向文件写入文本

File file = new File("out.txt")

file.write "First line\n"
file << "Second line\n"
file.append("hello\n")

println file.text

获取文件全部内容

File file = new File('examples/data/count_digits.txt')

// 获取文件全部内容
println file.getText('UTF-8')
println file.text

// 获得文件的输入流
def inputStream = file.newInputStream()

遍历文件的全部行

File file = new File("/path/to/file")

// 第一种方法

def lines = file.readLines()
for (line in lines) {
    // ...
}

// 第二种方法

file.eachLine { line, nb ->
    println "Line $nb: $line"
}

参考文献

WikiNotes/操作文件（读取、写入）
Groovy: reading and writing files - appending content
Working with IO
How to read a file in Groovy into a string? - Stack Overflow