Plantuml第一步

慢慢发现在诸多技能中，coding不应该花很多时间。 在代码编写前，和代码编写后的事情，往往才是需要花大量时间的。 想清楚你要做什么，要怎么做，以及之后要达成什么样的目标，检验结果是否符合预期 这些事情，都应该比coding要重要。不然准备不充分，上来就写代码，是不可持续的。 想写一系列的pre coding 和 post coding 的文章。今天开个头，希望能持续写下去

UML–让你的需求清晰的法宝

首先说明，我不用图形界面拖拽控件来画流程图。诸如Visio、 Precess On我一律不用。
原因很简单，我认为拖拽的效率非常低，你大量的精力都花在元素是否对其，鼠标点点点和键盘输入之间来回切换,你反而不能集中精力去思考逻辑。还有一个原因，不利于复用和修改。

Plantuml

plantuml是一个开源的工具，你可以用它来画流程图，用例图 类图等等。最令人满意的是，你可以用写代码的模式来“画”uml图。 比如：

1.创建一个demo.uml的文件,用你习惯的编辑器，编写如下内容：

    @startuml
    client->server: syn=1 seq=x
    note left
        客户端发送syn报文,
        发送序列号为x
    end note
    client<-server: syn=1 ack=x+1 seq=y
    note right
        服务端接受请求， 回复syn+ack报文，
        并置发送序列号为y,确认序列号为x+1
    end note
    client->server: ack=y+1 seq=z
    note left
        客户端发送ack报文,并置发送序列号为z
        确认序列号为y+1
    end note
    @enduml

2.下载plantuml.jar包

 http://sourceforge.net/projects/plantuml/files/plantuml.jar/download

3.把plantuml.jar移动到你乐意的路径下,并创建一个可执行文件plantuml文件

    linux下参考如下操作:
    mv ./plantuml.jar   /usr/local/bin/plantuml.jar
    touch /usr/local/bin/plantuml
    echo "#!/bin/bash" >> /usr/local/bin/plantuml
    echo "jar -jar /usr/local/bin/plantuml.jar $@" >> /usr/local/bin/plantuml
    chmod +x  /usr/local/bin/plantuml 

4.查看plantuml的帮助plantuml -h,结果如下

Usage: java -jar plantuml.jar [options] -gui
    (to execute the GUI)
    or java -jar plantuml.jar [options] [file/dir] [file/dir] [file/dir]
    (to process files or directories)

You can use the following wildcards in files/dirs:
    *    means any characters but '/'
    ?    one and only one character but '/'
    **    means any characters (used to recurse through directories)

where options include:
    -gui        To run the graphical user interface
    -tpng        To generate images using PNG format (default)
    -tsvg        To generate images using SVG format
    -teps        To generate images using EPS format
    -tpdf        To generate images using PDF format
    -tvdx        To generate images using VDX format
    -txmi        To generate XMI file for class diagram
    -tscxml        To generate SCXML file for state diagram
    -thtml        To generate HTML file for class diagram
    -ttxt        To generate images with ASCII art
    -tutxt        To generate images with ASCII art using Unicode characters
    -tlatex        To generate images using LaTeX/Tikz format
    -tlatex:nopreamble    To generate images using LaTeX/Tikz format without preamble
    -o[utput] "dir"    To generate images in the specified directory
    -DVAR1=value    To set a preprocessing variable as if '!define VAR1 value' were used
    -Sparam1=value    To set a skin parameter as if 'skinparam param1 value' were used
    -r[ecurse]        recurse through directories
    -I/path/to/file    To include file as if '!include file' were used
    -I/path/to/*.puml    To include files with pattern
    -charset xxx    To use a specific charset (default is UTF-8)
    -e[x]clude pattern    To exclude files that match the provided pattern
    -metadata        To retrieve PlantUML sources from PNG images
    -nometadata        To NOT export metadata in PNG/SVG generated files
    -checkmetadata        Skip PNG files that don't need to be regenerated
    -version        To display information about PlantUML and Java versions
    -checkversion    To check if a newer version is available for download
    -v[erbose]        To have log information
    -quiet        To NOT print error message into the console
    -debugsvek        To generate intermediate svek files
    -h[elp]        To display this help message
    -testdot        To test the installation of graphviz
    -graphvizdot "exe"    To specify dot executable
    -p[ipe]        To use stdin for PlantUML source and stdout for PNG/SVG/EPS generation
    -encodesprite 4|8|16[z] "file"    To encode a sprite at gray level (z for compression) from an image
    -computeurl|-encodeurl    To compute the encoded URL of a PlantUML source file
    -decodeurl        To retrieve the PlantUML source from an encoded URL
    -syntax        To report any syntax error from standard input without generating images
    -language        To print the list of PlantUML keywords
    -checkonly        To check the syntax of files without generating images
    -failfast        To stop processing as soon as a syntax error in diagram occurs
    -failfast2        To do a first syntax check before processing files, to fail even faster
    -pattern        To print the list of Regular Expression used by PlantUML
    -duration        To print the duration of complete diagrams processing
    -nbthread N        To use (N) threads for processing
    -nbthread auto    To use 4 threads for processing
    -timeout N        Processing timeout in (N) seconds. Defaults to 15 minutes (900 seconds).
    -author[s]        To print information about PlantUML authors
    -overwrite        To allow to overwrite read only files
    -printfonts        To print fonts available on your system
    -enablestats    To enable statistics computation
    -disablestats    To disable statistics computation (default)
    -htmlstats        To output general statistics in file plantuml-stats.html
    -xmlstats        To output general statistics in file plantuml-stats.xml
    -realtimestats    To generate statistics on the fly rather than at the end
    -loopstats        To continuously print statistics about usage
    -splash        To display a splash screen with some progress bar
    -progress        To display a textual progress bar in console
    -pipeimageindex N    To generate the Nth image with pipe option
    -stdlib        To print standard library info
    -extractstdlib    To extract PlantUML Standard Library into stdlib folder
    -filename "example.puml"    To override %filename% variable
    -preproc        To output preprocessor text of diagrams
    -cypher        To cypher texts of diagrams so that you can share them

If needed, you can setup the environment variable GRAPHVIZ_DOT.

5.把刚才写的uml文件输出为png或其他格式plantuml -tpng test.uml图片如下：

总结

推荐给大家使用，vs code 等编辑器都用plantuml的插件，可以非常方便地预览uml图。
用写代码的方法来画图，可以做到手脑同步。后续打算把很多知识点用plantuml画出来，把源码开源出来，大家一起学习。也有可能踩到坑，但是蛮期待的。
当然，我用的是vim ^_^