网络编程与通信原理

柔情只为你懂 2023-10-03 22:04 118阅读 0赞

## 一、基础概念 ##

不同设备之间通过网络进行数据传输，并且基于通用的网络协议作为多种设备的兼容标准，称为网络通信；

![format_png][]

以C/S架构来看，在一次请求当中，客户端和服务端进行数据传输的交互时，在不同阶段和层次中需要遵守的网络通信协议也不一样；

应用层：HTTP超文本传输协议，基于TCP/IP通信协议来传递数据；

传输层：TCP传输控制协议，采用三次握手的方式建立连接，形成数据传输通道；

网络层：IP协议，作用是把各种传输的数据包发送给请求的接收方；

![format_png 1][]

通信双方进行交互时，发送方数据在各层传输时，每通过一层就会添加该层的首部信息；接收方与之相反，每通过一次就会删除该层的首部信息；

## 二、JDK源码 ##

在`java.net`源码包中，提供了与网络编程相关的基础API；

### 1、InetAddress ###

封装了对IP地址的相关操作，在使用该API之前可以先查看本机的`hosts`的映射，Linux系统中在`/etc/hosts`路径下；

import java.net.InetAddress;
    public class TestInet {
    
        public static void main(String[] args) throws Exception {
            // 获取本机 InetAddress 对象
            InetAddress localHost = InetAddress.getLocalHost();
            printInetAddress(localHost);
            // 获取指定域名 InetAddress 对象
            InetAddress inetAddress = InetAddress.getByName("www.baidu.com");
            printInetAddress(inetAddress);
            // 获取本机配置 InetAddress 对象
            InetAddress confAddress = InetAddress.getByName("nacos-service");
            printInetAddress(confAddress);
        }
    
        public static void printInetAddress (InetAddress inetAddress){
            System.out.println("InetAddress："+inetAddress);
            System.out.println("主机名："+inetAddress.getHostName());
            System.out.println("IP地址："+inetAddress.getHostAddress());
        }
    }
    复制代码

### 2、URL ###

统一资源定位符，URL一般包括：协议、主机名、端口、路径、查询参数、锚点等，路径+查询参数，也被称为文件；

![format_png 2][]

import java.net.URL;
    public class TestURL {
        public static void main(String[] args) throws Exception {
            URL url = new URL("https://www.baidu.com:80/s?wd=Java#bd") ;
            printURL(url);
        }
        private static void printURL (URL url){
            System.out.println("协议：" + url.getProtocol());
            System.out.println("域名：" + url.getHost());
            System.out.println("端口：" + url.getPort());
            System.out.println("路径：" + url.getPath());
            System.out.println("参数：" + url.getQuery());
            System.out.println("文件：" + url.getFile());
            System.out.println("锚点：" + url.getRef());
        }
    }
    复制代码

### 3、HttpURLConnection ###

作为URLConnection的抽象子类，用来处理针对Http协议的请求，可以设置连接超时、读取超时、以及请求的其他属性，是服务间通信的常用方式；

public class TestHttp {
        public static void main(String[] args) throws Exception {
            // 访问 网址 内容
            URL url = new URL("https://www.jd.com");
            HttpURLConnection httpUrlConnection = (HttpURLConnection) url.openConnection();
            printHttp(httpUrlConnection);
    
            // 请求 服务 接口
            URL api = new URL("http://localhost:8082/info/99");
            HttpURLConnection apiConnection = (HttpURLConnection) api.openConnection();
            apiConnection.setRequestMethod("GET");
            apiConnection.setConnectTimeout(3000);
            printHttp(apiConnection);
        }
    
        private static void printHttp (HttpURLConnection httpUrlConnection) throws Exception{
            try (InputStream inputStream = httpUrlConnection.getInputStream()) {
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
                String line ;
                while ((line = bufferedReader.readLine()) != null) {
                    System.out.println(line);
                }
            }
        }
    }
    复制代码

## 三、通信编程 ##

### 1、Socket ###

Socket也被称为套接字，是两台设备之间通信的端点，会把网络连接当成流处理，则数据以IO形式传输，这种方式在当前被普遍采用；

![format_png 3][]

从网络编程直接跳到Socket套接字，概念上确实有较大跨度，概念过度抽象时，可以看看源码的核心结构，在理解时会轻松很多，在JDK中重点看SocketImpl抽象类；

public abstract class SocketImpl implements SocketOptions {
        // Socket对象，客户端和服务端
        Socket socket = null;
        ServerSocket serverSocket = null;
        // 套接字的文件描述对象
        protected FileDescriptor fd;
        // 套接字的路由IP地址
        protected InetAddress address;
        // 套接字连接到的远程主机上的端口号
        protected int port;
        // 套接字连接到的本地端口号
        protected int localport;
    }
    复制代码

套接字的抽象实现类，是实现套接字的所有类的公共超类，可以用于创建客户端和服务器套接字；

所以到底如何理解Socket概念？从抽象类中来看，套接字就是指代网络通讯中系统资源的核心标识，比如通讯方IP地址、端口、状态等；

### 2、SocketServer ###

创建Socket服务端，并且在8989端口监听，接收客户端的连接请求和相关信息，并且响应客户端，发送指定的数据；

public class SocketServer {
        public static void main(String[] args) throws Exception {
            // 1、创建Socket服务端
            ServerSocket serverSocket = new ServerSocket(8989);
            System.out.println("socket-server:8989，waiting connect...");
            // 2、方法阻塞等待，直到有客户端连接
            Socket socket = serverSocket.accept();
            System.out.println("socket-server:8989，get connect:"+socket.getPort());
            // 3、输入流，输出流
            InputStream inStream = socket.getInputStream();
            OutputStream outStream = socket.getOutputStream();
            // 4、数据接收和响应
            byte[] buf = new byte[1024];
            int readLen = 0;
            while ((readLen=inStream.read(buf)) != -1){
                // 接收数据
                String readVar = new String(buf, 0, readLen) ;
                if ("exit".equals(readVar)){
                    break ;
                }
                System.out.println("recv："+readVar+"；time："+DateTime.now().toString(DatePattern.NORM_DATETIME_PATTERN));
                // 响应数据
                outStream.write(("resp-time："+DateTime.now().toString(DatePattern.NORM_DATETIME_PATTERN)).getBytes());
            }
            // 5、资源关闭
            outStream.close();
            inStream.close();
            socket.close();
            serverSocket.close();
            System.out.println("socket-server:8989，exit...");
        }
    }
    复制代码

需要注意的是步骤2输出的端口号是随机不确定的，结合`jps`和`lsof -i tcp:port`命令查看进程和端口号的占用情况；

### 3、SocketClient ###

创建Socket客户端，并且连接到服务端，读取命令行输入的内容并发送到服务端，并且输出服务端的响应数据；

public class SocketClient {
        public static void main(String[] args) throws Exception {
            // 1、创建Socket客户端
            Socket socket = new Socket(InetAddress.getLocalHost(), 8989);
            System.out.println("server-client，connect to:8989");
            // 2、输入流，输出流
            OutputStream outStream = socket.getOutputStream();
            InputStream inStream = socket.getInputStream();
            // 3、数据发送和响应接收
            int readLen = 0;
            byte[] buf = new byte[1024];
            while (true){
                // 读取命令行输入
                BufferedReader bufReader = new BufferedReader(new InputStreamReader(System.in));
                String iptLine = bufReader.readLine();
                if ("exit".equals(iptLine)){
                    break;
                }
                // 发送数据
                outStream.write(iptLine.getBytes());
                // 接收数据
                if ((readLen = inStream.read(buf)) != -1) {
                    System.out.println(new String(buf, 0, readLen));
                }
            }
            // 4、资源关闭
            inStream.close();
            outStream.close();
            socket.close();
            System.out.println("socket-client，get exit command");
        }
    }
    复制代码

测试结果：整个流程在没有收到客户端的`exit`退出指令前，会保持连接的状态，并且可以基于字节流模式，进行持续的数据传输；

![format_png 4][]

### 4、字符流使用 ###

基于上述的基础案例，采用字符流的方式进行数据传输，客户端和服务端只进行一次简单的交互；

-- 1、客户端
    BufferedReader bufReader = new BufferedReader(new InputStreamReader(inStream));
    BufferedWriter bufWriter = new BufferedWriter(new OutputStreamWriter(outStream));
    // 客户端发送数据
    bufWriter.write("hello,server");
    bufWriter.newLine();
    bufWriter.flush();
    // 客户端接收数据
    System.out.println("client-read："+bufReader.readLine());
    
    -- 2、服务端
    BufferedReader bufReader = new BufferedReader(new InputStreamReader(inStream));
    BufferedWriter bufWriter = new BufferedWriter(new OutputStreamWriter(outStream));
    // 服务端接收数据
    System.out.println("server-read："+bufReader.readLine());
    // 服务端响应数据
    bufWriter.write("hello,client");
    bufWriter.newLine();
    bufWriter.flush();
    复制代码

### 5、文件传输 ###

基于上述的基础案例，客户端向服务端发送图片文件，服务端完成文件的读取和保存，在处理完成后给客户端发送结果描述；

-- 1、客户端
    // 客户端发送图片
    FileInputStream fileStream = new FileInputStream("Local_File_Path/jvm.png");
    byte[] bytes = new byte[1024];
    int i = 0;
    while ((i = fileStream.read(bytes)) != -1) {
        outStream.write(bytes);
    }
    // 写入结束标记，禁用此套接字的输出流，之后再使用输出流会抛异常
    socket.shutdownOutput();
    // 接收服务端响应结果
    System.out.println("server-resp："+new String(bytes,0,readLen));
    
    -- 2、服务端
    // 接收客户端图片
    FileOutputStream fileOutputStream = new FileOutputStream("Local_File_Path/new_jvm.png");
    byte[] bytes = new byte[1024];
    int i = 0;
    while ((i = inStream.read(bytes)) != -1) {
        fileOutputStream.write(bytes, 0, i);
    }
    // 响应客户端文件处理结果
    outStream.write("file-save-success".getBytes());
    复制代码

### 6、TCP协议 ###

Socket网络编程是基于TCP协议的，TCP传输控制协议是一种面向连接的、可靠的、基于字节流的传输层通信协议，在上述案例中侧重基于流的数据传输，其中关于连接还涉及两个核心概念：

![format_png 5][]

**三次握手**：建立连接的过程，在这个过程中进行了三次网络通信，当连接处于建立的状态，就可以进行正常的通信，即数据传输；**四次挥手**：关闭连接的过程，调用`close`方法，即连接使用结束，在这个过程中进行了四次网络通信；

## 四、Http组件 ##

在服务通信时依赖网络，而对于编程来说，更常见的是的Http的组件，在微服务架构中，涉及到Http组件工具有很多，例如Spring框架中的RestTemplate，Feign框架支持ApacheHttp和OkHttp；下面围绕几个常用的组件编写测试案例；

### 1、基础接口 ###

@RestController
    public class BizWeb {
    
        @GetMapping("/getApi/{id}")
        public Rep<Integer> getApi(@PathVariable Integer id){
            log.info("id={}",id);
            return Rep.ok(id) ;
        }
    
        @GetMapping("/getApi_v2/{id}")
        public Rep<Integer> getApiV2(HttpServletRequest request,
                                     @PathVariable Integer id,
                                     @RequestParam("name") String name){
            String token = request.getHeader("Token");
            log.info("token={},id={},name={}",token,id,name);
            return Rep.ok(id) ;
        }
    
        @PostMapping("/postApi")
        public Rep<IdKey> postApi(HttpServletRequest request,@RequestBody IdKey idKey){
            String token = request.getHeader("Token");
            log.info("token={},idKey={}", token,JSONUtil.toJsonStr(idKey));
            return Rep.ok(idKey) ;
        }
    
        @PutMapping("/putApi")
        public Rep<IdKey> putApi(@RequestBody IdKey idKey){
            log.info("idKey={}", JSONUtil.toJsonStr(idKey));
            return Rep.ok(idKey) ;
        }
    
        @DeleteMapping("/delApi/{id}")
        public Rep<Integer> delApi(@PathVariable Integer id){
            log.info("id={}",id);
            return Rep.ok(id) ;
        }
    }
    复制代码

### 2、ApacheHttp ###

public class TestApacheHttp {
    
        private static final String BASE_URL = "http://localhost:8083" ;
        public static void main(String[] args) {
            BasicHeader header = new BasicHeader("Token","ApacheSup") ;
    
            // 1、发送Get请求
            Map<String,String> param = new HashMap<>() ;
            param.put("name","cicada") ;
            Rep getRep = doGet(BASE_URL+"/getApi_v2/3",header,param, Rep.class);
            System.out.println("get："+getRep);
    
            // 2、发送Post请求
            IdKey postBody = new IdKey(1,"id-key-我") ;
            Rep postRep = doPost (BASE_URL+"/postApi", header, postBody, Rep.class);
            System.out.println("post："+postRep);
        }
        /**
         * 构建HttpClient对象
         */
        private static CloseableHttpClient buildHttpClient (){
            // 请求配置
            RequestConfig reqConfig = RequestConfig.custom().setConnectTimeout(6000).build();
            return HttpClients.custom()
                    .setDefaultRequestConfig(reqConfig).build();
        }
        /**
         * 执行Get请求
         */
        public static <T> T doGet (String url, Header header, Map<String,String> param,
                                   Class<T> repClass) {
            // 创建Get请求
            CloseableHttpClient httpClient = buildHttpClient();
            HttpGet httpGet = new HttpGet();
            httpGet.addHeader(header);
            try {
                URIBuilder builder = new URIBuilder(url);
                if (param != null) {
                    for (String key : param.keySet()) {
                        builder.addParameter(key, param.get(key));
                    }
                }
                httpGet.setURI(builder.build());
                // 请求执行
                HttpResponse httpResponse = httpClient.execute(httpGet);
                if (httpResponse.getStatusLine().getStatusCode() == 200) {
                    // 结果转换
                    String resp = EntityUtils.toString(httpResponse.getEntity());
                    return JSONUtil.toBean(resp, repClass);
                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                IoUtil.close(httpClient);
            }
            return null;
        }
        /**
         * 执行Post请求
         */
        public static <T> T doPost (String url, Header header, Object body,Class<T> repClass) {
            // 创建Post请求
            CloseableHttpClient httpClient = buildHttpClient();
            HttpPost httpPost = new HttpPost(url);
            httpPost.addHeader(header);
            StringEntity conBody = new StringEntity(JSONUtil.toJsonStr(body),ContentType.APPLICATION_JSON);
            httpPost.setEntity(conBody);
            try {
                // 请求执行
                HttpResponse httpResponse = httpClient.execute(httpPost);
                if (httpResponse.getStatusLine().getStatusCode() == 200) {
                    // 结果转换
                    String resp = EntityUtils.toString(httpResponse.getEntity());
                    return JSONUtil.toBean(resp, repClass);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }finally {
                IoUtil.close(httpClient);
            }
            return null;
        }
    }
    复制代码

### 3、OkHttp ###

public class TestOkHttp {
    
        private static final String BASE_URL = "http://localhost:8083" ;
        public static void main(String[] args) {
            Headers headers = new Headers.Builder().add("Token","OkHttpSup").build() ;
    
            // 1、发送Get请求
            Rep getRep = execute(BASE_URL+"/getApi/1", Method.GET.name(), headers, null, Rep.class);
            System.out.println("get："+getRep);
    
            // 2、发送Post请求
            IdKey postBody = new IdKey(1,"id-key") ;
            Rep postRep = execute(BASE_URL+"/postApi", Method.POST.name(), headers, buildBody(postBody), Rep.class);
            System.out.println("post："+postRep);
    
            // 3、发送Put请求
            IdKey putBody = new IdKey(2,"key-id") ;
            Rep putRep = execute(BASE_URL+"/putApi", Method.PUT.name(), headers, buildBody(putBody), Rep.class);
            System.out.println("put："+putRep);
    
            // 4、发送Delete请求
            Rep delRep = execute(BASE_URL+"/delApi/2", Method.DELETE.name(), headers, null, Rep.class);
            System.out.println("del："+delRep);
        }
        /**
         * 构建JSON请求体
         */
        public static RequestBody buildBody (Object body){
            MediaType mediaType = MediaType.parse("application/json; charset=utf-8");
            return RequestBody.create(mediaType, JSONUtil.toJsonStr(body)) ;
        }
        /**
         * 构建OkHttpClient对象
         */
        public static OkHttpClient buildOkHttp () {
            return new OkHttpClient.Builder()
                    .readTimeout(10, TimeUnit.SECONDS).connectTimeout(6, TimeUnit.SECONDS)
                    .connectionPool(new ConnectionPool(15, 5, TimeUnit.SECONDS))
                    .build();
        }
        /**
         * 执行请求
         */
        public static <T> T execute (String url, String method,
                                     Headers headers, RequestBody body,
                                     Class<T> repClass) {
            // 请求创建
            OkHttpClient httpClient = buildOkHttp() ;
            Request.Builder requestBuild = new Request.Builder()
                    .url(url).method(method, body);
            if (headers != null) {
                requestBuild.headers(headers);
            }
            try  {
                // 请求执行
                Response response = httpClient.newCall(requestBuild.build()).execute();
                // 结果转换
                InputStream inStream = null;
                if (response.isSuccessful()) {
                    ResponseBody responseBody = response.body();
                    if (responseBody != null) {
                        inStream = responseBody.byteStream();
                    }
                }
                if (inStream != null) {
                    try {
                        byte[] respByte = IoUtil.readBytes(inStream);
                        if (respByte != null) {
                            return JSONUtil.toBean(new String(respByte, Charset.defaultCharset()), repClass);
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    } finally {
                        IoUtil.close(inStream);
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
            return null;
        }
    }
    复制代码

### 4、RestTemplate ###

public class TestRestTemplate {
    
        private static final String BASE_URL = "http://localhost:8083" ;
        public static void main(String[] args) {
    
            RestTemplate restTemplate = buildRestTemplate() ;
            // 1、发送Get请求
            Map<String,String> paramMap = new HashMap<>() ;
            Rep getRep = restTemplate.getForObject(BASE_URL+"/getApi/1",Rep.class,paramMap);
            System.out.println("get："+getRep);
    
            // 2、发送Post请求
            IdKey idKey = new IdKey(1,"id-key") ;
            Rep postRep = restTemplate.postForObject(BASE_URL+"/postApi",idKey,Rep.class);
            System.out.println("post："+postRep);
    
            // 3、发送Put请求
            IdKey idKey2 = new IdKey(2,"key-id") ;
            restTemplate.put(BASE_URL+"/putApi",idKey2,paramMap);
    
            // 4、发送Delete请求
            restTemplate.delete(BASE_URL+"/delApi/2",paramMap);
    
            // 5、自定义Header请求
            HttpHeaders headers = new HttpHeaders();
            headers.add("Token","AdminSup");
            HttpEntity<IdKey> requestEntity = new HttpEntity<>(idKey, headers);
            ResponseEntity<Rep> respEntity = restTemplate.exchange(BASE_URL+"/postApi",
                                                HttpMethod.POST, requestEntity, Rep.class);
            System.out.println("post-header："+respEntity.getBody());
        }
    
        private static RestTemplate buildRestTemplate (){
            // 1、参数配置
            SimpleClientHttpRequestFactory factory = new SimpleClientHttpRequestFactory();
            factory.setReadTimeout(3000);
            factory.setConnectTimeout(6000);
            // 2、创建对象
            return new RestTemplate(factory) ;
        }
    }

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