Proxy Configuration

This page discussing proxy issues on command-line Apache Ant. Consult your IDE documentation for IDE-specific information upon proxy setup.

All tasks and threads running in Ant's JVM share the same HTTP/FTP/Socks proxy configuration.

When any task tries to retrieve content from an HTTP page, including the <get> task, any automated URL retrieval in an XML/XSL task, or any third-party task that uses the classes, the proxy settings may make the difference between success and failure.

Anyone authoring a build file behind a blocking firewall will immediately appreciate the problems and may want to write a build file to deal with the problem, but users of third party build build files may find that the build file itself does not work behind the firewall.

This is a long standing problem with Java and Ant. The only way to fix it is to explicitly configure Ant with the proxy settings, either by passing down the proxy details as JVM properties, or to tell Ant on a Java1.5+ system to have the JVM work it out for itself.

Java1.5+ proxy support (new for Ant1.7)

When Ant starts up, if the -autoproxy command is supplied, Ant sets the system property. This tells a Java1.5+ JVM to use the current set of property settings of the host environment. Other JVMs, such as the Kaffe and Apache Harmony runtimes, may also use this property in future. It is ignored on the Java1.4 and earlier runtimes.

This property maybe enough to give command-line Ant builds network access, although in practise the results are inconsistent.

It is has also been reported a breaking the IBM Java 5 JRE on AIX, and does not always work on Linux (presumably due to missing gconf settings) Other odd things can go wrong, like Oracle JDBC drivers or pure Java SVN clients.

To make the -autoproxy option the default, add it to the environment variable ANT_ARGS, which contains a list of arguments to pass to Ant on every command line run.

How Autoproxy works

The is checked only once, at startup time, the other checks (registry, gconf, system properties) are done dynamically whenever needed (socket connection, URL connection etc..).


The JVM goes straight to the registry, bypassing WinInet, as it is not present/consistent on all supported Windows platforms (it is part of IE, really). Java 7 may use the Windows APIs on the platforms when it is present.


The JVM uses the gconf library to look at specific entries. The GConf-2 settings used are:

 - /system/http_proxy/use_http_proxy            boolean
 - /system/http_proxy/use_authentication        boolean
 - /system/http_proxy/host                      string
 - /system/http_proxy/authentication_user       string
 - /system/http_proxy/authentication_password   string
 - /system/http_proxy/port                      int
 - /system/proxy/socks_host                     string
 - /system/proxy/mode                           string
 - /system/proxy/ftp_host                       string
 - /system/proxy/secure_host                    string
 - /system/proxy/socks_port                     int
 - /system/proxy/ftp_port                       int
 - /system/proxy/secure_port                    int
 - /system/proxy/no_proxy_for                   list
 - /system/proxy/gopher_host                    string
 - /system/proxy/gopher_port                    int

If you are using KDE or another GUI than Gnome, you can still use the gconf-editor tool to add these entries.

Manual JVM options

Any JVM can have its proxy options explicitly configured by passing the appropriate -D system property options to the runtime. Ant can be configured through all its shell scripts via the ANT_OPTS environment variable, which is a list of options to supply to Ant's JVM:

For bash:

    export ANT_OPTS="-Dhttp.proxyHost=proxy -Dhttp.proxyPort=8080"
For csh/tcsh:
    setenv ANT_OPTS "-Dhttp.proxyHost=proxy -Dhttp.proxyPort=8080"

If you insert this line into the Ant shell script itself, it gets picked up by all continuous integration tools running on the system that call Ant via the command line.

For Windows, set the ANT_OPTS environment variable in the appropriate "My Computer" properties dialog box (winXP), "Computer" properties (Vista)

This mechanism works across Java versions, is cross-platform and reliable. Once set, all build files run via the command line will automatically have their proxy setup correctly, without needing any build file changes. It also apparently overrides Ant's automatic proxy settings options.

It is limited in the following ways:

  1. Does not work under IDEs. These need their own proxy settings changed
  2. Not dynamic enough to deal with laptop configuration changes.

SetProxy Task

The setproxy task can be used to explicitly set a proxy in a build file. This manipulates the many proxy configuration properties of a JVM, and controls the proxy settings for all network operations in the same JVM from that moment.

If you have a build file that is only to be used in-house, behind a firewall, on an older JVM, and you cannot change Ant's JVM proxy settings, then this is your best option. It is ugly and brittle, because the build file now contains system configuration information. It is also hard to get this right across the many possible proxy options of different users (none, HTTP, SOCKS).

Note that proxy configurations set with this task will probably override any set by other mechanisms. It can also be used with fancy tricks to only set a proxy if the proxy is considered reachable:

  <target name="probe-proxy" depends="init">
    <condition property="proxy.enabled">
        <isset property=""/>
        <isreachable host="${}"/>

  <target name="proxy" depends="probe-proxy" if="proxy.enabled">
    <property name="proxy.port" value="80"/>
    <property name="proxy.user" value=""/>
    <property name="proxy.pass" value=""/>
    <setproxy proxyhost="${}" proxyport="${proxy.port}"
      proxyuser="${proxy.user}" proxypassword="${proxy.pass}"/>

Custom ProxySelector implementations

As Java lets developers write their own ProxySelector implementations, it is theoretically possible for someone to write their own proxy selector class that uses different policies to determine proxy settings. There is no explicit support for this in Ant, and it has not, to the team's knowledge, been attempted.

This could be the most flexible of solutions, as one could easily imagine an Ant-specific proxy selector that was driven off ant properties, rather than system properties. Developers could set proxy options in their custom files, and have this propagate.

One issue here is with concurrency: the default proxy selector is per-JVM, not per-thread, and so the proxy settings will apply to all sockets opened on all threads; we also have the problem of how to propagate options from one build to the JVM-wide selector.

Configuring the Proxy settings of Java programs under Ant

Any program that is executed with <java> without setting fork="true" will pick up the Ant's settings. If you need different values, set fork="false" and provide the values in <sysproperty> elements.

If you wish to have a forked process pick up the Ant's settings, use the <syspropertyset> element to propagate the normal proxy settings. The following propertyset is a datatype which can be referenced in a <java> task to pass down the current values.

<propertyset id="">
  <propertyref prefix=""/>
  <propertyref prefix="http."/>
  <propertyref prefix="https."/>
  <propertyref prefix="ftp."/>
  <propertyref prefix="socksProxy"/>

Summary and conclusions

There are four ways to set up proxies in Ant.

  1. With Ant1.7 and Java 1.5+ using the -autoproxy parameter.
  2. Via JVM system properties -set these in the ANT_ARGS environment variable.
  3. Via the <setproxy> task.
  4. Custom ProxySelector implementations

Proxy settings are automatically shared with Java programs started under Ant that are not forked; to pass proxy settings down to subsidiary programs, use a propertyset.

Over time, we expect the Java 5+ proxy features to stabilize, and for Java code to adapt to them. However, given the fact that it currently does break some builds, it will be some time before Ant enables the automatic proxy feature by default. Until then, you have to enable the -autoproxy option or use one of the alternate mechanisms to configure the JVM.

Further reading