HOWTO · Java
用 Java 发送 HTTP 请求
本教程演示如何在 Java 中发送 HTTP 请求。
本页内容
我们可以使用 Java HttpURLConnection 和 Apache HttpClient 在 Java 中发送 HTTP 请求。本教程将演示如何使用 Java 中的两种方法发送 HTTP 请求。
在 Java 中使用 HttpURLConnection 发送 HTTP 请求
HttpURLConnection 是来自 Java.net 库的内置方法。HTTP 请求有两种类型，GET 和 POST。
让我们尝试使用 HttpURLConnection 发送两者。
在 Java 中使用 HttpURLConnection 发送 GET HTTP 请求
让我们尝试使用 GET 方法 HttpURLConnection 方法来获取我们网页的内容。
例子：
package delftstack;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
public class Get_HttpURLConnection {
private static HttpURLConnection get_connection;
public static void main(String[] args) throws IOException {
String url = "https://www.delftstack.com/";
try {
// We retrieve the contents of our webpage.
URL myurl = new URL(url);
get_connection = (HttpURLConnection) myurl.openConnection();
// Here we specify the connection type
get_connection.setRequestMethod("GET");
StringBuilder webpage_content;
try (BufferedReader webpage =
new BufferedReader(new InputStreamReader(get_connection.getInputStream()))) {
String webpage_line;
webpage_content = new StringBuilder();
while ((webpage_line = webpage.readLine()) != null) {
webpage_content.append(webpage_line);
webpage_content.append(System.lineSeparator());
}
}
System.out.println(webpage_content.toString());
} finally {
// Disconnect the connection
get_connection.disconnect();
}
}
}
上面的代码会从 https://www.delftstack.com/ 输出大量内容。
输出：
在 Java 中使用 HttpURLConnection 发送 POST HTTP 请求
要使用 HttpURLConnection 通过 POST 方法发送 HTTP 请求，我们必须设置请求属性。下面的示例演示了通过 HttpURLConnection 和 POST 方法发送 HTTP 请求，需要 URL 和 URL 参数。
package delftstack;
import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.charset.StandardCharsets;
public class POST_HttpURLConnection {
private static HttpURLConnection post_connection;
public static void main(String[] args) throws IOException {
// URL
String Post_URL = "https://httpbin.org/post";
// URL Parameters
String Post_URL_Parameters = "name=Michelle&occupation=Secretory";
// Get Bytes of parameters
byte[] Post_Data = Post_URL_Parameters.getBytes(StandardCharsets.UTF_8);
try {
URL Demo_URL = new URL(Post_URL);
post_connection = (HttpURLConnection) Demo_URL.openConnection();
post_connection.setDoOutput(true);
// Set the method
post_connection.setRequestMethod("POST");
// The request property
post_connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
// write the bytes or the data to the URL connection.
try (DataOutputStream Data_Output_Stream =
new DataOutputStream(post_connection.getOutputStream())) {
Data_Output_Stream.write(Post_Data);
}
// Get the content
StringBuilder Post_Webpage_Content;
try (BufferedReader webpage =
new BufferedReader(new InputStreamReader(post_connection.getInputStream()))) {
String Webpage_line;
Post_Webpage_Content = new StringBuilder();
while ((Webpage_line = webpage.readLine()) != null) {
Post_Webpage_Content.append(Webpage_line);
Post_Webpage_Content.append(System.lineSeparator());
}
}
System.out.println(Post_Webpage_Content.toString());
} finally {
post_connection.disconnect();
}
}
}
输出：
{
"args": {},
"data": "",
"files": {},
"form": {
"name": "Michelle",
"occupation": "Secretory"
},
"headers": {
"Accept": "text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2",
"Content-Length": "34",
"Content-Type": "application/x-www-form-urlencoded",
"Host": "httpbin.org",
"User-Agent": "Java/17.0.2",
"X-Amzn-Trace-Id": "Root=1-62308f8e-7aa124b15d6d3cd1114d6463"
},
"json": null,
"origin": "182.182.126.98",
"url": "https://httpbin.org/post"
}
在 Java 中使用 Apache HttpClient 来发送 HTTP 请求
要首先使用 Apache HttpClient，你必须将库添加到你的项目下载 Apache HttpClient 并将 jar 文件添加到你的项目构建路径库中。
在 Java 中使用 Apache HttpClient 发送 GET HTTP 请求
我们也可以使用 Apache HttpClient 并通过 GET 方法发送 HTTP 请求来获取内容。Apache HttpClient 比 HttpURLConnection 更容易。
例子：
package delftstack;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
public class Get_HttpClient {
public static void main(String[] args) throws IOException {
try (CloseableHttpClient Apache_Get_Client = HttpClientBuilder.create().build()) {
// Create a GET request
HttpGet Apache_Get_Request = new HttpGet("https://www.delftstack.com/");
// execute the request to get the response
HttpResponse Apache_Get_Response = Apache_Get_Client.execute(Apache_Get_Request);
// Get the content
BufferedReader Webpage =
new BufferedReader(new InputStreamReader(Apache_Get_Response.getEntity().getContent()));
StringBuilder Webpage_Content = new StringBuilder();
String Webpage_Content_Line;
while ((Webpage_Content_Line = Webpage.readLine()) != null) {
Webpage_Content.append(Webpage_Content_Line);
Webpage_Content.append(System.lineSeparator());
}
System.out.println(Webpage_Content);
}
}
}
输出：
在 Java 中使用 Apache HttpClient 发送 POST HTTP 请求
我们可以使用 Apache HttpClient 并通过 POST 方法发送 HTTP 请求来获取内容。
例子：
package delftstack;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
public class Post_HttpClient {
public static void main(String[] args) throws IOException {
try (CloseableHttpClient Apache_Post_Client = HttpClientBuilder.create().build()) {
// Create a post request
HttpPost Apache_Post_Request = new HttpPost("https://www.delftstack.com/");
// pass parameters or set entity
Apache_Post_Request.setEntity(new StringEntity("This is delftstack"));
// execute the request to get the response
HttpResponse Apache_Post_Response = Apache_Post_Client.execute(Apache_Post_Request);
// Get the content
BufferedReader Webpage =
new BufferedReader(new InputStreamReader(Apache_Post_Response.getEntity().getContent()));
StringBuilder Webpage_Content = new StringBuilder();
String Webpage_line;
while ((Webpage_line = Webpage.readLine()) != null) {
Webpage_Content.append(Webpage_line);
Webpage_Content.append(System.lineSeparator());
}
System.out.println(Webpage_Content);
}
}
}
输出：
Java 11 及之前的版本具有 HttpClient 的内置功能，新版本不支持该功能。HttpClient 与 Apache HTTPClient 不同。
