During development, we usually need use fiddler to monitor/debug request and response. This article introduce how to set proxy in code or in command line to use fiddler as a proxy.

Set Proxy When Use HttpURLConnection
If we are using Java HttpURLConnection, we can set the following system environment in test code:
System.setProperty(“http.proxyHost”, “localhost”);
System.setProperty(“http.proxyPort”, “8888”);
or set them as JVM parameters in command line:
-Dhttp.proxyHost=localhost -Dhttp.proxyPort=8888

Set Proxy in the Code When Use Apache HTTP Client 4.x
HttpHost proxy = new HttpHost(“”, 8888, “http”);
httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy);
Set Proxy When Use Apache HTTP Client 3.x
HttpClient client = new HttpClient();
client.getHostConfiguration().setProxy(“”, 8888);

Set Proxy in Command Line When Use Apache HTTP Client 4.2 or Newer
If we are using 4.2 or newer Apache HTTP Client, we can use SystemDefaultHttpClient, which honors JSSE and networking system properties, such as http.proxyHost, http.proxyPort

How this is implemented in SystemDefaultHttpClient
SystemDefaultHttpClient uses ProxySelector.getDefault(), which uses DefaultProxySelector. DefaultProxySelector uses NetProperties to read system properties.

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Set Proxy in Command Line When Use Apache HTTP Client 3.x
If we are using Apache HTTP Client 3.x, we can read system property: proxyHost and proxyPort. If they are not empty, set proxy.

String proxyHost = System.getProperty("http.proxyHost");
String proxyPort = System.getProperty("http.proxyPort");

if (StringUtils.isNotBlank(proxyHost)
  && StringUtils.isNotBlank(proxyPort)) {

We use similar logic to set proxy when use older Apache HTTP Client 4.x.

Java Networking and Proxies

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