从 java 类中的 web.xml 读取值
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Read the value from web.xml in a java class
提问by Sebastian
I have a Web Application with a web.xml file and some java classes that I build with Maven. At some point I want to get in the java class a parameter from the web.xml file.
我有一个带有 web.xml 文件的 Web 应用程序和一些我用 Maven 构建的 java 类。在某些时候，我想在 java 类中从 web.xml 文件中获取一个参数。
How can I read the value in a normal java class, not a Servlet ?
如何读取普通 java 类而不是 Servlet 中的值？
回答by Sebastian
I found the solution for this and actually you have to declare some env-entry tags in the web.xml like this :
我找到了解决方案，实际上你必须在 web.xml 中声明一些 env-entry 标签，如下所示：
<env-entry>
<env-entry-name>properties-file</env-entry-name>
<env-entry-type>java.lang.String</env-entry-type>
<env-entry-value>Property</env-entry-value>
</env-entry>
In your java class you have to import the Context and NamingException (this was in my case, i am not sure if this applies to others) :
在您的 java 类中，您必须导入 Context 和 NamingException （这是在我的情况下，我不确定这是否适用于其他人）：
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
and where you want to get the value you must do it like this :
以及您想要获得价值的地方，您必须这样做：
Context ctx = new InitialContext();
Context env = (Context) ctx.lookup("java:comp/env");
final String fileName = (String) env.lookup("properties-file");
Hopefully this helps others too :-)
希望这对其他人也有帮助:-)
回答by Sampada
Add an init-param in your web.xml like this -
像这样在 web.xml 中添加一个 init-param -
<init-param>
<param-name>myParam</param-name>
<param-value>myParamValue</param-value>
</init-param>
You can access this in your code using -
您可以使用 - 在您的代码中访问它
getServletContext().getInitParameter("myParam")
回答by Somebody
Even simpler:
更简单：
web.xml:
网页.xml：
<env-entry>
<env-entry-name>properties-file</env-entry-name>
<env-entry-type>java.lang.String</env-entry-type>
<env-entry-value>Property</env-entry-value>
</env-entry>
java class:
java类：
InitialContext initialContext = new InitialContext();
String fileName = (String) initialContext.lookup("java:comp/env/properties-file");
回答by Sandeep Sukhija
You can read the XML file using the Properties object.
您可以使用 Properties 对象读取 XML 文件。
Sample code on how to load the xml is mentioned below:
下面提到了有关如何加载 xml 的示例代码：
File file = new File("test.xml");
FileInputStream fileInput = new FileInputStream(file);
Properties properties = new Properties();
properties.loadFromXML(fileInput);
fileInput.close();
Once the file is loaded, now you can fetch the properties using properties.getProperty("keyname");
加载文件后，现在您可以使用获取属性 properties.getProperty("keyname");
回答by Hodglem
I had a similar challenge; I won't go into detail but suffice it to say that I was trying to circumvent having an environment variable to set logback logging paths. This isn't the solution I went with, but it does locate and read in web.xml and allows you to grab variables. It uses JDOM2 so you could pretty much read whatever you wanted.
我也遇到过类似的挑战；我不会详细介绍，但足以说明我试图绕过环境变量来设置 logback 日志记录路径。这不是我采用的解决方案，但它确实在 web.xml 中定位和读取，并允许您获取变量。它使用 JDOM2，因此您几乎可以阅读任何您想要的内容。
private String getLogLocation() throws JDOMException, IOException {
SAXBuilder jdomBuilder = new SAXBuilder();
String logLocation = null;
Document jdomDocument = jdomBuilder.build(this.getFilePath());
Element webXMLRoot = jdomDocument.getRootElement();
List<Element> elements = webXMLRoot.getChildren();
for (Element e : elements) {
for (Element childElement : e.getChildren()) {
System.out.println(childElement.getQualifiedName());
if (childElement.getValue().equals("logLocation")) {
logLocation = e.getChild("env-entry-value",childElement.getNamespace()).getValue();
break;
}
}
}
return logLocation;
}
private String getFilePath() {
String classPath = LoggerStartupListener.class.getProtectionDomain().getCodeSource().getLocation().getPath();
classPath = classPath.replace("classes", "");
classPath = classPath + "web.xml";
return classPath;
}
回答by nyname00
You can use XPathto find the element you're interested in, e.g.
您可以使用XPath来查找您感兴趣的元素，例如
DocumentBuilder builder = DocumentBuilderFactory
.newInstance()
.newDocumentBuilder();
Document doc = builder.parse(file);
XPath xpath = XPathFactory
.newInstance()
.newXPath();
XPathExpression expr = xpath.compile("/web-app/servlet/servlet-name[text()='MyServlet']");
NodeList nl = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
Edit: based on your comments, here' a way to get the file handle to your web.xml. Note that, without a ServletContextit depends on from where you are calling this. So this might not work in your case, but you can tweak it to get the file.
编辑：根据您的评论，这是一种获取web.xml文件句柄的方法。请注意，如果没有 a，ServletContext则取决于您从何处调用它。因此，这可能不适用于您的情况，但您可以对其进行调整以获取文件。
File clsLocation = new File(getClass()
.getProtectionDomain()
.getCodeSource()
.getLocation()
.getFile());
String webXml = clsLocation
.getCanonicalPath()
.replaceAll("WEB-INF.*", "WEB-INF/web.xml");
File file = new File(webXml);
// use 'file' with the code above and change the XPath to the element you want to read
