Question

how can i load data into memory with a tomcat server ?

i have a java class that load data from a file.
i want to load the data into memory once and that every time the client request a page that uses that class the data will be used from the memory.

for example

class MyClass
{
      HashMap data = new HashMap(100);
      public void LoadDataFromFile()
      {.....}
      public void UseTheData(String input)
      {....}
      public MyClass(){ LoadDataFromFile();}  // c'tor load data
      public SetInput(String Input)
      {
           UseTheData(input);
      }
}

and in my jsp file

Myclass myclass= new MyCass();
myclass.LoadDataFromFile();
myclass.UseTheData();

i know i should use JSTL in the jsp file

if i use the scope=”session” will the data loading will remain ?

<jsp:useBean id="myclass" class="MyClass" scope="session">
<jsp:setProperty name="myclass" property="input" value="blabla" />
</jsp:useBean>

if i do the data loading in the constructor, can i make sure the class is init only once ?

Answer 1

Create a ServletContextListener and register it in your web.xml file. In the ServletContextListener, when the application is initialized, read the file and store it in an attribute of the ServletContext. This attribute is then easily accessible from your Java and JSP code.