1 <!-- 2 Copyright (c) 1998, 2012, Oracle and/or its affiliates. All rights reserved. 3 DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 5 This code is free software; you can redistribute it and/or modify it 6 under the terms of the GNU General Public License version 2 only, as 7 published by the Free Software Foundation. Oracle designates this 8 particular file as subject to the "Classpath" exception as provided 9 by Oracle in the LICENSE file that accompanied this code. 10 11 This code is distributed in the hope that it will be useful, but WITHOUT 12 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 version 2 for more details (a copy is included in the LICENSE file that 15 accompanied this code). 16 17 You should have received a copy of the GNU General Public License version 18 2 along with this work; if not, write to the Free Software Foundation, 19 Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 21 Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 or visit www.oracle.com if you need additional information or have any 23 questions. 24 --> 25 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> 26 <HTML> 27 <HEAD> 28 <META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=iso-8859-1"> 29 <TITLE>Networking Properties</TITLE> 30 </HEAD> 31 <BODY LANG="en-US" DIR="LTR"> 32 <H1 ALIGN=CENTER>Networking Properties</H1> 33 <P ALIGN=LEFT>There are a few standard system properties used to 34 alter the mechanisms and behavior of the various classes of the 35 java.net package. Some are checked only once at startup of the VM, 36 and therefore are best set using the -D option of the java command, 37 while others have a more dynamic nature and can also be changed using 38 the <a href="../../lang/System.html#setProperty(java.lang.String,%20java.lang.String)">System.setProperty()</a> API. The purpose of this document is to list 39 and detail all of these properties.</P> 40 <P>If there is no special note, a property value is checked every time it is used.</P> 41 <a name="Ipv4IPv6"></a> 42 <H2>IPv4 / IPv6</H2> 43 <UL> 44 <LI><P><B>java.net.preferIPv4Stack</B> (default: false)<BR> 45 If IPv6 is available on the operating system the 46 underlying native socket will be, by default, an IPv6 socket which 47 lets applications connect to, and accept connections from, both 48 IPv4 and IPv6 hosts. However, in the case an application would 49 rather use IPv4 only sockets, then this property can be set to <B>true</B>. 50 The implication is that it will not be possible for the application 51 to communicate with IPv6 only hosts.</P> 52 <LI><P><B>java.net.preferIPv6Addresses</B> (default: false)<BR> 53 When dealing with a host which has both IPv4 54 and IPv6 addresses, and if IPv6 is available on the operating 55 system, the default behavior is to prefer using IPv4 addresses over 56 IPv6 ones. This is to ensure backward compatibility, for example 57 applications that depend on the representation of an IPv4 address 58 (e.g. 192.168.1.1). This property can be set to <B>true</B> to 59 change that preference and use IPv6 addresses over IPv4 ones where 60 possible.</P> 61 </UL> 62 <P>Both of these properties are checked only once, at startup.</P> 63 <a name="Proxies"></a> 64 <H2>Proxies</H2> 65 <P>A proxy server allows indirect connection to network services and 66 is used mainly for security (to get through firewalls) and 67 performance reasons (proxies often do provide caching mechanisms). 68 The following properties allow for configuration of the various type 69 of proxies.</P> 70 <UL> 71 <LI><P>HTTP</P> 72 <P>The following proxy settings are used by the HTTP protocol handler.</P> 73 <UL> 74 <LI><P><B>http.proxyHost</B> (default: <none>)<BR> 75 The hostname, or address, of the proxy server 76 </P> 77 <LI><P><B>http.proxyPort</B> (default: 80)<BR> 78 The port number of the proxy server.</P> 79 <LI><P><B>http.nonProxyHosts</B> (default: localhost|127.*|[::1])<BR> 80 Indicates the hosts that should be accessed without going 81 through the proxy. Typically this defines internal hosts. 82 The value of this property is a list of hosts, 83 separated by the '|' character. In addition the wildcard 84 character '*' can be used for pattern matching. For example 85 <code>-Dhttp.nonProxyHosts=”*.foo.com|localhost”</code> 86 will indicate that every hosts in the foo.com domain and the 87 localhost should be accessed directly even if a proxy server is 88 specified.</P> 89 <P>The default value excludes all common variations of the loopback address.</P> 90 </UL> 91 <LI><P>HTTPS<BR>This is HTTP over SSL, a secure version of HTTP 92 mainly used when confidentiality (like on payment sites) is needed.</P> 93 <P>The following proxy settings are used by the HTTPS protocol handler.</P> 94 <UL> 95 <LI><P><B>https.proxyHost</B>(default: <none>)<BR> 96 The hostname, or address, of the proxy server 97 </P> 98 <LI><P><B>https.proxyPort</B> (default: 443)<BR> 99 The port number of the proxy server.</P> 100 <P>The HTTPS protocol handler will use the same nonProxyHosts 101 property as the HTTP protocol.</P> 102 </UL> 103 <LI><P>FTP</P> 104 <P>The following proxy settings are used by the FTP protocol handler.</P> 105 <UL> 106 <LI><P><B>ftp.proxyHost</B>(default: <none>)<BR> 107 The hostname, or address, of the proxy server 108 </P> 109 <LI><P><B>ftp.proxyPort</B> (default: 80)<BR> 110 The port number of the proxy server.</P> 111 <LI><P><B>ftp.nonProxyHosts</B> (default: localhost|127.*|[::1])<BR> 112 Indicates the hosts that should be accessed without going 113 through the proxy. Typically this defines internal hosts. 114 The value of this property is a list of hosts, separated by 115 the '|' character. In addition the wildcard character 116 '*' can be used for pattern matching. For example 117 <code>-Dhttp.nonProxyHosts=”*.foo.com|localhost”</code> 118 will indicate that every hosts in the foo.com domain and the 119 localhost should be accessed directly even if a proxy server is 120 specified.</P> 121 <P>The default value excludes all common variations of the loopback address.</P> 122 </UL> 123 <LI><P>SOCKS<BR>This is another type of proxy. It allows for lower 124 level type of tunneling since it works at the TCP level. In effect, 125 in the Java(tm) platform setting a SOCKS proxy server will result in 126 all TCP connections to go through that proxy, unless other proxies 127 are specified. If SOCKS is supported by a Java SE implementation, the 128 following properties will be used:</P> 129 <UL> 130 <LI><P><B>socksProxyHost</B> (default: <none>)<BR> 131 The hostname, or address, of the proxy server.</P> 132 <LI><P><B>socksProxyPort</B> (default: 1080)<BR> 133 The port number of the proxy server.</P> 134 <LI><P><B>socksProxyVersion</B> (default: 5)<BR> 135 The version of the SOCKS protocol supported by the server. The 136 default is <code>5</code> indicating SOCKS V5, alternatively 137 <code>4</code> can be specified for SOCKS V4. Setting the property 138 to values other than these leads to unspecified behavior.</P> 139 <LI><P><B>java.net.socks.username</B> (default: <none>)<BR> 140 Username to use if the SOCKSv5 server asks for authentication 141 and no java.net.Authenticator instance was found.</P> 142 <LI><P><B>java.net.socks.password</B> (default: <none>)<BR> 143 Password to use if the SOCKSv5 server asks for authentication 144 and no java.net.Authenticator instance was found.</P> 145 <P>Note that if no authentication is provided with either the above 146 properties or an Authenticator, and the proxy requires one, then 147 the <B>user.name</B> property will be used with no password.</P> 148 </UL> 149 <LI><P><B>java.net.useSystemProxies</B> (default: false)<BR> 150 On recent Windows systems and on Gnome 2.x systems it is possible to 151 tell the java.net stack, setting this property to <B>true</B>, to use 152 the system proxy settings (both these systems let you set proxies 153 globally through their user interface). Note that this property is 154 checked only once at startup.</P> 155 </UL> 156 <a name="MiscHTTP"></a> 157 <H2>Misc HTTP properties</H2> 158 <UL> 159 <LI><P><B>http.agent</B> (default: “Java/<version>”)<BR> 160 Defines the string sent in the User-Agent request header in http 161 requests. Note that the string “Java/<version>” will 162 be appended to the one provided in the property (e.g. if 163 -Dhttp.agent=”foobar” is used, the User-Agent header will 164 contain “foobar Java/1.5.0” if the version of the VM is 165 1.5.0). This property is checked only once at startup.</P> 166 <LI><P><B>http.keepalive</B> (default: true)<BR> 167 Indicates if persistent connections should be supported. They improve 168 performance by allowing the underlying socket connection to be reused 169 for multiple http requests. If this is set to true then persistent 170 connections will be requested with HTTP 1.1 servers.</P> 171 <LI><P><B>http.maxConnections</B> (default: 5)<BR> 172 If HTTP keepalive is enabled (see above) this value determines the 173 maximum number of idle connections that will be simultaneously kept 174 alive, per destination.</P> 175 <LI><P><B>http.maxRedirects</B> (default: 20)<BR> 176 This integer value determines the maximum number, for a given request, 177 of HTTP redirects that will be automatically followed by the 178 protocol handler.</P> 179 <LI><P><B>http.auth.digest.validateServer</B> (default: false)</P> 180 <LI><P><B>http.auth.digest.validateProxy</B> (default: false)</P> 181 <LI><P><B>http.auth.digest.cnonceRepeat</B> (default: 5)</P> 182 <P>These 3 properties modify the behavior of the HTTP digest 183 authentication mechanism. Digest authentication provides a limited 184 ability for the server to authenticate itself to the client (i.e. 185 By proving it knows the user's password). However not all HTTP 186 servers support this capability and by default it is turned off. The 187 first two properties can be set to true to enforce this check for 188 authentication with either an origin or proxy server, respectively.</P> 189 <P>It is usually not necessary to change the third property. It 190 determines how many times a cnonce value is re-used. This can be 191 useful when the MD5-sess algorithm is being used. Increasing this 192 value reduces the computational overhead on both client and server 193 by reducing the amount of material that has to be hashed for each 194 HTTP request.</P> 195 <LI><P><B>http.auth.ntlm.domain</B> (default: <none>)<BR> 196 NTLM is another authentication scheme. It uses the 197 java.net.Authenticator class to acquire usernames and passwords when 198 they are needed. However NTLM also needs the NT domain name. There are 199 3 options for specifying that domain:</P> 200 <OL> 201 <LI><P>Do not specify it. In some environments the domain is 202 actually not required and the application does not have to specify 203 it.</P> 204 <LI><P>The domain name can be encoded within the username by 205 prefixing the domain name, followed by a back-slash '\' before the 206 username. With this method existing applications that use the 207 authenticator class do not need to be modified, as long as users 208 are made aware that this notation must be used.</P> 209 <LI><P>If a domain name is not specified as in method 2) and these 210 property is defined, then its value will be used a the domain 211 name.</P> 212 </OL> 213 </UL> 214 <P>All these properties are checked only once at startup.</P> 215 <a name="AddressCache"></a> 216 <H2>Address Cache</H2> 217 <P>The java.net package, when doing name resolution, uses an address 218 cache for both security and performance reasons. Any address 219 resolution attempt, be it forward (name to IP address) or reverse (IP 220 address to name), will have its result cached, whether it was 221 successful or not, so that subsequent identical requests will not 222 have to access the naming service. These properties allow for some 223 tuning on how the cache is operating.</P> 224 <UL> 225 <LI><P><B>networkaddress.cache.ttl</B> (default: see below)<BR> 226 Value is an integer corresponding to the number of seconds successful 227 name lookups will be kept in the cache. A value of -1, or any other 228 negative value for that matter, indicates a “cache forever” 229 policy, while a value of 0 (zero) means no caching. The default value 230 is -1 (forever) if a security manager is installed, and implementation 231 specific when no security manager is installed.</P> 232 <LI><P><B>networkaddress.cache.negative.ttl</B> (default: 10)<BR> 233 Value is an integer corresponding to the number of seconds an 234 unsuccessful name lookup will be kept in the cache. A value of -1, 235 or any negative value, means “cache forever”, while a 236 value of 0 (zero) means no caching.</P> 237 </UL> 238 <P>Since these 2 properties are part of the security policy, they are 239 not set by either the -D option or the System.setProperty() API, 240 instead they are set as security properties.</P> 241 </BODY> 242 </HTML>