集合

List<Integer> list = List.of(10, 11, 12);
System.out.println(list);
// list為不可變集合，不能新增新元素

// 集合轉陣列
Integer[] num1 = list.toArray(new Integer[0]); // JDK 11 之前
Integer[] num2 = list.toArray(Integer[]::new); // JDK 11 之後

檔案

Files.writeString(Path.of("test1.txt"), "JDK11檔案輸出測試");
String content = Files.readString(Path.of("test1.txt"));
System.out.println(content);
 

try (
        InputStream in = new FileInputStream("test1.txt");
        OutputStream out = new FileOutputStream("test2.txt");
) {
    in.transferTo(out); // 輸入流轉輸出流
} catch (Exception e) {
    e.printStackTrace();
}

HttpClient

• 傳送同步請求

String url = "http://localhost:8090/learn/test";
// 1、建立一個HttpClient物件
HttpClient httpClient = HttpClient.newHttpClient();
// 2、建立一個http請求物件；request
HttpRequest request = HttpRequest.newBuilder()
        .uri(URI.create(url))
        .GET()
        .build();
// 3、發起request請求，獲取響應物件
HttpResponse<String> response = httpClient.send(request, HttpResponse.BodyHandlers.ofString());
// 4、獲取響應碼
int code = response.statusCode();
// 5、獲取響應結果資料
String result = response.body();
System.out.println("響應碼：" + code + "，響應結果：" + result);
 

• 傳送非同步請求

String url = "http://localhost:8090/learn/test";
// 1、建立一個HttpClient物件
HttpClient httpClient = HttpClient.newHttpClient();
// 2、建立一個http請求物件；request，預設是get請求
HttpRequest request = HttpRequest.newBuilder()
        .uri(URI.create(url))
        .GET()
        .build();
// 3、發起request非同步請求
CompletableFuture<HttpResponse<String>> future =
        httpClient.sendAsync(request, HttpResponse.BodyHandlers.ofString());
// 4、非同步：監聽結果資料
future.whenComplete( (stringHttpResponse, throwable) -> {
        // 5、處理結果資料
        if (throwable != null) { // 請求出錯了
            throwable.printStackTrace();
        } else {
            int code = stringHttpResponse.statusCode();
            String result = stringHttpResponse.body();
            System.out.println("響應碼：" + code + "，響應結果：" + result);
        }
    }).join(); // 阻塞程式（測試使用）
System.out.println("結束程式");