Dongwei jackblack369

A filter is an object that is invoked at the preprocessing and postprocessing of a request.

It is mainly used to perform filtering tasks such as conversion, logging, compression, encryption and decryption, input validation etc.
The servlet filter is pluggable, i.e. its entry is defined in the web.xml file, if we remove the entry of filter from the web.xml file, filter will be removed automatically and we don't need to change the servlet.

Usage of Filter

recording all incoming requests
logs the IP addresses of the computers from which the requests originate

Events are basically occurrence of something. Changing the state of an object is known as an event.

We can perform some important tasks at the occurrence of these exceptions, such as counting total and current logged-in users, creating tables of the database at time of deploying the project, creating database connection object etc.

Event classes

ServletRequestEvent
ServletContextEvent
ServletRequestAttributeEvent
ServletContextAttributeEvent

session

Session simply means a particular interval of time. Session Tracking is a way to maintain state (data) of an user. It is also known as session management in servlet.

HTTP is stateless that means each request is considered as the new request. It is shown in the figure given below:
There are four techniques used in Session tracking:
- Cookies

Web Application

HTML and HTTP

HTML:HyperText Markup Language.
HTTP:HyperText Transfer Protocol
- HTTP is the communication protocol between server and client. HTTP runs on top of TCP/IP communication protocol.
- Port numbers 0 to 1023 are reserved ports for well known services, for example 80 for HTTP, 443 for HTTPS, 21 for FTP etc.
Java Servlet and JSPs are server side technologies to extend the capability of web servers by providing support for dynamic response and data persistence.

Java 8 Functional Interfaces

Being object oriented is not bad, but it brings a lot of verbosity to the program. Java 8 Functional Interfaces and Lambda Expressions help us in writing smaller and cleaner code by removing a lot of boiler-plate code.

An interface with exactly one abstract method is called Functional Interface. @FunctionalInterface annotation is added so that we can mark an interface as functional interface.
Some of the useful java 8 functional interfaces are Consumer, Supplier, Function and Predicate.

Lambda Expression

Objects are the base of java programming language and we can never have a function without an Object, that’s why Java language provide support for using lambda expressions only with functional interfaces.
Lambda Expressions syntax is (argument) -> (body).

forEach() method in Iterable interface

default and static methods in Interfaces

Java 8 introduces the “Default Method” or (Defender methods) feature, which allows the developer to add new methods to the interfaces without breaking their existing implementation. It provides the flexibility to allow interface to define implementation which will use as the default in a situation where a concrete class fails to provide an implementation for that method.

Functional Interfaces and Lambda Expressions

Java Stream API for Bulk Data Operations on Collections

Java Time API

Collection API improvements

Concurrency API improvements

自从用了网易云，我把《故事会》退订了
¿Why?

public class

public class Main {
 
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
    public class Test1 {}  //正确
}
public class Test2{}//错误

	import java.util.Arrays;
	import java.util.List;

	import org.hibernate.Query;
	import org.hibernate.Session;
	import org.hibernate.SessionFactory;
	import org.hibernate.Transaction;

	import com.journaldev.hibernate.model.Employee;
	import com.journaldev.hibernate.util.HibernateUtil;

	import java.util.Arrays;
	import java.util.List;

	import org.hibernate.Criteria;
	import org.hibernate.FetchMode;
	import org.hibernate.Session;
	import org.hibernate.SessionFactory;
	import org.hibernate.Transaction;
	import org.hibernate.criterion.Order;
	import org.hibernate.criterion.ProjectionList;