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Spring Bean Scope

Spring Bean has four scopes,

• singleton

  Singleton instance per Spring IoC container. This is the default.

• prototype

  Scopes a single bean definition to any number of object instances. That means, every time, it requires to inject the bean or the getBean method is called.

Spring Understanding

I first learnt Spring in 2008 when I was a student, and I remember that day had a verify famous pattern named SSH, that including,

• Spring

  Spring is used for manage beans, compared with EJB way, it's very easy for a beginner like me to learn and use.

• Struts

  Apache Struts was used for MVC, although, it's outdated with current Spring MVC, but in that time, it's much better than using JSPs.

• Hibernate

  Hibernate is never changed, it's always used as an ORM

After many years experience with Spring, and Spring boot, I am coming up with my mind,

Java Stream Guide

Assume we have the following classes,

@Data
public class User {
  private long id;
  private String name;
  private int age;

  private List<Address> address;
}


@Data
public class Address {
  private String postCode;
  private String street;
  private String building;
}

Inject Properties From YAML in Spring

In Spring, we can easily define configuration value in a YAML file, and inject those configuration into a Java class.

Take the following the YAML configuration file as an example.

server: localhost

# by default, spring split the string with comma
listValues: a,b,c,d
# if we want to split the string with customize character, we can use Spring EL
listValuesWithSpEL: a,b;c,d;e,f

# we can inject the whole complexObject into another class, with annotation ConfigurationProperties
complexObject:
    port: 90
    ssl: false
    listValues: a,b,c,d
    listValuesWithSpEL: a,b;c,d;e,f

RSQL JPA ClassCastException with Spring JPA AbstractPersistable

What are RSQL and RSQL JPA?

RSQL is a query language for parametrized filtering of entries in RESTful APIs. It’s based on FIQL (Feed Item Query Language) – an URI-friendly syntax for expressing filters across the entries in an Atom Feed.

RSQL JPA translates RSQL query into org.springframework.data.jpa.domain.Specification or com.querydsl.core.types.Predicate and support entities association query.

Mock Class Property in PyTest

It's easy to use Mock for a python method, staticmethod, classmethod, but for propery, it's not just to use Mock. Here are the example to mock a property of a class in python UT.

• A simple class

  Python

  class Dog:
      @property
      def name(self):
          return "dog"
  

Spring Security Authorization Filter

Spring Security supports to easily configure role or authority for a specified resource by using Spring security expression.

For example,

@Bean
public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
    ...
    .antMatchers("/auth/admin/*").hasRole("ADMIN")
    .antMatchers("/auth/*").hasAnyRole("ADMIN","USER")
    ...
}

What are PO, VO, DAO, BO, POJO, DTO in Java

Definition

Switch Fallthrough in Go

If you are familar with C or Java, you must know that break is requird for a switch's case branch, if break is missed, then it will fall through to next case.

For example, consider the following code

int a = 1;

switch (a) {
    case 0: System.out.println("0");
    case 1: System.out.println("1");
    case 2: System.out.println("2"); break;
    default: System.out.println("unknown"); break;
}

The output is:

1
2

Java Virtual Thread Usage

What is Virtual thread?

A Java platform thread is mapped to OS Kernel thread, as the resource is limited, we can't create as many as platform threads as we want.

Even Java provides executor pool, it also can't handle some cases. For example, if we want to create thoudsands of IO tasks, virtual threads is more suitable than platform threads.