groovy - 如何制作“StringWriterMarkupBuilder”

Question

如何创建一个类型，它是 aMarkupBuilder但具有用 a 初始化的默认构造函数StringWriter并覆盖以toString()调用？toString()StringWriter

思路如下，当然不允许在调用超级构造函数之前初始化实例变量：

class StringWriterMarkupBuilder extends MarkupBuilder {
    final def sw = new StringWriter()
    StringWriterMarkupBuilder() {
        super(sw)
    }

    @Override String toString() {
        sw.toString()
    }
}

Answer 1

抱歉，我终于通过深入研究 MarkupBuilder 的 Groovy 源代码找到了解决方案！：

class StringWriterMarkupBuilder extends MarkupBuilder {
    StringWriterMarkupBuilder() {
        //MarkupBuilder.this(new IndentPrinter(new PrintWriter(writer)))
        super(new StringWriter()) 
    }

    @Override String toString() {
        //IndentPrinter.PrintWriter.StringWriter
        return super.getPrinter().out.out.toString()
    }
}

Answer 2

You could also do this with the metaClass like so:

import groovy.xml.MarkupBuilder

MarkupBuilder createSWMB() {
  new StringWriter().with { sw ->
    new MarkupBuilder( sw ).with { mb ->
      mb.metaClass.toString = { -> sw.toString() }
      mb
    } 
  }
}

MarkupBuilder mb = createSWMB()
mb.root {
  names {
    name( first:'tim', second:'yates' )
  }
}
println mb.toString()