检索 Java net.properties 文件中定义的默认值 [英] retrieving default values defined in Java net.properties file

问题描述

如果我了解 Java 网络和代理 正确，jre/lib/net.properties 文件包含在运行时填充到系统属性中的默认值.我的 net.properties 文件包含以下内容:

If I understand Java Networking and Proxies correctly, the jre/lib/net.properties file contains default values that are populated into the system properties at runtime. My net.properties file contains the following, among other things:

http.nonProxyHosts=localhost|127.*|[::1]

但是当我在 Eclipse 4.5 中运行我的 Java 应用程序时，System.getProperty("http.nonProxyHosts") 返回 null.我没有在我的应用程序中的任何地方定义或覆盖这个值.

But when I run my Java application inside Eclipse 4.5, System.getProperty("http.nonProxyHosts") returns null. I have not defined or overridden this value anywhere within my application.

如何在运行时检索 jre/lib/net.properties 中定义的 http.nonProxyHosts 的值?

How am I able to retrieve the value of http.nonProxyHosts defined in jre/lib/net.properties at runtime?

推荐答案

结论总结

1. 文件 ${java.home}/lib/net.properties 未加载到 系统属性 (System::getProperties).
2. 通过 System.setProperty 手动设置代理，或在命令行设置，例如使用 -Dhttp.proxyHost=proxy 语法，将覆盖定义的属性，还有任何 java.net.useSystemProxies 设置，即使设置为 true.
3. 您可以通过使用 Properties::load.确切位置在 Java 主目录中，可以使用 java.home 系统属性，位于 lib 子目录中.
4. 在 Windows 桌面上，当与 java.net.useSystemProxies=true 结合使用时，您可以从控制面板的Internet 属性"下设置使用的代理.在这些设置中，您需要点击LAN 设置"按钮.
5. 小程序具有额外的设置级别，请参阅代理设置在 Java 文档中.

1. The file ${java.home}/lib/net.properties does not get loaded into the System Properties (System::getProperties).
2. Setting the proxy manually either through System.setProperty, or setting at the command line, for example using -Dhttp.proxyHost=proxy syntax, will override the the defined property, but also any java.net.useSystemProxies setting even if set to true.
3. You can access the net.properties file by loading it manually as properties using Properties::load. The exact location is in the Java Home directory, which can be retrieved using the java.home System Property, within the lib subdirectory.
4. On a windows desktop, when used in combination with java.net.useSystemProxies=true, you set the proxy used from the control panel, under 'Internet Properties'. From those settings you will need to click on the 'LAN settings' button.
5. An applet has an additional level of settings, see Proxy Setup in the Java documentation.

研究

我已经在我的环境中复制了你的例子，实际上使用了 netBeans，这个简单的例子是:

Research

I have replicated your example in my environment, using netBeans actually, with this simple example:

public class Play {
  public static void main(String args[]) { 
    System.out.println(System.getProperty("java.home"));
    System.out.println(System.getProperty("http.nonProxyHosts"));
    System.out.println(System.getProperty("java.net.useSystemProxies"));
 }
}

我打印了 java.home 系统属性以确保我正在编辑正确的 jre/lib/net.properties.

I print the java.home system property to make sure I am editing the correct jre/lib/net.properties.

但是两个属性 http.nonProxyHosts 和 java.net.useSystemProxies 打印为空，而我可以清楚地看到这两个值都在 net 中设置.properties 文件:

however the two properties http.nonProxyHosts and java.net.useSystemProxies print as null, while I can clearly see that both values are set in the net.properties file:

java.net.useSystemProxies=false
http.nonProxyHosts=localhost|127.*|[::1]

实际上文档有点不清楚，但似乎可以通过以下几种方式之一完成代理配置:

Actually the documentation is a little unclear, but it seems that proxy configuration can be done in one of several ways:

1. jre/lib/net.properties 作为默认值
2. 当 java.net.useSystemProxies 设置为 true 时，从您系统的互联网设置(控制面板等).
3. 来自 Java 配置，在您的 Java 控制面板中设置，当作为小程序运行时，可能从您的浏览器设置继承.
4. System.properties

1. jre/lib/net.properties as the default
2. From your System's internet settings (Control Panel etc) when java.net.useSystemProxies is set to true.
3. From the Java Configuration, as set in your Java Control panel, and when ran as an Applet, and potentially inherited from your browser settings.
4. System.properties

在我看来，这是 java.net api 的一个自定义功能，只有在未明确设置系统属性的情况下才会读取 net.properties.我怀疑 not 是否意味着 net.properties 文件用于设置系统属性，但只能由 java.net api 自己读取.

It appears to me that this is a cusom feature of the java.net api's, and will read the net.properties only in case the system properties are not set explicitly. I suspect that does not mean that the net.properties file is used to set system properties, but are only read by the java.net api's themselves.

还要注意默认安装的 net.properties 文件中的这段文字:

Note also this text within the default installed net.properties file:

此文件可能包含网络系统的默认值特性.这些值仅在系统属性为未在命令行中指定或以编程方式设置.

This file may contain default values for the networking system properties. These values are only used when the system properties are not specified on the command line or set programatically.

它只是说这些值将被使用，没有具体设置系统属性本身.

It only says that these values will be used, nothing specific about setting the system properties themselves.

[更新]

通过一个小例子，我能够证明这一点

With a small example, I was able to prove that out

import java.net.Proxy;
import java.net.ProxySelector;
import java.net.URI;
import java.util.List;

public class Play {
  public static void main(String args[]) { 
    System.out.println(System.getProperty("java.home"));
    System.out.println(System.getProperty("http.proxyHost"));
    ProxySelector ps = ProxySelector.getDefault();
    List<Proxy> proxies = ps.select(URI.create("http://www.yahoo.com"));
    System.out.println("HTTP Proxies");
    for (Proxy p:proxies) {
      System.out.append(p.toString()).append("
");
    }
 }
}

您可以看到 http.proxyHost 打印为 null，而使用默认的 net.properties，"http://www.yahoo.com" 打印为 DIRECT.DIRECT 表示没有代理.这是因为在 net.properties 文件中，http.proxyHost` 未定义.

You can see that the http.proxyHost prints as null, while with the default net.properties, the proxy for "http://www.yahoo.com" prints as DIRECT. DIRECT means no proxy. This is because in the net.properties file,http.proxyHost` is undefined.

现在我修改 net.properties 文件如下(取消注释并修改现有条目):

Now I modify the net.properties file as follows (un-commenting and modifying the existing entry):

http.proxyHost=this.is.a.test.net

现在，当我运行相同的代码时，我得到以下输出:

Now when I run the same code, I get following output:

C:Program FilesJavajdk1.8.0_20jre
null
HTTP Proxies
HTTP @ this.is.a.test.net:80

系统属性仍然为空，但是 net.properties 文件中的相同设置确实生效了.

The System Property is still null, however the same setting from the net.properties file did take effect.

其他一些观察:

1. 当如下明确设置系统属性时:System.setProperty("http.proxyHost", "other.net"); 就在执行 ProxySelector::select 之前>，将覆盖 net.properties 中的值.
2. 使用系统属性覆盖将仅影响完全相同的系统属性.也就是说，如果您只覆盖 http.proxyHost，如果在 net.properties 中设置，它仍然会继承 http.proxyPort.
3. 如果在任何地方，无论是在 net.properties 文件中，还是通过在代码中显式设置系统属性，我都会显式设置 http.proxyHost，这将始终覆盖即使 java.net.useSystemProxies 设置为 true，系统默认也是如此.java.net.useSystemProxies=true 仅在未明确设置代理时有效，否则将被忽略(我已经测试并验证了这一点).

1. When setting the system property explicitly as follows: System.setProperty("http.proxyHost", "other.net"); right before doing the ProxySelector::select, will override the value in net.properties.
2. Overriding using the system properties will only affect the exact same system property. That is, if you only override http.proxyHost, it will still inherit http.proxyPort if set in net.properties.
3. If anywhere, either in the net.properties file, or by explicitly setting the system property in code, I set http.proxyHost explicitly, this will always override the System default even when java.net.useSystemProxies is set to true. java.net.useSystemProxies=true only works when the proxy is not explicitly set, and will be otherwise ignored (I have tested and verified this).

[更新 2]

如果您的最终目标只是访问 net.properties 文件的内容，您可以尝试以下操作:

If your ultimate goal is just to access the content of the net.properties file, you can try something as follows:

import java.io.IOException;
import java.io.Reader;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Properties;

public class Play {
  public static void main(String args[]) { 
    Properties props = new Properties();
    Path path = Paths.get(System.getProperty("java.home"), "lib", "net.properties");

    try (Reader r = Files.newBufferedReader(path)) {
      props.load(r);
      System.out.println("props loaded!");
    } catch (IOException x) {
      System.err.println("props failed loading!");
      x.printStackTrace(System.err);
    }
    // Now you have access to all the net.properties!
    System.out.println(props.getProperty("http.proxyHost"));
 }
}

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