Groovy Tip 34 Groovy语言的here-docs
??????????????Groovy Tip 34 Groovy语言的here-docs ? ? ? Groovy语言对Java字符串的改变,除了String对象的很多新功能,最大的好处就是引入了Gstring的概念,这些都在前面的文字中有过详细的阐述。除此之外,Groovy语言还引入了here-docs的概念,这就是本篇将要谈到的。 简单来说,here-docs就是用来解决字符串换行的问题。 在Java语言中,字符串换行有两种解决方法。 一种是通过"+"号连接,这种本身对字符串没有换行,因为字符串本身太长,通过换行来方便我们的阅读。这种场合最常用的是sql语句。如下: ??? private static final String sql = "select t.qdbid as itemdbid,"+ ?????????????????????????????????????? "t.itemtype as itemlev,"+ ?????????????????????????????????????? "t.itemname as itemname,"+ ?????????????????????????????????????? "t.sourceid as parentid "+ ?????????????????????????????????????? "from t_sp_qcddvbase t "+ ?????????????????????????????????????? "where t.yearmonth=? and "+ ?????????????????????????????????????? "t.isview LIKE '%Y%' "+? ?????????????????????????????????????? "order by t.itemtype,t.qdbid"; ? ? 我们可能都写过了类似于上面的sql语句,在上面的语句中,为了方便我们的阅读,我们不得不为了一句sql语句,输入多个"+"号,还有多对引号。这大大的降低了我们的编码效率。同时,由于每一行的字符串都需要引号和"+"号连接,所以阅读性也并不是太好。 在Groovy语言中,我们引入了here-docs的概念,所谓"here-docs",在Groovy语言中,就是由三对双引号引起来的,可以换行的字符串。例如,使用"here-docs",我们就可以把上面的sql语句写成下面的样子: ??? private static final String sql = """select t.qdbid as itemdbid, ??????????????????????????????? ? ? ?t.itemtype as itemlev, ??????????????????????????????? ? ? ?t.itemname as itemname, ??????????????????????????????? ? ? ?t.sourceid as parentid? ??????????????????????????????? ? ? ?from t_sp_qcddvbase t ??????????????????????????????? ? ? ?where t.yearmonth=? and ??????????????????????????????? ? ? ?t.isview LIKE '%Y%'?? ??????????????????????????????? ?? ?order by t.itemtype,t.qdbid"""; ??? ? 可以看到,使用"here-docs"的阅读性就比上面的Java语言的方式要强得多。而且编码也方便了很多。 同时,"here-docs"中的换行也是字符串中的真正换行。曾经,我们在Java语言中要用到字符串的换行,就必须借助于"/n"字符串。比如,一个网上书店的通知单的编码可能是如下的样子: ? ? ?????? ? String name = "Wallace"; ?????? ? ?????? ? String sex = "male"; ?????? ? ?????? ? String[] books = new String[]{"Groovy in action","Grails in action"}; ??? ??? ?????? ? String time = "2009-05-20"; ?????? ? ?????? ? StringBuffer sb = new StringBuffer(); ?????? ? ?????? ? sb.append("Dear "); ?????? ? if("male".equalsIgnoreCase(sex)) ?????? ? { ?????????? ? sb.append("Mr."); ?????? ? } ?????? ? else if("female".equalsIgnoreCase(sex)) ?????? ? { ?????????? ? sb.append("Ms."); ?????? ? } ?????? ? sb.append(name).append(",/n? "); ?????? ? ?????? ? sb.append("You has bought "); ?????? ? ?????? ? sb.append(books.length).append(" books: "); ?????? ? ?????? ? for(int i=0;i<books.length;i++) ?????? ? { ?????????? ? sb.append(books[i]).append(","); ?????? ? } ?????? ? ?????? ? sb.append("? You will receive it at ").append(time); ?????? ? sb.append("/n"); ?????? ? sb.append("? Thank You!"); ?????? ? ?????? ? System.out.println(sb.toString()); ??? ? 运行结果为: Dear Mr.Wallace, ? You has bought 2 books: Groovy in action,Grails in action,? You will receive it at 2009-05-20 ? Thank You! ? 可以看到,编码十分的繁琐,代码的阅读性也很差。如果使用"here-docs"的话,编码将会是如下的样子: ? ?????? ? String name = "Wallace" ?????? ? ?????? ? String sex = "male" ?????? ? ?????? ? String[] books = ["Groovy in action","Grails in action"] ??? ??? ?????? ? String time = "2009-05-20" ?????? ? ?????? ? def mrms = sex=='male'?'Mr':'Ms' ????????????? ? ?????? ? def bookNames = books.join(',') ?????? ? ?????? ? def letter = """Dear ${mrms}.${name}, ? You has bought ${books.size()} books: ${bookNames},? You will receive it at $time ? Thank You!""" ???????????????????? ? ?????? ?println letter ??? ? 运行结果为: Dear Mr.Wallace,? You will receive it at 2009-05-20 ? Thank You! ? ? 可以看到,由于"here-docs"也支持Gstring,所以使用"here-docs"对多行字符串进行编码,无论是代码量上,还是可读性上,都强了很多。 最后,值得注意的是,由于"here-docs"也是字符串,同样可以进行字符串的各种操作,请看如下的一个生成html标签的代码: ? ??? ? def list = ['Groovy in action','Grails in action'] ??? ? ??? ? def name = 'select1' ??? ? ??? ? def select = """<select name="${name}"> """ ?? ??? ? StringBuffer sb = new StringBuffer() ? ?????? list.each{ ?????????? sb <<"? <option>${it}</option>/n" ?????? } ? ??? ? select = select+sb.toString() ??? ? ??? ? select = select+ """ </select>""" ? ? println select ? ? 里面既有"here-doc",又有双引号的字符串加上Gstring,然后再把它们连接起来,整个编码显得十分的灵活。 运行结果为: <select name="select1"> ? <option>Groovy in action</option> ? <option>Grails in action</option> ? </select> (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |