java8新特性练习JAVA8新特性快速写入和读取文件

导读JAVA8快速读取和写文件话不多说，先看题：随机生成Salary{name,baseSalary,bonus}的记录，如“wxxx,10,1”，每行一条记录....

JAVA8快速读取和写文件

话不多说，先看题：

随机生成 Salary {name, baseSalary, bonus }的记录，如“wxxx,10,1”，每行一条记录，总共1000万记录，写入文本文件（UFT-8编码）， 然后读取文件，name的前两个字符相同的，其年薪累加，比如wx，100万，3个人，最后做排序和分组，输出年薪总额最高的10组：

name 4位a-z随机，baseSalary [0,100]随机 bonus[0-5]随机 ，年薪总额 = baseSalary*13 bonus。

思路：

第一步：先编写一个Salary对象

里面包含有name，baseSalary, bounus属性，然后编写一个构造器，重写toString()方法方便序列化数据，同时编写构建Salary对象的方法build()；

/** * name 4位a-z随机 * baseSalary 0-100随机 * bonus 0-5随机 * 年薪总额 = baseSalary * 13 bonus */class Salary { // name 4位a-z随机,baseSalary 0-100随机,bonus 0-5随机 年薪总额 = baseSalary * 13 bonus private String name; private int baseSalary; private int bonus; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getBaseSalary() { return baseSalary; } public void setBaseSalary(int baseSalary) { this.baseSalary = baseSalary; } public int getBonus() { return bonus; } public void setBonus(int bonus) { this.bonus = bonus; } public Salary() { } public Salary(String name, int baseSalary, int bonus) { this.name = name; this.baseSalary = baseSalary; this.bonus = bonus; } public Salary build() { this.name = getRandomName(4); // 0-100随机数 this.baseSalary = (int)(100 * Math.random()); // 0-5随机数 this.bonus = (int)(5 * Math.random()); return this; } @Override public String toString() { return name " " baseSalary " " bonus; } /** * 生产Name随机函数 4位a-z随机 * @param length * @return */ private static String getRandomName(int length ){ String base = "abcdefghijklmnopqrstuvwxyz"; Random random = new Random(); StringBuffer sb = new StringBuffer(); for ( int i = 0; i < length; i ){ int number = random.nextInt(base.length()); sb.append(base.charAt(number)); } return sb.toString(); }}

第二步：编写写入方法

a) 第一种方式，使用Java的IO中BufferedWriter写入文件

/** * 写入文件 * @return * @throws IOException */public static File writeBuffer() throws IOException { File file = new File(FILE_NAME); FileOutputStream fos = new FileOutputStream(file); BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(fos)); int i = AMOUNT; while(i > 0) { Salary salary = new Salary().build(); writer.write(salary.toString() "\r\n"); i --; } writer.close(); fos.close(); return file;}

b) 第二种方式，使用JAVA的NIO中的FileChannel进行写入

/** * NIO进行写入 * @throws IOException */private static void writeNIO() throws IOException { FileOutputStream fos = new FileOutputStream(FILE_NAME, true); FileChannel channel = fos.getChannel(); int i = AMOUNT; StringBuffer content = new StringBuffer(); while(i > 0) { Salary salary = new Salary().build(); content.append(salary.toString()).append("\r\n"); i --; } ByteBuffer buf = ByteBuffer.wrap(content.toString().getBytes()); buf.put(content.toString().getBytes()); buf.flip(); channel.write(buf); channel.close(); fos.close();}

比较下来，单纯从这个代码的性能上讲差不太多！

第三步：读取并解析文件在进行排序

a) 通过JAVA的IO进行读取：

/** * Java IO读取文件的方式 * @return * @throws Exception */public static List<Salary> readFileIO() throws Exception { File file = new File(FILE_NAME); List<Salary> list = new ArrayList<>(); InputStreamreader reader = new InputStreamReader(new FileInputStream(file)); // 建立一个输入流对象reader BufferedReader br = new BufferedReader(reader); // 建立一个对象，它把文件内容转成计算机能读懂的语言 String line = ""; // 每一行的内容 int i = 1; while ((line = br.readLine()) != null) { String[] split = line.trim().split(" ");// .trim()可以去掉首尾多余的空格 list.add(new Salary(split[0], Integer.valueOf(split[1]), Integer.valueOf(split[2]))); // 添加一个Salary实体 i ; } reader.close(); br.close(); return list;}

b) 通过JAVA的NIO读取：

/** * JDK8 NIO读取文件 * @return * @throws Exception */public static List<Salary> readFileNIO() throws Exception { List<Salary> list = new ArrayList<>(); Files.lines(Paths.get(FILE_NAME)).forEach(line -> { String[] split = line.trim().split(" ");// .trim()可以去掉首尾多余的空格 list.add(new Salary(split[0], Integer.valueOf(split[1]), Integer.valueOf(split[2]))); // 添加一个Salary实体 }); return list;}

二者比较下来：使用jdk1.8读取更简单，效率性能更高！

第四步：使用JDK8的Stream进行排序和截取

/** * 排序并获取前十数据 * @param salaries */public static void sort(List<Salary> salaries) { Map<String, GroupSalary> result = new HashMap<>(); salaries.forEach(salary -> { String shortName = salary.getName().substring(0, 2); GroupSalary groupSalary = null; List<Salary> salaryList = null; if (result.containsKey(shortName)) { groupSalary = result.get(shortName); salaryList = groupSalary.getSalaries(); } else { groupSalary = new GroupSalary(); salaryList = new ArrayList<>(); groupSalary.setSalaries(salaryList); } salaryList.add(salary); groupSalary.setShortName(shortName); groupSalary.setTotal(groupSalary.getTotal() salary.getBaseSalary() * 13 salary.getBonus()); result.put(shortName, groupSalary); }); List<GroupSalary> r = result.entrySet().stream() .sorted((Map.Entry<String, GroupSalary> o1, Map.Entry<String, GroupSalary> o2) -> o2.getValue().getTotal() - o1.getValue().getTotal()) .map(entry -> entry.getValue()).collect(Collectors.toList()).subList(0,10); r.forEach(groupSalary -> { System.out.println(groupSalary.getShortName() " " groupSalary.getTotal() " " groupSalary.getSalaries().size()); });}

同时将数据封装在GroupSalary中

class GroupSalary { private List<Salary> salaries; private String shortName; private int total; public List<Salary> getSalaries() { return salaries; } public void setSalaries(List<Salary> salaries) { this.salaries = salaries; } public String getShortName() { return shortName; } public void setShortName(String shortName) { this.shortName = shortName; } public int getTotal() { return total; } public void setTotal(int total) { this.total = total; }}

到此如果写入100W数据基本上1分钟不到就可以完成写入和读取，欢迎大家进行改写和优化。