Introducing Spring Framework

Chapter 4
Using Beans Scopes
So far you have an application called My Documents that for now is exposing a service that returns either all the
documents available or it can return a list of documents by specific type. We were talking about the SearchEngine
class implementation and the way you had configured it. Based on your XML configuration, you have set its scope to
be a Singleton class, meaning that every time you require it by invoking the context.getBean method, you always
get the same instance. But what happens if you require different instances, such as another service that is required to
handle a fresh instance of your SearchEngine implementation to use its search methods.
In this chapter, I will talk about how the Spring Framework instantiates the classes and its dependencies in the
My Documents application, by using your existing code and classes such as the SearchEngine implementation. You
will see what scopes you can use and the benefits of each one.
Scopes
Right now your existing code doesn’t print out any information about what is going on, so let’s start by putting some
logs (recording activity) into your classes so you know what is happening when the Spring container creates and uses
them as shown in Listing 4-1.
Listing 4-1. SearchEngineService.java
package com.apress.isf.spring.service;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.apress.isf.java.model.Document;
import com.apress.isf.java.model.Type;
import com.apress.isf.java.service.SearchEngine;
import com.apress.isf.spring.data.DocumentDAO;
public class SearchEngineService implements SearchEngine {
private static final Logger log =
LoggerFactory.getLogger(ServiceSearchEngine.class);
private DocumentDAO documentDAO;
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