How to read resource files in servlet and non-servlet entity classes

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Directory structure for Web projects

reading resource files in the servlet

public class ServletDemo6 extends HttpServlet {

/**

* ServletContext read the resource files in the Web application db.properties

**/

public void doget (HttpServletRequest request, httpservletresponse response) throws Servletexception, IOException {

/**

* Get resource Stream object by Servletcontext.getresourceasstream () method

**/

String Path = "/web-inf/classes/db.properties";

String Path = "/web-inf/classes/edu/servlet/db.properties";

String Path = "/db.properties";

getResourceAsStream (Path,response);

/**

* Access to resource stream objects through traditional file streams, but using real paths

**/

String Path = "/web-inf/classes/db.properties"; No, you need to use the real path.

String path = This.getservletcontext (). Getrealpath ("/web-inf/classes/db.properties");

FileInputStream (Path,response);

/**

* Call non-servlet class, get resource file in Userdao

**/

New Userdao (). Update1 ();

New Userdao (). Update2 ();

New Userdao (). Update (This.getservletcontext ());

}

/*

* Read the resource file to note the problem: The following traditional code is not possible, preferably using the Servletcontext.getresourceasstream () method to read

* or after the absolute path of the resource is obtained through the ServletContext Getrealpath, the resource file is read through the traditional stream

*/

private void FileInputStream (String path, httpservletresponse response) throws IOException {

FileInputStream in = new FileInputStream (path);

Properties Pros = new properties ();

Pros.load (in);

String filename = path.substring (path.lastindexof ("\") +1);

String Driver = pros.getproperty ("Driver");

String url = pros.getproperty ("url");

String username = pros.getproperty ("username");

String Password = pros.getproperty ("password");

PrintWriter out = Response.getwriter ();

OUT.PRINTLN ("filename =" +filename);

Out.println ("Driver =" +driver);

Out.println ("url =" +url);

Out.println ("username =" +username);

OUT.PRINTLN ("password =" +password);

}

private void getResourceAsStream (String path, httpservletresponse response) throws IOException {

InputStream in = This.getservletcontext (). getResourceAsStream (path);

Properties Pros = new properties ();

Pros.load (in);

String Driver = pros.getproperty ("Driver");

String url = pros.getproperty ("url");

String username = pros.getproperty ("username");

String Password = pros.getproperty ("password");

PrintWriter out = Response.getwriter ();

Out.println ("Driver =" +driver);

Out.println ("url =" +url);

Out.println ("username =" +username);

OUT.PRINTLN ("password =" +password);

}

}

reading resource files in non-servlet entity classes

public class Userdao {

/**

* This is certainly OK for the program, but it does not conform to the program design idea because the coupling between the DAO layer and the servlet layer increases,

* So should not be used in such a way, so can only use the class loader

**/

public void Update (ServletContext context) throws IOException {

InputStream in = Context.getresourceasstream ("/web-inf/classes/db.properties");

Properties Props = new properties ();

Props.load (in);

System.out.println ("url =" +props.getproperty ("url"));

}

/**

* If the program reading the resource file is not a servlet, you can only read it through the class loader

* If you use a class loader to read a resource file to generate a inputstream stream, there is also a problem, because the class loader will only load once when the service is started.

* So, when the content of Db.properties is updated, the class loader will not read the resource file until Tomcat starts again.

* So printing is still the old information, unless you redeploy the Web application (no need to restart Tomcat)

**/

public void Update1 () throws IOException {

Since the Userdao class and the db.properties are in the same directory, the class loader loads also at the same time as the Userdao classes load db.properties

InputStream in = UserDao.class.getClassLoader (). getResourceAsStream ("db.properties");

Properties Props = new properties ();

Props.load (in);

System.out.println ("url =" +props.getproperty ("url"));

}

/**

* There are two kinds of problems in the synthesis, we should solve this problem:

* Get the location of the resource file through class loading, and then read the resource file data through the traditional way (FileInputStream).

* This allows you to read the updated data

*

*

**/

public void Update2 () throws IOException {

Since the Userdao class and the db.properties are in the same directory, the class loader loads also at the same time as the Userdao classes load db.properties

String path = UserDao.class.getClassLoader (). GetResource ("Db.properties"). GetPath ();

/*

* Print: c:/program%20files/apache%20software%20foundation/tomcat%206.0/webapps/servletdetail/web-inf/classes/ Db.properties

* So this way, if there are special characters such as spaces in the path, the FileNotFoundException exception will be thrown, but the path is valid.

* or you can: accept a path parameter in the method, from the servlet through This.getservletcontext (). Getrealpath ("/web-inf/classes/db.properties") came

*/

SYSTEM.OUT.PRINTLN (path);

FileInputStream in = new FileInputStream (path);

Properties Props = new properties ();

Props.load (in);

System.out.println ("url =" +props.getproperty ("url"));

}

}