Design petterns

All design paterns:
https://refactoring.guru/
https://en.wikibooks.org/wiki/Computer_Science_Design_Patterns
https://java-design-patterns.com/patterns/

Decorator pattern:
https://www.tutorialspoint.com/design_pattern/decorator_pattern.htm

Commander pattern:
https://www.youtube.com/watch?v=8gE-icd93WA

Solid principles
 S — Single Responsibility Principle
 O — Open/Closed Principle
 L — Liskov Substitution Principle
 I — Interface Segregation Principle
 D — Dependency Inversion Principle 

Kaip atvaizduojamas tekstas

image source *The Tech Train

A simbolis UTF-8 , koduojamas vienu bitu A:'1000001' 


$ echo "A" > failas.txt
$ ll failas.txt 
-rw-r--r-- 1 sup sup 2 kov.   15 09:05 failas.tx

Matome, kad failas užima 2 baitus bet kodėl? Įrašėme tik vieną simbolį, 'A' vieną baitą informacijos.

Toliau tikrinant galime pastebėti, kad

$ od -A o -t u1c failas.txt
0000000  65  10
          A  \n
0000002

Po 'A' simbolio, buvo įterptas naujos eilutės simbolis. Taigi `echo` komandą, automatiškai prideda '\n\' simbolį ir todėl failo dydis 2baitai. Panaudokime specialią `echo` vėlėvėlę

-n     do not output the trailing newline

$ echo -n "A" > failas.txt 

1 ✗ sup /tmp $ od -A o -t cd failas.txt

0000000   A

                     65

0000001

$ ls -la failas.txt 

-rw-r--r-- 1 sup sup 1 kov.   15 09:10 failas.txt


Pirmieji baitai nurodo kokio ilgio bus bitas.

0xxxxxxx - vienas bitas (maximali reikšmė 127 = 64+32+16+8+4+2+1)
110xxxxx 10xxxxx - du baitai (max reikšmė 16191)
...

(Source: https://en.wikipedia.org/wiki/UTF-8)

Tam kad naršyklėse tekstas butų teisingai atvaizduotas, reikia nustatytų žymę:

<meta charset="UTF-8">

Spring boot

Guides: https://spring.io/guides
Spring initializer: https://start.spring.io/
Docs: https://docs.spring.io/
HttpStatus Status values

REST - Representational State Transfer
DAO - Data access object (ryšys su duombaze)

model?
JSON - Javascript Object Notation

POJOS - Plain Old Java Objects
JAR - Java Archive

ORM - Object relation mapping

ODBC - Object Database Connectivity
JDBC - Java Database Connectivity

@RestController = @Controller + @ResponseBody 

 

@Service or @Component or @Repository

Running with maven

$ mvn clean package
$ mvn spring-boot:run

$ mvn clean
$ mvn install #target direktorijoje atsiras .jar failiukas
Autowiring@Autowired

GET

@GetMapping
@RequestMapping(method = RequestMethod.GET)

@GetMapping(path="/hello")
@RequestMapping(method = RequestMethod.GET, path="/hello"))

@GetMapping(path="/{name}")
public String getName(@PathVariable String name)

POST

@PostMapping()
@RequestMapping(method = RequestMethod.POST)
@ResponseStatus(HttpStatus.CREATED)

DELETE

@DeleteMapping(path = "/{username}")
@RequestMapping(path = "/{username}", method = RequestMethod.DELETE)
public void deleteUser(@PathVariable final String username) {}

application.properies

logging.level.org.springframework.web: DEBUG
logging.level.org.springframework: DEBUG
server.port=9090

spring.jackson.serialization.write-dates-as-timestamps=false

Links

Lombok in Eclipse.

Project auto refresh with devtools

Java validation annotations:
Jwt security

Swagger

http://localhost:9090/v2/api-docs
http://localhost:9090/swagger-ui.html

h2

http://localhost:8080/h2-console