---
# System prepended metadata

title: Java Reusable Code Snippets
tags: [' programming language', ' Java', Software Engineer]

---

---
tags: Software Engineer, programming language, Java, 
---

# Java Reusable Code Snippets


## Handle Nullable List with Optional.
```java
Optional.ofNullable()
    orElse(Collections.emptyList())
    // do map, filter, functional stuff here ...
```

```java
Optional.ofNullable(x) 
    .map(...) // if optional of null gets mapped, what happens?
    .orElseGet(...)
    
```

Optional.of()
  .map
  .orElse()

Instant, Duration, Period, LocalDate, LocalDateTime


## Spring

injection syntax
- field injection
- setter injection
- constructor injection





lombok `UtilityClass`
toBuilder


retry


## SQL snippets

check tables & columns in Oracle.



time processing snippets


window function
https://www.postgresql.org/docs/current/tutorial-window.html



mapstruct mapper `qualifiedNyName`



What is Generics type.


Use `?`
`Function<A, ?>`

TestNG, validating the flow throws exception

use `expectThrows`, don't use try catch and assert exception.




spring batch concepts




