你可以通过编程的方式设置这些标志:

if (needsProxy()) {
    System.setProperty("http.proxyHost",getProxyHost());
    System.setProperty("http.proxyPort",getProxyPort());
} else {
    System.setProperty("http.proxyHost","");
    System.setProperty("http.proxyPort","");
}

只要从方法needsProxy()， getProxyHost()和getProxyPort()中返回正确的值，您就可以随时调用此代码片段。

可以将代理服务器的一些属性设置为jvm参数

-Dhttp。proxyPort=8080, proxyHost，等等。

但是如果你需要通过一个认证代理，你需要一个像下面这样的验证器:

ProxyAuthenticator.java

import java.net.*;
import java.io.*;

public class ProxyAuthenticator extends Authenticator {

    private String userName, password;

    protected PasswordAuthentication getPasswordAuthentication() {
        return new PasswordAuthentication(userName, password.toCharArray());
    }

    public ProxyAuthenticator(String userName, String password) {
        this.userName = userName;
        this.password = password;
    }
}

Example.java

    import java.net.Authenticator;
    import ProxyAuthenticator;

public class Example {

    public static void main(String[] args) {
        String username = System.getProperty("proxy.authentication.username");
        String password = System.getProperty("proxy.authentication.password");

                if (username != null && !username.equals("")) {
            Authenticator.setDefault(new ProxyAuthenticator(username, password));
        }

                // here your JVM will be authenticated

    }
}

根据这个回复: http://mail-archives.apache.org/mod_mbox/jakarta-jmeter-user/200208.mbox/%3C494FD350388AD511A9DD00025530F33102F1DC2C@MMSX006%3E

这是一个对我有用的完整示例-注意，对于HTTPS有单独的属性(根据https://docs.oracle.com/javase/8/docs/technotes/guides/net/proxies.html)。

下面的代码向https://api.myip.com API发送请求并打印响应。

public static void main(String[] args) throws IOException {
    System.setProperty("java.net.useSystemProxies", "true");
    final String proxyUser = "proxy-user";
    final String proxyPass = "password123";
    final String host = "some.proxy.io";
    final Integer port = 50201;

    // http
    System.setProperty("http.proxyHost",host);
    System.setProperty("http.proxyPort", String.valueOf(port));
    System.setProperty("http.proxyUser", proxyUser);
    System.setProperty("http.proxyPassword", proxyPass);

    // https
    System.setProperty("https.proxyHost",host);
    System.setProperty("https.proxyPort", String.valueOf(port));
    System.setProperty("https.proxyUser", proxyUser);
    System.setProperty("https.proxyPassword", proxyPass);

    System.setProperty("jdk.http.auth.tunneling.disabledSchemes", "");
    System.setProperty("jdk.https.auth.tunneling.disabledSchemes", "");

    Authenticator.setDefault(new Authenticator() {
                @Override
                public PasswordAuthentication getPasswordAuthentication() {
                    return new PasswordAuthentication(proxyUser, proxyPass.toCharArray());
                }
        }
    );

    // create and send a https request to myip.com API
    URL url = new URL("https://api.myip.com");
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
    connection.setRequestMethod("GET");
    int status = connection.getResponseCode();
    
    // read the response
    BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
    String responseLine;
    StringBuffer responseContent = new StringBuffer();
    while ((responseLine = in.readLine()) != null) 
        responseContent.append(responseLine);
    
    in.close();
    connection.disconnect();
    
    // print the response
    System.out.println(status);
    System.out.println(responseContent);
}

我也在防火墙后面，这对我有用!!

System.setProperty("http.proxyHost", "proxy host addr");
System.setProperty("http.proxyPort", "808");
Authenticator.setDefault(new Authenticator() {
    protected PasswordAuthentication getPasswordAuthentication() {

        return new PasswordAuthentication("domain\\user","password".toCharArray());
    }
});

URL url = new URL("http://www.google.com/");
URLConnection con = url.openConnection();

BufferedReader in = new BufferedReader(new InputStreamReader(
                    con.getInputStream()));

// Read it ...
String inputLine;
while ((inputLine = in.readLine()) != null)
    System.out.println(inputLine);

in.close();

读取一个XML文件，并需要下载它的模式

如果您依赖于通过internet检索模式或dtd，那么您正在构建一个缓慢、频繁且脆弱的应用程序。当托管文件的远程服务器发生计划内或计划外停机时，会发生什么?你的应用程序崩溃了。这样可以吗?

看到http://xml.apache.org/commons/components/resolver/resolver-article.html s.catalog.files

模式和类似的URL最好被认为是唯一标识符。而不是远程访问文件的请求。在“XML目录”上做一些谷歌搜索。XML目录允许您在本地托管这些资源，从而解决了慢、多和脆弱的问题。

它基本上是远程内容的永久缓存副本。这是可以的，因为远程内容永远不会改变。如果有更新，也会是另一个网址。使得在互联网上实际检索资源变得特别愚蠢。

这是一个小更新，但是从Java 7开始，现在可以通过编程方式创建代理连接，而不是通过系统属性。这可能是有用的，如果:

代理需要在程序运行时动态旋转 需要使用多个并行代理 或者只是让你的代码更干净:)

这是groovy中一个人为的例子:

// proxy configuration read from file resource under "proxyFileName"
String proxyFileName = "proxy.txt"
String proxyPort = "1234"
String url = "http://www.promised.land"
File testProxyFile = new File(proxyFileName)
URLConnection connection

if (!testProxyFile.exists()) {

    logger.debug "proxyFileName doesn't exist.  Bypassing connection via proxy."
    connection = url.toURL().openConnection()

} else {
    String proxyAddress = testProxyFile.text
    connection = url.toURL().openConnection(new Proxy(Proxy.Type.HTTP, new InetSocketAddress(proxyAddress, proxyPort)))
}

try {
    connection.connect()
}
catch (Exception e) {
    logger.error e.printStackTrace()
}

全部参考: http://docs.oracle.com/javase/7/docs/technotes/guides/net/proxies.html