开发

你可能已经迫不及待想安装 Java，写个 Java 程序跑起来了。但是在这之前，有些概念需要提前了解，因为 Java 跟 C、C++和 Python 都有点不一样。

本书作者：测试开发刚哥，文章版权归个人所有，未经授权请勿转载。 Servlet 生命周期 Servlet 的生命周期由 Servlet 容器（如 Tomcat、Jetty 等）管理，主要包括以下 5 个阶段： 加载 Servlet 类 创建 Servlet 实例 调用 init 方法 调用 service 方法 调用 destroy 方法 加载（Loading）： 当 Servlet 容器启动或第一次接收到对某个 Servlet 的请求时，它会加载 Servlet 类 这个过程只发生一次，除非 Servlet 被卸载或容器重新启动 实例化（Instantiation）： 在加载 Servlet 类之后，容器会创建一个 Servlet 实例 这个实例化过程也是一次性的，除非 Servlet 被卸载或容器重新启动 初始化（Initialization）： 容器调用 Servlet 实例的init()方法进行初始化 init()方法只被调用一次，用于执行一次性的初始化任务，如读取配置参数、初始化资源等 你可以重写init()方法以执行自定义的初始化逻辑 public void init(ServletConfig config) 请求处理（Request Handling）： 每当有请求到达时，容器会调用 Servlet 的service()方法来处理请求 service()方法根据请求的类型（如 GET、POST 等）调用相应的处理方法（如doGet()、doPost()等） public void service(ServletRequest request, ServletResponse response) 销毁（Destruction）： 当容器决定卸载 Servlet（如容器关闭或 Servlet 被重新加载）时，它会调用 Servlet 的destroy()方法 destroy()方法用于执行清理任务，如关闭资源、保存状态等 destroy()方法只被调用一次 public void destroy() ...

本书作者：测试开发刚哥，文章版权归个人所有，未经授权请勿转载。 OkHttp 是什么 OkHttp 是一个 HTTP 客户端，它不只是简单的发送请求和接收响应，还包含了失败重试、响应缓存等特性功能，并且能支持同步和异步请求。 OkHttp 的语法相当简洁，比如 Get： OkHttpClient client = new OkHttpClient(); String run(String url) throws IOException { Request request = new Request.Builder() .url(url) .build(); try (Response response = client.newCall(request).execute()) { return response.body().string(); } } 比如 Post： public static final MediaType JSON = MediaType.get("application/json; charset=utf-8"); OkHttpClient client = new OkHttpClient(); String post(String url, String json) throws IOException { RequestBody body = RequestBody.create(json, JSON); Request request = new Request.Builder() .url(url) .post(body) .build(); try (Response response = client.newCall(request).execute()) { return response.body().string(); } } 常见用法 Get（同步） private final OkHttpClient client = new OkHttpClient(); public void run() throws Exception { Request request = new Request.Builder() .url("https://publicobject.com/helloworld.txt") .build(); try (Response response = client.newCall(request).execute()) { if (!response.isSuccessful()) throw new IOException("Unexpected code " + response); Headers responseHeaders = response.headers(); for (int i = 0; i < responseHeaders.size(); i++) { System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i)); } System.out.println(response.body().string()); } } Get（异步） private final OkHttpClient client = new OkHttpClient(); public void run() throws Exception { Request request = new Request.Builder() .url("http://publicobject.com/helloworld.txt") .build(); client.newCall(request).enqueue(new Callback() { @Override public void onFailure(Call call, IOException e) { e.printStackTrace(); } @Override public void onResponse(Call call, Response response) throws IOException { try (ResponseBody responseBody = response.body()) { if (!response.isSuccessful()) throw new IOException("Unexpected code " + response); Headers responseHeaders = response.headers(); for (int i = 0, size = responseHeaders.size(); i < size; i++) { System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i)); } System.out.println(responseBody.string()); } } }); } 访问 Header private final OkHttpClient client = new OkHttpClient(); public void run() throws Exception { Request request = new Request.Builder() .url("https://api.github.com/repos/square/okhttp/issues") .header("User-Agent", "OkHttp Headers.java") .addHeader("Accept", "application/json; q=0.5") .addHeader("Accept", "application/vnd.github.v3+json") .build(); try (Response response = client.newCall(request).execute()) { if (!response.isSuccessful()) throw new IOException("Unexpected code " + response); System.out.println("Server: " + response.header("Server")); System.out.println("Date: " + response.header("Date")); System.out.println("Vary: " + response.headers("Vary")); } } Post JSON public static final MediaType JSON = MediaType.get("application/json; charset=utf-8"); OkHttpClient client = new OkHttpClient(); String post(String url, String json) throws IOException { RequestBody body = RequestBody.create(json, JSON); Request request = new Request.Builder() .url(url) .post(body) .build(); try (Response response = client.newCall(request).execute()) { return response.body().string(); } } Post 字符串 public static final MediaType MEDIA_TYPE_MARKDOWN = MediaType.parse("text/x-markdown; charset=utf-8"); private final OkHttpClient client = new OkHttpClient(); public void run() throws Exception { String postBody = "" + "Releases\n" + "--------\n" + "\n" + " * _1.0_ May 6, 2013\n" + " * _1.1_ June 15, 2013\n" + " * _1.2_ August 11, 2013\n"; Request request = new Request.Builder() .url("https://api.github.com/markdown/raw") .post(RequestBody.create(MEDIA_TYPE_MARKDOWN, postBody)) .build(); try (Response response = client.newCall(request).execute()) { if (!response.isSuccessful()) throw new IOException("Unexpected code " + response); System.out.println(response.body().string()); } } Post Streaming public static final MediaType MEDIA_TYPE_MARKDOWN = MediaType.parse("text/x-markdown; charset=utf-8"); private final OkHttpClient client = new OkHttpClient(); public void run() throws Exception { RequestBody requestBody = new RequestBody() { @Override public MediaType contentType() { return MEDIA_TYPE_MARKDOWN; } @Override public void writeTo(BufferedSink sink) throws IOException { sink.writeUtf8("Numbers\n"); sink.writeUtf8("-------\n"); for (int i = 2; i <= 997; i++) { sink.writeUtf8(String.format(" * %s = %s\n", i, factor(i))); } } private String factor(int n) { for (int i = 2; i < n; i++) { int x = n / i; if (x * i == n) return factor(x) + " × " + i; } return Integer.toString(n); } }; Request request = new Request.Builder() .url("https://api.github.com/markdown/raw") .post(requestBody) .build(); try (Response response = client.newCall(request).execute()) { if (!response.isSuccessful()) throw new IOException("Unexpected code " + response); System.out.println(response.body().string()); } } Post 文件 public static final MediaType MEDIA_TYPE_MARKDOWN = MediaType.parse("text/x-markdown; charset=utf-8"); private final OkHttpClient client = new OkHttpClient(); public void run() throws Exception { File file = new File("README.md"); Request request = new Request.Builder() .url("https://api.github.com/markdown/raw") .post(RequestBody.create(MEDIA_TYPE_MARKDOWN, file)) .build(); try (Response response = client.newCall(request).execute()) { if (!response.isSuccessful()) throw new IOException("Unexpected code " + response); System.out.println(response.body().string()); } } Post parameters private final OkHttpClient client = new OkHttpClient(); public void run() throws Exception { RequestBody formBody = new FormBody.Builder() .add("search", "Jurassic Park") .build(); Request request = new Request.Builder() .url("https://en.wikipedia.org/w/index.php") .post(formBody) .build(); try (Response response = client.newCall(request).execute()) { if (!response.isSuccessful()) throw new IOException("Unexpected code " + response); System.out.println(response.body().string()); } } Post multipart /** * The imgur client ID for OkHttp recipes. If you're using imgur for anything other than running * these examples, please request your own client ID! https://api.imgur.com/oauth2 */ private static final String IMGUR_CLIENT_ID = "..."; private static final MediaType MEDIA_TYPE_PNG = MediaType.parse("image/png"); private final OkHttpClient client = new OkHttpClient(); public void run() throws Exception { // Use the imgur image upload API as documented at https://api.imgur.com/endpoints/image RequestBody requestBody = new MultipartBody.Builder() .setType(MultipartBody.FORM) .addFormDataPart("title", "Square Logo") .addFormDataPart("image", "logo-square.png", RequestBody.create(MEDIA_TYPE_PNG, new File("website/static/logo-square.png"))) .build(); Request request = new Request.Builder() .header("Authorization", "Client-ID " + IMGUR_CLIENT_ID) .url("https://api.imgur.com/3/image") .post(requestBody) .build(); try (Response response = client.newCall(request).execute()) { if (!response.isSuccessful()) throw new IOException("Unexpected code " + response); System.out.println(response.body().string()); } } 解析 JSON 响应为 Java 对象 private final OkHttpClient client = new OkHttpClient(); private final Moshi moshi = new Moshi.Builder().build(); private final JsonAdapter<Gist> gistJsonAdapter = moshi.adapter(Gist.class); public void run() throws Exception { Request request = new Request.Builder() .url("https://api.github.com/gists/c2a7c39532239ff261be") .build(); try (Response response = client.newCall(request).execute()) { if (!response.isSuccessful()) throw new IOException("Unexpected code " + response); Gist gist = gistJsonAdapter.fromJson(response.body().source()); for (Map.Entry<String, GistFile> entry : gist.files.entrySet()) { System.out.println(entry.getKey()); System.out.println(entry.getValue().content); } } } static class Gist { Map<String, GistFile> files; } static class GistFile { String content; } 响应缓存 private final OkHttpClient client; public CacheResponse(File cacheDirectory) throws Exception { int cacheSize = 10 * 1024 * 1024; // 10 MiB Cache cache = new Cache(cacheDirectory, cacheSize); client = new OkHttpClient.Builder() .cache(cache) .build(); } public void run() throws Exception { Request request = new Request.Builder() .url("http://publicobject.com/helloworld.txt") .build(); String response1Body; try (Response response1 = client.newCall(request).execute()) { if (!response1.isSuccessful()) throw new IOException("Unexpected code " + response1); response1Body = response1.body().string(); System.out.println("Response 1 response: " + response1); System.out.println("Response 1 cache response: " + response1.cacheResponse()); System.out.println("Response 1 network response: " + response1.networkResponse()); } String response2Body; try (Response response2 = client.newCall(request).execute()) { if (!response2.isSuccessful()) throw new IOException("Unexpected code " + response2); response2Body = response2.body().string(); System.out.println("Response 2 response: " + response2); System.out.println("Response 2 cache response: " + response2.cacheResponse()); System.out.println("Response 2 network response: " + response2.networkResponse()); } System.out.println("Response 2 equals Response 1? " + response1Body.equals(response2Body)); } 取消调用 private final ScheduledExecutorService executor = Executors.newScheduledThreadPool(1); private final OkHttpClient client = new OkHttpClient(); public void run() throws Exception { Request request = new Request.Builder() .url("http://httpbin.org/delay/2") // This URL is served with a 2 second delay. .build(); final long startNanos = System.nanoTime(); final Call call = client.newCall(request); // Schedule a job to cancel the call in 1 second. executor.schedule(new Runnable() { @Override public void run() { System.out.printf("%.2f Canceling call.%n", (System.nanoTime() - startNanos) / 1e9f); call.cancel(); System.out.printf("%.2f Canceled call.%n", (System.nanoTime() - startNanos) / 1e9f); } }, 1, TimeUnit.SECONDS); System.out.printf("%.2f Executing call.%n", (System.nanoTime() - startNanos) / 1e9f); try (Response response = call.execute()) { System.out.printf("%.2f Call was expected to fail, but completed: %s%n", (System.nanoTime() - startNanos) / 1e9f, response); } catch (IOException e) { System.out.printf("%.2f Call failed as expected: %s%n", (System.nanoTime() - startNanos) / 1e9f, e); } } 超时 private final OkHttpClient client; public ConfigureTimeouts() throws Exception { client = new OkHttpClient.Builder() .connectTimeout(10, TimeUnit.SECONDS) .writeTimeout(10, TimeUnit.SECONDS) .readTimeout(30, TimeUnit.SECONDS) .build(); } public void run() throws Exception { Request request = new Request.Builder() .url("http://httpbin.org/delay/2") // This URL is served with a 2 second delay. .build(); try (Response response = client.newCall(request).execute()) { System.out.println("Response completed: " + response); } } Per-call Configuration private final OkHttpClient client = new OkHttpClient(); public void run() throws Exception { Request request = new Request.Builder() .url("http://httpbin.org/delay/1") // This URL is served with a 1 second delay. .build(); // Copy to customize OkHttp for this request. OkHttpClient client1 = client.newBuilder() .readTimeout(500, TimeUnit.MILLISECONDS) .build(); try (Response response = client1.newCall(request).execute()) { System.out.println("Response 1 succeeded: " + response); } catch (IOException e) { System.out.println("Response 1 failed: " + e); } // Copy to customize OkHttp for this request. OkHttpClient client2 = client.newBuilder() .readTimeout(3000, TimeUnit.MILLISECONDS) .build(); try (Response response = client2.newCall(request).execute()) { System.out.println("Response 2 succeeded: " + response); } catch (IOException e) { System.out.println("Response 2 failed: " + e); } } 处理认证鉴权 private final OkHttpClient client; public Authenticate() { client = new OkHttpClient.Builder() .authenticator(new Authenticator() { @Override public Request authenticate(Route route, Response response) throws IOException { if (response.request().header("Authorization") != null) { return null; // Give up, we've already attempted to authenticate. } System.out.println("Authenticating for response: " + response); System.out.println("Challenges: " + response.challenges()); String credential = Credentials.basic("jesse", "password1"); return response.request().newBuilder() .header("Authorization", credential) .build(); } }) .build(); } public void run() throws Exception { Request request = new Request.Builder() .url("http://publicobject.com/secrets/hellosecret.txt") .build(); try (Response response = client.newCall(request).execute()) { if (!response.isSuccessful()) throw new IOException("Unexpected code " + response); System.out.println(response.body().string()); } } 跳过重试： ...

数学里面的加减乘除，就是运算符，但是 Python 的运算符更多样，更复杂，分为算术运算符、比较运算符、赋值运算符、位运算符、逻辑运算符、成员运算符、身份运算符。为了更直观的看到运算符的使用，本文采用代码和注释结合的方式进行讲解。

Spring Boot helps you to create stand-alone, production-grade Spring-based applications that you can run. Most Spring Boot applications need very little Spring configuration.

80 道高频算法题来源于牛客网，这些答案都经过了我验证，可以复制粘贴后提交通过：

Django 官方并没有提供标准的项目结构，于是网上众说纷纭，百花齐放，一千个读者有一千个哈姆雷特。那我们该怎么设计项目结构呢？在回答这个问题之前，先了解一下 Django 原生的目录和文件都是干嘛的。

Dockerfile是一个文本文件，包含一些 Docker 指令。执行docker build，Docker 就会执行Dockerfile里面的指令，来自动创建镜像。

Flask 有个特点：千人千面。它没有硬性规定，你必须采用哪种项目结构来组织代码，这就导致每个人都按照自己的习惯和喜好来写，写出来的项目结构往往是千差万别。在 Flask2.0 的官方文档中，有一节内容介绍了 Flask 的项目结构，我们可以窥探一番。

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