How a JAR file can read an external properties file

Question

We have a connection pooling component (JAR file) for one of our application. As of now the application connection details are bundled with-in the JAR file (in .properties file).

Can we make it more generic? Can we have the client tell the properties file details (both the path and the file name) and use the JAR to get the connection?

Does it make sense to have something like this in the client code:

XyzConnection con = connectionIF.getConnection(uname, pwd);

Along with this, the client will specify (somehow???) the properties file details that has the URLs to connect, timeout etc.

Answer 1

Simplest way, use the -D switch to define a system property on a java command line. That system property may contain a path to your properties file.

Eg

java -cp ... -Dmy.app.properties=/path/to/my.app.properties my.package.App

Then, in your code you can do ( exception handling is not shown for brevity ):

String propPath = System.getProperty( "my.app.properties" );

final Properties myProps;

if ( propPath != null )
{
     final FileInputStream in = new FileInputStream( propPath );

     try
     {
         myProps = Properties.load( in );
     }
     finally
     {
         in.close( );
     }
}
else
{
     // Do defaults initialization here or throw an exception telling
     // that environment is not set
     ...
}

Answer 2

http://www.javaworld.com/javaworld/javaqa/2003-08/01-qa-0808-property.html

multiple approaches are available, the article above provides more details

 ClassLoader.getResourceAsStream ("some/pkg/resource.properties");
 Class.getResourceAsStream ("/some/pkg/resource.properties");
 ResourceBundle.getBundle ("some.pkg.resource");

Answer 3

Just load the properties from file, something like

Properties properties = new Properties();
InputStreamReader in = null;
try {
     in = new InputStreamReader(new FileInputStream("propertiesfilepathandname"), "UTF-8");
     properties.load(in);
} finally {
     if (null != in) {
         try {
             in.close();
         } catch (IOException ex) {}
     }
}

Note how the encoding is explicitly specified as UTF-8 above. It could also be left out if you accept the default ISO8859-1 encoding, but beware with any special characters then.

Answer 4

This is my solution. First looking for app.properties in startup folder, if does not exists try to load from your JAR package:

File external = new File("app.properties");
if (external.exists())
    properties.load(new FileInputStream(external));
else 
    properties.load(Main.class.getClassLoader().getResourceAsStream("app.properties"));

Answer 5

Simplest way is below. It will load application.properties from cfg folder outside of the jar file.

Directory Structure

  |-cfg<Folder>-->application.properties
  |-somerunnable.jar

Code:

    Properties mainProperties = new Properties();
    mainProperties.load(new FileInputStream("./cfg/application.properties"));
    System.out.println(mainProperties.getProperty("error.message"));

Answer 6

In netbeans I needed to load application.properties from conf/ folder outside of the jar file.

Therefore I wrote :

public static String getProperty(String FileName, String Prop)
{   

    try {  
        FIS = new FileInputStream( "./../conf/"+FileName);
        Properties properties;
        (properties = new Properties()).load(FIS);          

        for(Enumeration propKeys = properties.propertyNames();
                propKeys.hasMoreElements();){
            String tmpKey = (String) propKeys.nextElement();
            String tmpValue = properties.getProperty(tmpKey);                   

            tmpValue = tmpValue.trim();
            if (tmpKey.equals(Prop)){
                //System.out.println(tmpKey +"="+tmpValue);
                properties.put(tmpKey, tmpValue);
                Value = properties.getProperty(Prop);
                break;
            }

        }

        if (Value==null){
            throw new Exception("La Propiedad : "+Prop+" no Se encuentra en el Archivo de Configuracion");
        } 

    } catch (IOException e) {
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return Value;

}

For Eclipse apply the following:

FIS = new FileInputStream( "../conf/"+FileName);

Answer 7

public static String getPropertiesValue(String propValue) {
        Properties props = new Properties();
        fileType = PCLLoaderLQIOrder.class.getClassLoader().getResourceAsStream(propFileName);
        if (fileType != null) {
            try {
                props.load(fileType);
            } catch (IOException e) {
                logger.error(e);
            }
        } else {
            try {
                throw new FileNotFoundException("Property file" + propFileName + " not found in the class path");
            } catch (FileNotFoundException e) {
                logger.error(e);
            }
        }
        String propertiesValue = props.getProperty(propValue);
        return propertiesValue;
    }

above methods works for me, just store your property file into directory from where to run your jar and provide that name in place of propFileName, when you want any value from property just call getPropertyValue("name") .