Simple ways to keep data on redeployment of Java EE 7 web application

Question

My Java EE 7 web service generates statistics once per day, and because data is stored only in an ApplicationScoped bean, it does not survive redeployment, so clients cannot ret

Answer 1

In the @ApplicationScoped bean, you can just implement @PreDestroy to save it to some temporary storage which you then check and read in @PostConstruct. You can get the container-managed temporary storage location as a servlet context attribute keyed by ServletContext.TEMPDIR.

Here's a kickoff example using JAXB so that the data is saved in reusable XML format.

private Data data;
private File file;
private JAXBContext jaxb;

@Inject
private ServletContext servletContext;

@PostConstruct
public void init() {
    File tempdir = (File) servletContext.getAttribute(ServletContext.TEMPDIR);
    file = new File(tempdir, "data.xml");
    jaxb = JAXBContext.newInstance(Data.class);

    if (file.exists()) {
        data = (Data) jaxb.createUnmarshaller().unmarshal(file);
    }
}

@PreDestroy
public void destroy() {
    jaxb.createMarshaller().marshal(data, file);
}

If you happen to deploy to JBoss (WildFly), then you can alternatively also use JBoss-managed data folder, which is a bit more permanent than the location as represented by ServletContext.TEMPDIR.

String datadir = System.getProperty("jboss.server.data.dir");
file = new File(datadir, "data.xml");