java发起网络请求远程服务

<think>我们被要求提供Java发起网络请求调用远程服务的示例代码。根据引用内容，我们可以使用Java内置的HttpURLConnection或第三方库如OkHttp。下面将分别展示这两种方式。###方法1：使用Java内置的HttpURLConnection（适用于简单请求）```javaimportjava.io.BufferedReader;importjava.io.InputStream;importjava.io.InputStreamReader;importjava.net.HttpURLConnection;importjava.net.URL;publicclassHttpExample{publicstaticvoidmain(String[]args){try{//1.创建URL对象URLurl=newURL("http://example.com/api");//2.打开连接HttpURLConnectionconnection=(HttpURLConnection)url.openConnection();//3.设置请求方法（GET/POST等）connection.setRequestMethod("GET");//4.设置连接和读取超时（单位：毫秒）connection.setConnectTimeout(5000);connection.setReadTimeout(5000);//5.可选：设置请求头connection.setRequestProperty("User-Agent","Mozilla/5.0");connection.setRequestProperty("Accept","application/json");//6.建立连接connection.connect();//7.获取响应码intresponseCode=connection.getResponseCode();System.out.println("ResponseCode:"+responseCode);//8.读取响应内容（成功时）if(responseCode==HttpURLConnection.HTTP_OK){InputStreaminputStream=connection.getInputStream();BufferedReaderreader=newBufferedReader(newInputStreamReader(inputStream));Stringline;StringBuilderresponse=newStringBuilder();while((line=reader.readLine())!=null){response.append(line);}reader.close();System.out.println("Response:"+response.toString());}else{System.out.println("Requestfailed");}//9.断开连接connection.disconnect();}catch(Exceptione){e.printStackTrace();}}}```###方法2：使用OkHttp（推荐，更简洁高效）首先添加OkHttp依赖（Maven）：```xml<dependency><groupId>com.squareup.okhttp3</groupId><artifactId>okhttp</artifactId><version>4.9.3</version></dependency>```示例代码：```javaimportokhttp3.OkHttpClient;importokhttp3.Request;importokhttp3.Response;publicclassOkHttpExample{publicstaticvoidmain(String[]args){OkHttpClientclient=newOkHttpClient();Requestrequest=newRequest.Builder().url("http://example.com/api").get().addHeader("User-Agent","OkHttpExample").build();try(Responseresponse=client.newCall(request).execute()){if(response.isSuccessful()&&response.body()!=null){System.out.println("Response:"+response.body().string());}else{System.out.println("Requestfailed:"+response.code());}}catch(Exceptione){e.printStackTrace();}}}```###POST请求示例（使用OkHttp发送JSON数据）```javaimportokhttp3.*;publicclassOkHttpPostExample{publicstaticvoidmain(String[]args){OkHttpClientclient=newOkHttpClient();MediaTypeJSON=MediaType.parse("application/json;charset=utf-8");StringjsonBody="{\"name\":\"John\",\"age\":30}";RequestBodybody=RequestBody.create(jsonBody,JSON);Requestrequest=newRequest.Builder().url("http://example.com/api/post").post(body).addHeader("Content-Type","application/json").build();try(Responseresponse=client.newCall(request).execute()){System.out.println(response.body().string());}catch(Exceptione){e.printStackTrace();}}}```###关键说明1.**请求方法**：通过`setRequestMethod()`（HttpURLConnection）或`.get()/.post()`（OkHttp）设置2.**超时控制**：HttpURLConnection使用`setConnectTimeout()`和`setReadTimeout()`，OkHttp通过`OkHttpClient.Builder()`配置3.**请求头**：使用`setRequestProperty()`（HttpURLConnection）或`addHeader()`（OkHttp）4.**异常处理**：网络请求必须捕获`IOException`5.**资源释放**：确保关闭输入流和断开连接（HttpURLConnection）或使用try-with-resources（OkHttp）###注意事项-生产环境中建议使用连接池和超时配置优化性能-处理HTTPS时需要配置SSL（OkHttp默认支持）-大文件下载建议使用流式传输避免内存溢出###相关问题1.如何用Java实现异步HTTP请求？2.如何处理HTTP请求中的重定向？3.如何用Java发送带文件上传的POST请求？4.OkHttp和HttpClient哪个性能更好？[^1]:[OkHttp官方网站](https://square.github.io/okhttp/)[^2]:[Java官方HttpURLConnection文档](https://docs.oracle.com/javase/8/docs/api/java/net/HttpURLConnection.html)</think>### Java 发起网络请求调用远程服务示例代码 在 Java 中发起网络请求主要有三种主流方式：原生 `HttpURLConnection`、Apache HttpClient 和 OkHttp。以下是详细示例： --- ### 1. 使用原生 HttpURLConnection (Java 标准库) ```java import java.io.*; import java.net.*; public class HttpURLConnectionExample { public static void main(String[] args) { String url = "https://api.example.com/data"; try { // 1. 创建连接 URL apiUrl = new URL(url); HttpURLConnection conn = (HttpURLConnection) apiUrl.openConnection(); // 2. 设置请求方法 conn.setRequestMethod("GET"); // 3. 设置请求头 conn.setRequestProperty("Content-Type", "application/json"); conn.setRequestProperty("Authorization", "Bearer your_token"); // 4. 设置超时时间（毫秒） conn.setConnectTimeout(5000); conn.setReadTimeout(10000); // 5. 获取响应 int status = conn.getResponseCode(); if (status == 200) { // HTTP_OK try (BufferedReader reader = new BufferedReader( new InputStreamReader(conn.getInputStream()))) { StringBuilder response = new StringBuilder(); String line; while ((line = reader.readLine()) != null) { response.append(line); } System.out.println("响应结果: " + response.toString()); } } else { System.err.println("请求失败，状态码: " + status); } // 6. 关闭连接 conn.disconnect(); } catch (Exception e) { e.printStackTrace(); } } } ``` --- ### 2. 使用 Apache HttpClient (Maven依赖) ```xml <dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpclient</artifactId> <version>4.5.13</version> </dependency> ``` ```java import org.apache.http.client.methods.*; import org.apache.http.impl.client.*; import org.apache.http.util.EntityUtils; public class HttpClientExample { public static void main(String[] args) { String url = "https://api.example.com/data"; try (CloseableHttpClient httpClient = HttpClients.createDefault()) { // 1. 创建GET请求 HttpGet request = new HttpGet(url); // 2. 设置请求头 request.setHeader("Content-Type", "application/json"); request.setHeader("Authorization", "Bearer your_token"); // 3. 执行请求 try (CloseableHttpResponse response = httpClient.execute(request)) { int status = response.getStatusLine().getStatusCode(); if (status == 200) { String result = EntityUtils.toString(response.getEntity()); System.out.println("响应结果: " + result); } else { System.err.println("请求失败，状态码: " + status); } } } catch (Exception e) { e.printStackTrace(); } } } ``` --- ### 3. 使用 OkHttp (推荐，Maven依赖) ```xml <dependency> <groupId>com.squareup.okhttp3</groupId> <artifactId>okhttp</artifactId> <version>4.9.3</version> </dependency> ``` ```java import okhttp3.*; public class OkHttpExample { public static void main(String[] args) { String url = "https://api.example.com/data"; OkHttpClient client = new OkHttpClient(); // 1. 创建请求 Request request = new Request.Builder() .url(url) .header("Content-Type", "application/json") .header("Authorization", "Bearer your_token") .build(); // 2. 发送请求 try (Response response = client.newCall(request).execute()) { if (response.isSuccessful()) { String result = response.body().string(); System.out.println("响应结果: " + result); } else { System.err.println("请求失败，状态码: " + response.code()); } } catch (Exception e) { e.printStackTrace(); } } } ``` --- ### POST 请求示例 (使用 OkHttp) ```java // 创建 JSON 请求体 String json = "{\"name\":\"John\", \"age\":30}"; RequestBody body = RequestBody.create(json, MediaType.parse("application/json")); Request postRequest = new Request.Builder() .url("https://api.example.com/submit") .post(body) // 设置 POST 方法 .build(); try (Response response = client.newCall(postRequest).execute()) { // 处理响应... } ``` --- ### 关键注意事项 1. **异常处理**：网络请求必须处理 `IOException` 2. **资源释放**：确保关闭连接和响应资源（使用 try-with-resources） 3. **超时设置**： ```java // OkHttp 超时配置 OkHttpClient client = new OkHttpClient.Builder() .connectTimeout(10, TimeUnit.SECONDS) .readTimeout(30, TimeUnit.SECONDS) .build(); ``` 4. **HTTPS 支持**：所有现代库都支持 HTTPS，无需额外配置 5. **性能对比**： - `HttpURLConnection`：标准库，无需依赖 - Apache HttpClient：功能最全面 - OkHttp：性能最优，现代应用首选[^1] --- ### 相关问题 1. 如何处理 HTTP 请求的异步调用？ 2. 如何用 Java 实现文件上传的 POST 请求？ 3. 网络请求中如何正确处理重定向？ 4. 如何为 Java 网络请求添加重试机制？ 5. 不同 HTTP 客户端库的性能对比指标有哪些？ [^1]: [OkHttp 官方文档](https://square.github.io/okhttp/) [^2]: [Java 官方网络编程文档](https://docs.oracle.com/javase/tutorial/networking/)