Spring boot hot swapping

Hot swapping is a productive feature for your development, which helps to reload classes automatically without restarting container.

The only setting is to add below into your pom.xml, as it is said here.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <optional>true</optional>
</dependency>

Applications that use spring-boot-devtools will automatically restart whenever files on the classpath change.

Now,

  1. mvn spring-boot:run & to launch your application background.

  2. edit a java file in vim and save it.

    Nothing happens?!

    Don’t panic, that’s right, spring-boot-devtools watches only files on the classpath as mentioned above. The last step is to build your java source file to propagate changes to classpath such as target/classes.

  3. mvn compile

    You could see your application automatically restarted. If you’are using IDE, this step could be mitigated by enabling automatic build.

As a vim user, I don’t use IDE even when coding with Java, here is the way I facilitate quick build from vim.

Add below into your ~/.vim/ftplugin/java.vim.

function! SearchFileBackwards(fn)
    let fp = expand('%:p')
    let pos = len(fp) - 1
    while pos > 0
        let pom = ""
        if fp[pos] == '/'
            let pom = strpart(fp, 0, pos + 1) . a:fn
            if filereadable(pom)
                break
            endif
        endif
        let pos = pos - 1
    endwhile
    return pom
endfunction

function! BuildMavenProject()
    let pom = SearchFileBackwards("pom.xml")
    if pom != ""
        exec '!mvn -f '.SearchFileBackwards("pom.xml").' compile'
    else
        echohl WarningMsg | echo "No pom.xml found." | echohl None
    endif
endfunction

" comment out below line to enable automatic build on maven project.
" autocmd BufWritePost *.java :call BuildMavenProject()

" Press <F8> to build current maven project.
nnoremap <buffer> <silent> <F8> :call BuildMavenProject()<CR>
github.com/brookhong