这里经常会问到java.net.URLConnection的使用，Oracle教程对此过于简洁。
该教程基本上只展示了如何发出GET请求并读取响应。它没有解释如何使用它来执行POST请求、设置请求头、读取响应头、处理cookie、提交HTML表单、上传文件等。
那么，我如何使用java.net.URLConnection来激发和处理“高级”HTTP请求？
当前回答
在使用HTTP时，引用HttpURLConnection而不是基类URLConnection几乎总是更有用（因为URLConnection是一个抽象类，当您在HTTP URL上请求URLConnection.openConnection（）时，无论如何都会返回）。
然后，您可以不依赖URLConnection#setDoOutput（true）将请求方法隐式设置为POST，而是使用httpURLConnection.setRequestMethod（“POST”），有些人可能会觉得这更自然（这也允许您指定其他请求方法，如PUT、DELETE…）。
它还提供了有用的HTTP常量，因此您可以执行以下操作：
int responseCode = httpURLConnection.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) {
其他回答
您还可以使用jcabi http（我是一名开发人员）的JdkRequest，它为您完成所有这些工作，装饰HttpURLConnection、激发http请求和解析响应，例如：
String html = new JdkRequest("http://www.google.com").fetch().body();
查看此日志以了解更多信息：http://www.yegor256.com/2014/04/11/jcabi-http-intro.html
还有OkHttp，它是一个默认高效的HTTP客户端：
HTTP/2支持允许对同一主机的所有请求共享一个套接字。连接池减少了请求延迟（如果HTTP/2不可用）。透明GZIP缩小了下载大小。响应缓存完全避免了重复请求的网络。
首先创建OkHttpClient的实例：
OkHttpClient client = new OkHttpClient();
然后，准备GET请求：
Request request = new Request.Builder()
.url(url)
.build();
最后，使用OkHttpClient发送准备好的请求：
Response response = client.newCall(request).execute();
有关详细信息，请参阅OkHttp的文档
我也受到了这个回应的启发。
我经常在需要做一些HTTP的项目中，我可能不想引入很多第三方依赖关系（这会引入其他依赖关系等等）
我开始根据这段对话编写我自己的实用程序（没有在任何地方完成）：
package org.boon.utils;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.util.Map;
import static org.boon.utils.IO.read;
public class HTTP {
然后就是一堆静态方法。
public static String get(
final String url) {
Exceptions.tryIt(() -> {
URLConnection connection;
connection = doGet(url, null, null, null);
return extractResponseString(connection);
});
return null;
}
public static String getWithHeaders(
final String url,
final Map<String, ? extends Object> headers) {
URLConnection connection;
try {
connection = doGet(url, headers, null, null);
return extractResponseString(connection);
} catch (Exception ex) {
Exceptions.handle(ex);
return null;
}
}
public static String getWithContentType(
final String url,
final Map<String, ? extends Object> headers,
String contentType) {
URLConnection connection;
try {
connection = doGet(url, headers, contentType, null);
return extractResponseString(connection);
} catch (Exception ex) {
Exceptions.handle(ex);
return null;
}
}
public static String getWithCharSet(
final String url,
final Map<String, ? extends Object> headers,
String contentType,
String charSet) {
URLConnection connection;
try {
connection = doGet(url, headers, contentType, charSet);
return extractResponseString(connection);
} catch (Exception ex) {
Exceptions.handle(ex);
return null;
}
}
然后发布。。。
public static String postBody(
final String url,
final String body) {
URLConnection connection;
try {
connection = doPost(url, null, "text/plain", null, body);
return extractResponseString(connection);
} catch (Exception ex) {
Exceptions.handle(ex);
return null;
}
}
public static String postBodyWithHeaders(
final String url,
final Map<String, ? extends Object> headers,
final String body) {
URLConnection connection;
try {
connection = doPost(url, headers, "text/plain", null, body);
return extractResponseString(connection);
} catch (Exception ex) {
Exceptions.handle(ex);
return null;
}
}
public static String postBodyWithContentType(
final String url,
final Map<String, ? extends Object> headers,
final String contentType,
final String body) {
URLConnection connection;
try {
connection = doPost(url, headers, contentType, null, body);
return extractResponseString(connection);
} catch (Exception ex) {
Exceptions.handle(ex);
return null;
}
}
public static String postBodyWithCharset(
final String url,
final Map<String, ? extends Object> headers,
final String contentType,
final String charSet,
final String body) {
URLConnection connection;
try {
connection = doPost(url, headers, contentType, charSet, body);
return extractResponseString(connection);
} catch (Exception ex) {
Exceptions.handle(ex);
return null;
}
}
private static URLConnection doPost(String url, Map<String, ? extends Object> headers,
String contentType, String charset, String body
) throws IOException {
URLConnection connection;/* Handle output. */
connection = new URL(url).openConnection();
connection.setDoOutput(true);
manageContentTypeHeaders(contentType, charset, connection);
manageHeaders(headers, connection);
IO.write(connection.getOutputStream(), body, IO.CHARSET);
return connection;
}
private static void manageHeaders(Map<String, ? extends Object> headers, URLConnection connection) {
if (headers != null) {
for (Map.Entry<String, ? extends Object> entry : headers.entrySet()) {
connection.setRequestProperty(entry.getKey(), entry.getValue().toString());
}
}
}
private static void manageContentTypeHeaders(String contentType, String charset, URLConnection connection) {
connection.setRequestProperty("Accept-Charset", charset == null ? IO.CHARSET : charset);
if (contentType!=null && !contentType.isEmpty()) {
connection.setRequestProperty("Content-Type", contentType);
}
}
private static URLConnection doGet(String url, Map<String, ? extends Object> headers,
String contentType, String charset) throws IOException {
URLConnection connection;/* Handle output. */
connection = new URL(url).openConnection();
manageContentTypeHeaders(contentType, charset, connection);
manageHeaders(headers, connection);
return connection;
}
private static String extractResponseString(URLConnection connection) throws IOException {
/* Handle input. */
HttpURLConnection http = (HttpURLConnection)connection;
int status = http.getResponseCode();
String charset = getCharset(connection.getHeaderField("Content-Type"));
if (status==200) {
return readResponseBody(http, charset);
} else {
return readErrorResponseBody(http, status, charset);
}
}
private static String readErrorResponseBody(HttpURLConnection http, int status, String charset) {
InputStream errorStream = http.getErrorStream();
if ( errorStream!=null ) {
String error = charset== null ? read( errorStream ) :
read( errorStream, charset );
throw new RuntimeException("STATUS CODE =" + status + "\n\n" + error);
} else {
throw new RuntimeException("STATUS CODE =" + status);
}
}
private static String readResponseBody(HttpURLConnection http, String charset) throws IOException {
if (charset != null) {
return read(http.getInputStream(), charset);
} else {
return read(http.getInputStream());
}
}
private static String getCharset(String contentType) {
if (contentType==null) {
return null;
}
String charset = null;
for (String param : contentType.replace(" ", "").split(";")) {
if (param.startsWith("charset=")) {
charset = param.split("=", 2)[1];
break;
}
}
charset = charset == null ? IO.CHARSET : charset;
return charset;
}
嗯，你明白了。。。。
以下是测试：
static class MyHandler implements HttpHandler {
public void handle(HttpExchange t) throws IOException {
InputStream requestBody = t.getRequestBody();
String body = IO.read(requestBody);
Headers requestHeaders = t.getRequestHeaders();
body = body + "\n" + copy(requestHeaders).toString();
t.sendResponseHeaders(200, body.length());
OutputStream os = t.getResponseBody();
os.write(body.getBytes());
os.close();
}
}
@Test
public void testHappy() throws Exception {
HttpServer server = HttpServer.create(new InetSocketAddress(9212), 0);
server.createContext("/test", new MyHandler());
server.setExecutor(null); // creates a default executor
server.start();
Thread.sleep(10);
Map<String,String> headers = map("foo", "bar", "fun", "sun");
String response = HTTP.postBodyWithContentType("http://localhost:9212/test", headers, "text/plain", "hi mom");
System.out.println(response);
assertTrue(response.contains("hi mom"));
assertTrue(response.contains("Fun=[sun], Foo=[bar]"));
response = HTTP.postBodyWithCharset("http://localhost:9212/test", headers, "text/plain", "UTF-8", "hi mom");
System.out.println(response);
assertTrue(response.contains("hi mom"));
assertTrue(response.contains("Fun=[sun], Foo=[bar]"));
response = HTTP.postBodyWithHeaders("http://localhost:9212/test", headers, "hi mom");
System.out.println(response);
assertTrue(response.contains("hi mom"));
assertTrue(response.contains("Fun=[sun], Foo=[bar]"));
response = HTTP.get("http://localhost:9212/test");
System.out.println(response);
response = HTTP.getWithHeaders("http://localhost:9212/test", headers);
System.out.println(response);
assertTrue(response.contains("Fun=[sun], Foo=[bar]"));
response = HTTP.getWithContentType("http://localhost:9212/test", headers, "text/plain");
System.out.println(response);
assertTrue(response.contains("Fun=[sun], Foo=[bar]"));
response = HTTP.getWithCharSet("http://localhost:9212/test", headers, "text/plain", "UTF-8");
System.out.println(response);
assertTrue(response.contains("Fun=[sun], Foo=[bar]"));
Thread.sleep(10);
server.stop(0);
}
@Test
public void testPostBody() throws Exception {
HttpServer server = HttpServer.create(new InetSocketAddress(9220), 0);
server.createContext("/test", new MyHandler());
server.setExecutor(null); // creates a default executor
server.start();
Thread.sleep(10);
Map<String,String> headers = map("foo", "bar", "fun", "sun");
String response = HTTP.postBody("http://localhost:9220/test", "hi mom");
assertTrue(response.contains("hi mom"));
Thread.sleep(10);
server.stop(0);
}
@Test(expected = RuntimeException.class)
public void testSad() throws Exception {
HttpServer server = HttpServer.create(new InetSocketAddress(9213), 0);
server.createContext("/test", new MyHandler());
server.setExecutor(null); // creates a default executor
server.start();
Thread.sleep(10);
Map<String,String> headers = map("foo", "bar", "fun", "sun");
String response = HTTP.postBodyWithContentType("http://localhost:9213/foo", headers, "text/plain", "hi mom");
System.out.println(response);
assertTrue(response.contains("hi mom"));
assertTrue(response.contains("Fun=[sun], Foo=[bar]"));
Thread.sleep(10);
server.stop(0);
}
您可以在此处找到其余内容：
https://github.com/RichardHightower/boon
我的目标是以一种更简单的方式提供人们想要做的常见事情。。。。
受Stack Overflow的这些问题和其他问题的启发，我创建了一个最小的开源基本http客户端，它体现了这里找到的大多数技术。
googlehttpjava客户端也是一个很好的开源资源。
在使用HTTP时，引用HttpURLConnection而不是基类URLConnection几乎总是更有用（因为URLConnection是一个抽象类，当您在HTTP URL上请求URLConnection.openConnection（）时，无论如何都会返回）。
然后，您可以不依赖URLConnection#setDoOutput（true）将请求方法隐式设置为POST，而是使用httpURLConnection.setRequestMethod（“POST”），有些人可能会觉得这更自然（这也允许您指定其他请求方法，如PUT、DELETE…）。
它还提供了有用的HTTP常量，因此您可以执行以下操作：
int responseCode = httpURLConnection.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) {
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