Mock up the logic of ApplicationContext in spring

Description:

Mock up how spring container initializes the beans from property file.

A simple mock-up. Just consider that no other property files imported.

package com.jesse.spring.containermockup.utils;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.log4j.Logger;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.XPath;
import org.dom4j.io.SAXReader;
import com.jesse.spring.containermockup.model.BeanDefinition;
public class MockupClassPathXMLApplicationContext {
private List<BeanDefinition> beanDefinitions = new ArrayList<BeanDefinition>();
private Map<String, Object> singletons = new HashMap<String, Object>();
private static final Logger logger = Logger.getLogger(MockupClassPathXMLApplicationContext.class);
public MockupClassPathXMLApplicationContext(String filename) {
this.readXML(filename);
initBeans();
logger.info("beanDefinitions.size == >> " + beanDefinitions.size());
}
public void initBeans() {
for(BeanDefinition beanDefinition : beanDefinitions) {
try {
singletons.put(beanDefinition.getId(), Class.forName(beanDefinition.getClassName()).newInstance());
} catch (InstantiationException | IllegalAccessException
| ClassNotFoundException e) {
e.printStackTrace();
}
}
}
public Object getBean(String name) {
if(singletons.size() > 0) {
return singletons.get(name);
}
return null;
}
public void readXML(String filename) {
try {
SAXReader saxReader = new SAXReader();
URL xmlPath = this.getClass().getClassLoader().getResource(filename);
Document document = saxReader.read(xmlPath);
Map<String,String> nsMap = new HashMap<String,String>();
nsMap.put("ns", "http://www.springframework.org/schema/beans");
XPath xsub = document.createXPath("//ns:beans/ns:bean");
xsub.setNamespaceURIs(nsMap);
@SuppressWarnings("unchecked")
List<Element> beans = xsub.selectNodes(document);
for(Element element : beans) {
String id = element.attributeValue("id");
String clazz = element.attributeValue("class");
BeanDefinition beanDefinition = new BeanDefinition(id, clazz);
beanDefinitions.add(beanDefinition);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}