The handwritten spring instantiation bean source code only implements the Object getBean(String beanId) method.
That is to achieve:
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("xxx");
Object o = applicationContext.getBean("xxx");
//Define ApplicationContext interface:
public interface ApplicationContext {<!-- -->
Object getBean(String name);
}
// ClassPathXmlApplicationContext class
/**
* Parse xml files, read tags, and instantiate objects
* @param springPath spring.xml path
*/
import org.w3c.dom.Document;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.InputStream;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class ClassPathXmlApplicationContext implements ApplicationContext{<!-- -->
private final Map<String, Object> beanObjects = new HashMap<>();
public ClassPathXmlApplicationContext(String springPath) {<!-- -->
// Parse the spring configuration file, then instantiate the Bean and put the Bean into beanObjects
try {<!-- -->
// Parse xml file by path
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
// Get the spring configuration file under the classpath
InputStream in = ClassLoader.getSystemClassLoader().getResourceAsStream(springPath);
Document document = db.parse(in);
// Get all Bean tags
NodeList beans = document.getElementsByTagName("bean");
//System.out.println(beans.getLength());
for (int i = 0; i < beans.getLength(); i + + ) {<!-- -->
// Get the name and value of all attributes of a certain bean tag and store them in the map collection
NamedNodeMap attributes = beans.item(i).getAttributes();
// Get the id in the bean tag
String beanId = attributes.getNamedItem("id").getNodeValue();
// Get the class in the bean tag
String classValue = attributes.getNamedItem("class").getNodeValue();
//System.out.println(beanId);
//System.out.println(classValue);
// Create objects through reflection mechanism and expose them in advance
Class<?> beanClazz = Class.forName(classValue);
//Create object through constructor method
Object beanObject = beanClazz.getConstructor().newInstance();
// Expose the bean
beanObjects.put(beanId, beanObject);
// System.out.println(beanObject);
}
//Traverse all bean tags again and assign values to properties
for (int i = 0; i < beans.getLength(); i + + ) {<!-- -->
// Get the name and value of all attributes of a certain bean tag and store them in the map collection
NamedNodeMap attributes = beans.item(i).getAttributes();
// Get the id in the bean tag
String beanId = attributes.getNamedItem("id").getNodeValue();
// Get the class in the bean tag
String classValue = attributes.getNamedItem("class").getNodeValue();
// Get all property tags under the bean tag. Note that this contains a carriage return and needs to be filtered.
NodeList childNodes = beans.item(i).getChildNodes();
List<Node> propertyNodes = new ArrayList<>();
for(int j=0; j<childNodes.getLength(); j + + ){<!-- -->
if (childNodes.item(j).getAttributes() !=null) {<!-- -->
propertyNodes.add(childNodes.item(j));
}
// If it is a carriage return, this will be null
//System.out.println(childNodes.item(j).getAttributes());
}
// Get the name and value attributes of the property attribute or the name and ref attributes
if (propertyNodes.size() != 0) {<!-- -->
propertyNodes.forEach(propertyNode -> {<!-- -->
// Get the attribute name and attribute value map of the property tag
NamedNodeMap propertyNodeAttributes = propertyNode.getAttributes();
// Get the name attribute value
Node nameNode = propertyNodeAttributes.getNamedItem("name");
// Get the value attribute value
Node valueNode = propertyNodeAttributes.getNamedItem("value");
// Get the ref attribute
Node refNode = propertyNodeAttributes.getNamedItem("ref");
//Assign a value to the object instantiated by the bean tag
// Get the created object from beanObjects based on beanId
Object beanObject = beanObjects.get(beanId);
if (nameNode != null & amp; & amp; valueNode != null) {<!-- -->
try {<!-- -->
// Splicing set method
String name = nameNode.getNodeValue();
String value = valueNode.getNodeValue();
String setMethod = "set" + name.toUpperCase().charAt(0) + name.substring(1);
// Call the set method through reflection mechanism
Class<?> clazz1 = Class.forName(classValue);
Method method = clazz1.getDeclaredMethod(setMethod, String.class);
method.invoke(beanObject, value);
} catch (ClassNotFoundException e) {<!-- -->
e.printStackTrace();
} catch (NoSuchMethodException e) {<!-- -->
e.printStackTrace();
} catch (InvocationTargetException e) {<!-- -->
e.printStackTrace();
} catch (IllegalAccessException e) {<!-- -->
e.printStackTrace();
}
}
if (nameNode != null & amp; & amp; refNode != null){<!-- -->
try {<!-- -->
// Splicing set method
String name = nameNode.getNodeValue();
String ref = refNode.getNodeValue();
String setMethod = "set" + name.toUpperCase().charAt(0) + name.substring(1);
//System.out.println(setMethod);
// Find the corresponding beanObject based on ref
Object refObject = beanObjects.get(ref);
//System.out.println(refObject.getClass().getName());
// Call method using reflection mechanism
Class.forName(classValue).getDeclaredMethod(setMethod, refObject.getClass()).invoke(beanObject, refObject);
} catch (IllegalAccessException e) {<!-- -->
e.printStackTrace();
} catch (InvocationTargetException e) {<!-- -->
e.printStackTrace();
} catch (NoSuchMethodException e) {<!-- -->
e.printStackTrace();
} catch (ClassNotFoundException e) {<!-- -->
e.printStackTrace();
}
}
});
}
}
} catch (Exception e) {<!-- -->
e.printStackTrace();
}
}
@Override
public Object getBean(String name) {<!-- -->
return beanObjects.get(name);
}
}