关于java:JAVA基础知识String以及文件目录读取

String根底

String s = "Hello World!";s.chars().mapToObj(letter -> (char)letter)        .map(Character::toUpperCase)        .forEach(System.out::print);        //输入        HELLO WORLD!

StringBuffer是同步的，StringBuilder是不同步的，因而StringBuilder执行速度更快
JDK7当前的String的+操作曾经通过了StringBuilder编译，因而执行速度也很快，不必再必须应用StringBuilder或者StringBuffer了

//读取文件并输入发现的第一个Spring的行try(BufferedReader bf = new BufferedReader(new FileReader(new File("/Users/username/Documents/git_code/course/pom.xml")))){    Stream<String> stream = bf.lines();    stream.filter(line -> line.contains("Spring"))            .findFirst()            .ifPresent(System.out::println);}catch(Exception e){}//输入    <description>Demo project for Spring Boot</description>

另一种读取

Path path = Paths.get("/Users","/username/Documents/git_code/course/","pom.xml");try(Stream<String> stream = Files.lines(path)){    stream.filter(line -> line.contains("Spring"))            .findFirst()            .ifPresent(System.out::println);}catch(Exception e){}//输入   <description>Demo project for Spring Boot</description>

读取文件目录Files.list

Path path = Paths.get("/Users","/username/Documents/git_code/course/");try(Stream<Path> stream = Files.list(path)){    stream.filter(p -> p.toFile().isDirectory())            .forEach(System.out::println);}catch(Exception e){}//输入/Users/username/Documents/git_code/course/target/Users/username/Documents/git_code/course/.mvn/Users/username/Documents/git_code/course/.idea/Users/username/Documents/git_code/course/src

遍历文件目录Files.walk

Path path = Paths.get("/Users","/username/Documents/git_code/course/");try(Stream<Path> stream = Files.walk(path)){    stream.filter(p -> p.toFile().isDirectory())            .forEach(System.out::println);}catch(Exception e){}//输入/Users/username/Documents/git_code/course/Users/username/Documents/git_code/course/target/Users/username/Documents/git_code/course/target/generated-sources/Users/username/Documents/git_code/course/target/generated-sources/annotations/Users/username/Documents/git_code/course/target/classes/Users/username/Documents/git_code/course/target/classes/static/Users/username/Documents/git_code/course/target/classes/templates/Users/username/Documents/git_code/course/target/classes/templates/pdf/Users/username/Documents/git_code/course/.mvn/Users/username/Documents/git_code/course/.mvn/wrapper/Users/username/Documents/git_code/course/.idea/Users/username/Documents/git_code/course/.idea/libraries/Users/username/Documents/git_code/course/src

遍历指定层级目录Files.walk

Path path = Paths.get("/Users","/username/Documents/git_code/course/");try(Stream<Path> stream = Files.walk(path, 2)){    stream.filter(p -> p.toFile().isDirectory())            .forEach(System.out::println);}catch(Exception e){}//输入/Users/username/Documents/git_code/course/Users/username/Documents/git_code/course/target/Users/username/Documents/git_code/course/target/generated-sources/Users/username/Documents/git_code/course/target/classes/Users/username/Documents/git_code/course/.mvn/Users/username/Documents/git_code/course/.mvn/wrapper/Users/username/Documents/git_code/course/.idea/Users/username/Documents/git_code/course/.idea/libraries/Users/username/Documents/git_code/course/src/Users/username/Documents/git_code/course/src/test/Users/username/Documents/git_code/course/src/main