群聊系统，实现客户端与客户端的通信需求（非阻塞）

服务器端：可以监测用户上线，离线，并实现消息转发功能

客户端：通过 channel 可以无阻塞发送消息给其它所有客户端用户，同时可以接受其它客户端用户通过服务端转发来的消息

Server.java代码如下：

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Iterator;
/****/
public class Server {//定义属性private Selector selector;private ServerSocketChannel ssChannel;private static final int PORT = 9999;//构造器//初始化工作public Server() {try {// 1、获取通道ssChannel = ServerSocketChannel.open();// 2、切换为非阻塞模式ssChannel.configureBlocking(false);// 3、绑定连接的端口ssChannel.bind(new InetSocketAddress(PORT));// 4、获取选择器Selectorselector = Selector.open();// 5、将通道都注册到选择器上去，并且开始指定监听接收事件ssChannel.register(selector , SelectionKey.OP_ACCEPT);}catch (IOException e) {e.printStackTrace();}}//监听public void listen() {System.out.println("监听线程:" + Thread.currentThread().getName());try {while (selector.select() > 0){// 7、获取选择器中的所有注册的通道中已经就绪好的事件Iterator<SelectionKey> it = selector.selectedKeys().iterator();// 8、开始遍历这些准备好的事件while (it.hasNext()){// 提取当前这个事件SelectionKey sk = it.next();// 9、判断这个事件具体是什么if(sk.isAcceptable()){// 10、直接获取当前接入的客户端通道SocketChannel schannel = ssChannel.accept();// 11 、切换成非阻塞模式schannel.configureBlocking(false);// 12、将本客户端通道注册到选择器System.out.println(schannel.getRemoteAddress() + " 上线 ");schannel.register(selector , SelectionKey.OP_READ);//提示}else if(sk.isReadable()){//处理读 (专门写方法..)readData(sk);}it.remove(); // 处理完毕之后需要移除当前事件}}}catch (Exception e) {e.printStackTrace();}finally {//发生异常处理....}}//读取客户端消息private void readData(SelectionKey key) {//获取关联的channelSocketChannel channel = null;try {//得到channelchannel = (SocketChannel) key.channel();//创建bufferByteBuffer buffer = ByteBuffer.allocate(1024);int count = channel.read(buffer);//根据count的值做处理if(count > 0) {//把缓存区的数据转成字符串String msg = new String(buffer.array());//输出该消息System.out.println("来自客户端---> " + msg);//向其它的客户端转发消息(去掉自己), 专门写一个方法来处理sendInfoToOtherClients(msg, channel);}}catch (IOException e) {try {System.out.println(channel.getRemoteAddress() + " 离线了..");e.printStackTrace();//取消注册key.cancel();//关闭通道channel.close();}catch (IOException e2) {e2.printStackTrace();;}}}//转发消息给其它客户(通道)private void sendInfoToOtherClients(String msg, SocketChannel self ) throws  IOException{System.out.println("服务器转发消息中...");System.out.println("服务器转发数据给客户端线程: " + Thread.currentThread().getName());//遍历 所有注册到selector 上的 SocketChannel,并排除 selffor(SelectionKey key: selector.keys()) {//通过 key  取出对应的 SocketChannelChannel targetChannel = key.channel();//排除自己if(targetChannel instanceof  SocketChannel && targetChannel != self) {//转型SocketChannel dest = (SocketChannel)targetChannel;//将msg 存储到bufferByteBuffer buffer = ByteBuffer.wrap(msg.getBytes());//将buffer 的数据写入 通道dest.write(buffer);}}}public static void main(String[] args) {//创建服务器对象Server groupChatServer = new Server();groupChatServer.listen();}
}

Client.java代码如下：

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Scanner;
public class Client {//定义相关的属性private final String HOST = "127.0.0.1"; // 服务器的ipprivate final int PORT = 9999; //服务器端口private Selector selector;private SocketChannel socketChannel;private String username;//构造器, 完成初始化工作public Client() throws IOException {selector = Selector.open();//连接服务器socketChannel = socketChannel.open(new InetSocketAddress("127.0.0.1", PORT));//设置非阻塞socketChannel.configureBlocking(false);//将channel 注册到selectorsocketChannel.register(selector, SelectionKey.OP_READ);//得到usernameusername = socketChannel.getLocalAddress().toString().substring(1);System.out.println(username + " is ok...");}//向服务器发送消息public void sendInfo(String info) {info = username + " 说：" + info;try {socketChannel.write(ByteBuffer.wrap(info.getBytes()));}catch (IOException e) {e.printStackTrace();}}//读取从服务器端回复的消息public void readInfo() {try {int readChannels = selector.select();if(readChannels > 0) {//有可以用的通道Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();while (iterator.hasNext()) {SelectionKey key = iterator.next();if(key.isReadable()) {//得到相关的通道SocketChannel sc = (SocketChannel) key.channel();//得到一个BufferByteBuffer buffer = ByteBuffer.allocate(1024);//读取sc.read(buffer);//把读到的缓冲区的数据转成字符串String msg = new String(buffer.array());System.out.println(msg.trim());}}iterator.remove(); //删除当前的selectionKey, 防止重复操作} else {//System.out.println("没有可以用的通道...");}}catch (Exception e) {e.printStackTrace();}}public static void main(String[] args) throws Exception {//启动我们客户端Client chatClient = new Client();//启动一个线程, 每个3秒，读取从服务器发送数据new Thread() {public void run() {while (true) {chatClient.readInfo();try {Thread.currentThread().sleep(3000);}catch (InterruptedException e) {e.printStackTrace();}}}}.start();//发送数据给服务器端Scanner scanner = new Scanner(System.in);while (scanner.hasNextLine()) {System.out.print("请输入:");String s = scanner.nextLine();chatClient.sendInfo(s);}}
}

Client22.java代码如下：就是Client.java的代码复制一份，改下文件名而已。

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Scanner;public class Client22 {//定义相关的属性private final String HOST = "127.0.0.1"; // 服务器的ipprivate final int PORT = 9999; //服务器端口private Selector selector;private SocketChannel socketChannel;private String username;//构造器, 完成初始化工作public Client22() throws IOException {selector = Selector.open();//连接服务器socketChannel = socketChannel.open(new InetSocketAddress("127.0.0.1", PORT));//设置非阻塞socketChannel.configureBlocking(false);//将channel 注册到selectorsocketChannel.register(selector, SelectionKey.OP_READ);//得到usernameusername = socketChannel.getLocalAddress().toString().substring(1);System.out.println(username + " is ok...");}//向服务器发送消息public void sendInfo(String info) {info = username + " 说：" + info;try {socketChannel.write(ByteBuffer.wrap(info.getBytes()));}catch (IOException e) {e.printStackTrace();}}//读取从服务器端回复的消息public void readInfo() {try {int readChannels = selector.select();if(readChannels > 0) {//有可以用的通道Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();while (iterator.hasNext()) {SelectionKey key = iterator.next();if(key.isReadable()) {//得到相关的通道SocketChannel sc = (SocketChannel) key.channel();//得到一个BufferByteBuffer buffer = ByteBuffer.allocate(1024);//读取sc.read(buffer);//把读到的缓冲区的数据转成字符串String msg = new String(buffer.array());System.out.println(msg.trim());}}iterator.remove(); //删除当前的selectionKey, 防止重复操作} else {//System.out.println("没有可以用的通道...");}}catch (Exception e) {e.printStackTrace();}}public static void main(String[] args) throws Exception {//启动我们客户端Client22 chatClient = new Client22();//启动一个线程, 每个3秒，读取从服务器发送数据new Thread() {public void run() {while (true) {chatClient.readInfo();try {Thread.currentThread().sleep(3000);}catch (InterruptedException e) {e.printStackTrace();}}}}.start();//发送数据给服务器端Scanner scanner = new Scanner(System.in);while (scanner.hasNextLine()) {System.out.print("请输入:");String s = scanner.nextLine();chatClient.sendInfo(s);}}
}

启动Server、Client、Client22后，在Client输入内容、在Client22输入内容后，对3个控制台截图如下

Server控制台截图如下：

Client控制台如下：

Client22控制台如下：

 

简单的需求目的达到了。