一、概述
Guava是对Java API的补充,对Java开发中常用功能进行更优雅的实现,使得编码更加轻松,代码容易理解。Guava使用了多种设计模式,同时经过了很多测试,得到了越来越多开发团队的青睐。Java最新版本的API采纳了Guava的部分功能,但依旧无法替代。本文以Getting Started With Google Guava原文为学习材料,对Guava中常用的API进行学习,尽量覆盖比较有用的API,包括字符串处理,集合类处理,文件IO处理等。
二、字符串连接器Joiner
2.1 连接多个字符串并追加到StringBuilder
- StringBuilder stringBuilder = new StringBuilder("hello");
- // 字符串连接器,以|为分隔符,同时去掉null元素
- Joiner joiner1 = Joiner.on("|").skipNulls();
- // 构成一个字符串foo|bar|baz并添加到stringBuilder
- stringBuilder = joiner1.appendTo(stringBuilder, "foo", "bar", null, "baz");
- System.out.println(stringBuilder); // hellofoo|bar|baz
2.2 连接List元素并写到文件流
- FileWriter fileWriter = null;
- try{
- fileWriter = new FileWriter(new File("/home/gzx/Documents/tmp.txt"));
- }
- catch(Exception e){
- System.out.println(e.getMessage());
- }
- List<Date> dateList = new ArrayList<Date>();
- dateList.add(new Date());
- dateList.add(null);
- dateList.add(new Date());
- // 构造连接器:如果有null元素,替换为no string
- Joiner joiner2 = Joiner.on("#").useForNull("no string");
- try{
- // 将list的元素的tostring()写到fileWriter,是否覆盖取决于fileWriter的打开方式,默认是覆盖,若有true,则是追加
- joiner2.appendTo(fileWriter, dateList);
- // 必须添加close(),否则不会写文件
- fileWriter.close();
- }
- catch(IOException e){
- System.out.println(e.getMessage());
- }
最后tmp.txt的内容为:
Tue Dec 20 16:51:09 CST 2016#no string#Tue Dec 20 16:51:09 CST 2016
2.3 将Map转化为字符串
- Map<String, String> testMap = Maps.newLinkedHashMap();
- testMap.put("Cookies", "12332");
- testMap.put("Content-Length", "30000");
- testMap.put("Date", "2016.12.16");
- testMap.put("Mime", "text/html");
- // 用:分割键值对,并用#分割每个元素,返回字符串
- String returnedString = Joiner.on("#").withKeyValueSeparator(":").join(testMap);
- System.out.println(returnedString); // Cookies:12332#Content-Length:30000#Date:2016.12.16#Mime:text/html
三、 字符串分割器Splitter
3.1 将字符串分割为Iterable
- // 分割符为|,并去掉得到元素的前后空白
- Splitter sp = Splitter.on("|").trimResults();
- String str = "hello | world | your | Name ";
- Iterable<String> ss = sp.split(str);
- for(String it : ss){
- System.out.println(it);
- }
结果为:
hello
world
your
Name
world
your
Name
3.2 将字符串转化为Map
- // 内部类的引用,得到分割器,将字符串解析为map
- Splitter.MapSplitter ms = Splitter.on("#").withKeyValueSeparator(':');
- Map<String, String> ret = ms.split(returnedString);
- for(String it2 : ret.keySet()){
- System.out.println(it2 + " -> " + ret.get(it2));
- }
结果为:
Cookies -> 12332
Content-Length -> 30000
Date -> 2016.12.16
Mime -> text/html
Content-Length -> 30000
Date -> 2016.12.16
Mime -> text/html
四、 字符串工具类Strings
- System.out.println(Strings.isNullOrEmpty("")); // true
- System.out.println(Strings.isNullOrEmpty(null)); // true
- System.out.println(Strings.isNullOrEmpty("hello")); // false
- // 将null转化为""
- System.out.println(Strings.nullToEmpty(null)); // ""
- // 从尾部不断补充T只到总共8个字符,如果源字符串已经达到或操作,则原样返回。类似的有padStart
- System.out.println(Strings.padEnd("hello", 8, 'T')); // helloTTT
五、字符匹配器CharMatcher
5.1 空白一一替换
- // 空白回车换行对应换成一个#,一对一换
- String stringWithLinebreaks = "hello world\r\r\ryou are here\n\ntake it\t\t\teasy";
- String s6 = CharMatcher.BREAKING_WHITESPACE.replaceFrom(stringWithLinebreaks,'#');
- System.out.println(s6); // hello#world###you#are#here##take#it###easy
5.2 连续空白缩成一个字符
- // 将所有连在一起的空白回车换行字符换成一个#,倒塌
- String tabString = " hello \n\t\tworld you\r\nare here ";
- String tabRet = CharMatcher.WHITESPACE.collapseFrom(tabString, '#');
- System.out.println(tabRet); // #hello#world#you#are#here#
5.3 去掉前后空白和缩成一个字符
- // 在前面的基础上去掉字符串的前后空白,并将空白换成一个#
- String trimRet = CharMatcher.WHITESPACE.trimAndCollapseFrom(tabString, '#');
- System.out.println(trimRet);// hello#world#you#are#here
5.4 保留数字
- String letterAndNumber = "1234abcdABCD56789";
- // 保留数字
- String number = CharMatcher.JAVA_DIGIT.retainFrom(letterAndNumber);
- System.out.println(number);// 123456789
六、 断言工具类Preconditions
- // 检查是否为null,null将抛出异常IllegalArgumentException,且第二个参数为错误消息。
- trimRet = null;
- //Preconditions.checkNotNull(trimRet, "label can not be null");
- int data = 10;
- Preconditions.checkArgument(data < 100, "data must be less than 100");
七、对象工具类 Objects
7.1 Objects的toStringHelper和hashCode方法
- // Book用Objects的相关方法简化toString(),hashCode()的实现。
- // 用ComparisonChain简化compareTo()(Comparable接口)方法的实现。
- Book book1 = new Book();
- book1.setAuthor("Tom");
- book1.setTitle("Children King");
- book1.setIsbn("11341332443");
- System.out.println(book1);
- System.out.println(book1.hashCode());
- Book book2 = new Book();
- book2.setAuthor("Amy");
- book2.setTitle("Children King");
- book2.setIsbn("111");
- System.out.println(book2);
- System.out.println(book2.hashCode());
- System.out.println(book1.compareTo(book2));
结果为:
Book{author=Tom, title=Children King, isbn=11341332443, price=0.0}
268414056
Book{author=Amy, title=Children King, isbn=111, price=0.0}
-1726402621
1
268414056
Book{author=Amy, title=Children King, isbn=111, price=0.0}
-1726402621
1
7.2 Objects的firstNonNull方法
- // 如果第一个为空,则返回第二个,同时为null,将抛出NullPointerException异常
- String someString = null;
- String value = Objects.firstNonNull(someString, "default value");
- System.out.println(value); // deafult value
Book.java
- class Book implements Comparable<Book>{
- private String author;
- private String title;
- private String publisher;
- private String isbn;
- private double price;
- public String getAuthor() {
- return author;
- }
- public void setAuthor(String author) {
- this.author = author;
- }
- public String getTitle() {
- return title;
- }
- public void setTitle(String title) {
- this.title = title;
- }
- public String getPublisher() {
- return publisher;
- }
- public void setPublisher(String publisher) {
- this.publisher = publisher;
- }
- public String getIsbn() {
- return isbn;
- }
- public void setIsbn(String isbn) {
- this.isbn = isbn;
- }
- public double getPrice() {
- return price;
- }
- public void setPrice(double price) {
- this.price = price;
- }
- // 定义第一二关键字
- @Override
- public int compareTo(Book o) {
- return ComparisonChain.start().compare(this.title, o.title).compare(this.isbn, o.isbn).result();
- }
- public String toString(){
- return Objects.toStringHelper(this).omitNullValues().add("author", author).add("title", title)
- .add("publisher", publisher).add("isbn", isbn).add("price", price).toString();
- }
- public int hashCode(){
- return Objects.hashCode(author, title, publisher, isbn, price);
- }
- }
八、整体迭代接口FluentIterable
8.1 使用Predicate整体过滤
- Person person1 = new Person("Wilma", 30, "F");
- Person person2 = new Person("Fred", 32, "M");
- Person person3 = new Person("Betty", 32, "F");
- Person person4 = new Person("Barney", 33, "M");
- List<Person> personList = Lists.newArrayList(person1, person2, person3, person4);
- // 过滤年龄大于等于32的person
- Iterable<Person> personsFilteredByAge =
- FluentIterable.from(personList).filter(new Predicate<Person>() {
- @Override
- public boolean apply(Person input) {
- return input.getAge() > 31;
- }
- });
- // Iterable有一个iterator方法,集合类都有一个Iterator方法
- for(Iterator<Person> it = personsFilteredByAge.iterator(); it.hasNext();){
- System.out.println(it.next());
- }
- System.out.println(Iterables.contains(personsFilteredByAge, person2));
结果为:
Person{name='Fred', sex='M', age=32}
Person{name='Betty', sex='F', age=32}
Person{name='Barney', sex='M', age=33}
true
Person{name='Betty', sex='F', age=32}
Person{name='Barney', sex='M', age=33}
true
8.2 使用Function整体替换,将List<Person>转化为List<String>
- // 将List<Person> 转化为 List<String>,数据源为personList。整体迭代。
- List<String> transformPersonList = FluentIterable.from(personList).transform(
- new Function<Person, String>(){
- @Override
- public String apply(Person person) {
- // 不定参数,返回String类型
- return Joiner.on("#").join(person.getName(), person.getSex(), person.getAge());
- }
- }
- ).toList();
- for(int i = 0; i < transformPersonList.size(); i++){
- System.out.println(transformPersonList.get(i));
- }
结果为:
Wilma#F#30
Fred#M#32
Betty#F#32
Barney#M#33
Person.java
- class Person{
- private String name;
- private String sex;
- private int age;
- public Person(String name, int age, String sex){
- this.name = name;
- this.sex = sex;
- this.age = age;
- }
- public String getName() {
- return name;
- }
- public void setName(String name) {
- this.name = name;
- }
- public String getSex() {
- return sex;
- }
- public void setSex(String sex) {
- this.sex = sex;
- }
- public int getAge() {
- return age;
- }
- public void setAge(int age) {
- this.age = age;
- }
- @Override
- public String toString() {
- return "Person{" +
- "name='" + name + '\'' +
- ", sex='" + sex + '\'' +
- ", age=" + age +
- '}';
- }
- }
九、 集合运算工具类Sets
9.1 集合差
- // s1 - s2
- Set<String> s1 = Sets.newHashSet("1", "2", "3", "4");
- Set<String> s2 = Sets.newHashSet("2", "3", "4", "5");
- // 得到第一个集合中有而第二个集合没有的字符串
- Sets.SetView res = Sets.difference(s1, s2);
- for(Iterator<String> it = res.iterator(); it.hasNext();){
- System.out.println(it.next()); // 1
- }
9.2 集合对称差
- Sets.SetView res2 = Sets.symmetricDifference(s1, s2);
- for(Object it14 : res2){
- System.out.println(it14); // 1 5
- }
9.3 集合交
- // s1和s2的交集
- Sets.SetView<String> res3 = Sets.intersection(s1, s2);
- for(String it14 : res3){
- System.out.println(it14); // 2 3 4
- }
9.4 集合并
- // 合并s1和s2
- Sets.SetView<String> res4 = Sets.union(s1, s2);
- for(String it14 : res4){
- System.out.println(it14); // 1 2 3 4 5
- }
十、Function和Predicate
10.1 利用Functions将Map转化为Function
- Map<String, Person> mp = Maps.newHashMap();
- mp.put(person1.getName(), person1);
- mp.put(person2.getName(), person2);
- mp.put(person3.getName(), person3);
- mp.put(person4.getName(), person4);
- // 将map转化为Function,Function的功能是将一个类型转化为另一个类型
- Function<String, Person> lookup = Functions.forMap(mp);
- // 如果键值不存在,则会抛出异常。lookup内部已经有元素
- Person tmp = lookup.apply("Betty");
- System.out.println(tmp == person3); // true
10.2 Predicate单个判断
- Predicate<Person> agePre = new Predicate<Person>(){
- @Override
- public boolean apply(Person person) {
- return person.getAge() < 32;
- }
- };
- Predicate<Person> namePre = new Predicate<Person>(){
- @Override
- public boolean apply(Person person) {
- return person.getName().equals("Betty");
- }
- };
- // 判断是否符合条件
- System.out.println(agePre.apply(person2)); // false
- System.out.println(agePre.apply(person3)); // false
- System.out.println(namePre.apply(person2)); // false
- System.out.println(namePre.apply(person3)); // true
10.3 Predicates的and运算
- // 利用Predicates工具类,同时满足两个条件成一个predicate
- Predicate<Person> both = Predicates.and(agePre, namePre);
- System.out.println(both.apply(person1)); // false
- System.out.println(both.apply(person3)); // false
10.4 Predicates的or运算
- // 至少一个满足组成一个Predicate
- Predicate<Person> orPre = Predicates.or(agePre, namePre);
- System.out.println(orPre.apply(person2)); // false
10.5 Predicates的compose运算
- // 通过键name获得值Person,然后检查Person的age < 32,即agepre.apply(lookup.apply(name)) == true?
- // lookup内部已经有集合
- Predicate<String> two = Predicates.compose(agePre, lookup);
- System.out.println(two.apply("Wilma")); // true
十一、 Map工具类Maps
- // 将List<Person> 转化为Map<String, Person>,其中键值对是person.name -> Person
- Map<String, Person> myMp = Maps.uniqueIndex(personList.iterator(), new Function<Person, String>(){
- // name作为person的键
- @Override
- public String apply(Person person) {
- return person.getName();
- }
- });
- for(String name : myMp.keySet()){
- System.out.println(myMp.get(name));
- }
结果为:
Person{name='Wilma', sex='F', age=30}
Person{name='Fred', sex='M', age=32}
Person{name='Betty', sex='F', age=32}
Person{name='Barney', sex='M', age=33}
Person{name='Fred', sex='M', age=32}
Person{name='Betty', sex='F', age=32}
Person{name='Barney', sex='M', age=33}
十二、一键多值类Multimap
12.1 数组存储多值类ArrayListMultimap
- // 用ArrayList保存,一键多值,值不会被覆盖
- ArrayListMultimap<String, String> multimap = ArrayListMultimap.create();
- multimap.put("foo", "1");
- multimap.put("foo", "2");
- multimap.put("foo", "3");
- multimap.put("bar", "a");
- multimap.put("bar", "a");
- multimap.put("bar", "b");
- for(String it20 : multimap.keySet()){
- // 返回类型List<String>
- System.out.println(it20 + " : " + multimap.get(it20));
- }
- // 返回所有ArrayList的元素个数的和
- System.out.println(multimap.size());
结果为:
bar : [a, a, b]
foo : [1, 2, 3]
6
foo : [1, 2, 3]
6
12.2 HashTable存储多值类 HashMultimap
- //这里采用HashTable保存
- HashMultimap<String, String> hashMultimap = HashMultimap.create();
- hashMultimap.put("foo", "1");
- hashMultimap.put("foo", "2");
- hashMultimap.put("foo", "3");
- // 重复的键值对值保留一个
- hashMultimap.put("bar", "a");
- hashMultimap.put("bar", "a");
- hashMultimap.put("bar", "b");
- for(String it20 : hashMultimap.keySet()){
- // 返回类型List<String>
- System.out.println(it20 + " : " + hashMultimap.get(it20));
- }
- // 5
- System.out.println(hashMultimap.size());
结果为:
bar : [a, b]
foo : [1, 2, 3]
5
foo : [1, 2, 3]
5
十三、多键类Table
13.1 两个键操作
- // 两个键row key和column key,其实就是map中map, map<Integer, map<Integer, String> > mp
- HashBasedTable<Integer, Integer, String> table = HashBasedTable.create();
- table.put(1, 1, "book");
- table.put(1, 2, "turkey");
- table.put(2, 2, "apple");
- System.out.println(table.get(1, 1)); // book
- System.out.println(table.contains(2, 3)); // false
- System.out.println(table.containsRow(2)); // true
- table.remove(2, 2);
- System.out.println(table.get(2, 2)); // null
13.2 获取一个Map
- // 获取单独的一个map
- Map<Integer, String> row = table.row(1);
- Map<Integer, String> column = table.column(2);
- System.out.println(row.get(1)); // book
- System.out.println(column.get(1)); // turkey
十四、 可以通过value获取key的HashBiMap
14.1 value不可以有相同的key
- BiMap<String, String> biMap = HashBiMap.create();
- // value可以作为Key,即value不可以有多个对应的值
- biMap.put("hello", "world");
- biMap.put("123", "tell");
- biMap.put("123", "none"); // 覆盖tell
- // biMap.put("abc", "world"); 失败
- // 下面是强制替换第一对
- biMap.forcePut("abc", "world");
- System.out.println(biMap.size()); // 2
- System.out.println(biMap.get("hello"));// null
- System.out.println(biMap.get("abc")); // world
- System.out.println(biMap.get("123")); // none
14.2 键值对互换得到新的BiMap
- // 键值对互换
- BiMap<String, String> inverseMap = biMap.inverse();
- System.out.println(inverseMap.get("world")); // abc
- System.out.println(inverseMap.get("tell")); // null
- System.out.println(inverseMap.get(null)); // null
十五、不可变集合类ImmutableListMultimap
- // 不可变的集合,都有一个Builder内部类。不可以修改和添加
- Multimap<Integer, String> map = new ImmutableListMultimap.Builder<Integer, String>().put(1, "hello")
- .putAll(2, "abc", "log", "in").putAll(3, "get", "up").build();
- System.out.println(map.get(2)); // [abc, log, in]
十六、 区间工具类Range
- // 闭区间
- Range<Integer> closedRange = Range.closed(30, 33);
- System.out.println(closedRange.contains(30)); // true
- System.out.println(closedRange.contains(33)); // true
- // 开区间
- Range<Integer> openRange = Range.open(30, 33);
- System.out.println(openRange.contains(30)); // false
- System.out.println(openRange.contains(33)); // false
- Function<Person, Integer> ageFunction = new Function<Person, Integer>(){
- @Override
- public Integer apply(Person person) {
- return person.getAge();
- }
- };
- // Range实现了Predicate接口,这里的第一个参数是Predicate,第二个参数是Function
- // ageFunction必须返回整数
- Predicate<Person> agePredicate = Predicates.compose(closedRange, ageFunction);
- System.out.println(agePredicate.apply(person1)); // person1.age == 30 true
十七、比较器工具类 Ordering
17.1 逆置比较器
- // 自定义比较器,嵌入式的比较器,匿名类。注意这里有两个person参数,与Comparable的区别
- Comparator<Person> ageCmp = new Comparator<Person>(){
- // Ints是Guava提供的,递增
- @Override
- public int compare(Person o1, Person o2) {
- return Ints.compare(o1.getAge(), o2.getAge());
- }
- };
- List<Person> list = Lists.newArrayList(person1, person2, person3, person4);
- // 将比较器转化为Ordering,得到比较器ageCmp的相反比较器,递减
- Collections.sort(list, Ordering.from(ageCmp).reverse());
- for(Iterator<Person> iter = list.iterator(); iter.hasNext(); ){
- System.out.println(iter.next());
结果为:
Person{name='Barney', sex='M', age=33}
Person{name='Fred', sex='M', age=32}
Person{name='Betty', sex='F', age=32}
Person{name='Wilma', sex='F', age=30}
Person{name='Fred', sex='M', age=32}
Person{name='Betty', sex='F', age=32}
Person{name='Wilma', sex='F', age=30}
17.2 组合多个比较器
- // 按照名字排序
- Comparator<Person> nameCmp = new Comparator<Person>(){
- @Override // 两个对象,而Comparable是this和一个对象
- public int compare(Person o1, Person o2) {
- return o1.getName().compareTo(o2.getName());
- }
- };
- // 组合两个比较器,得到第一二排序关键字
- // 年龄相同时按照名字排序
- Ordering order = Ordering.from(ageCmp).compound(nameCmp);
- Collections.sort(list, order);
- for(Iterator<Person> iter = list.iterator(); iter.hasNext(); ){
- System.out.println(iter.next());
- }
结果为:
Person{name='Wilma', sex='F', age=30}
Person{name='Betty', sex='F', age=32}
Person{name='Fred', sex='M', age=32}
Person{name='Barney', sex='M', age=33}
17.3 直接获取最小几个和最大几个
- Ordering order2 = Ordering.from(nameCmp);
- // 最小的两个,无序
- System.out.println("least 2...");
- List<Person> least = order2.leastOf(personList, 2);
- for(int i = 0; i < 2; i++){
- System.out.println(least.get(i));
- }
- // 最大的三个,无序
- System.out.println("greatest 3....");
- List<Person> great = order2.greatestOf(personList, 3);
- for(int i = 0; i < 3; i++){
- System.out.println(great.get(i));
- }
结果为:
least 2...
Person{name='Barney', sex='M', age=33}
Person{name='Betty', sex='F', age=32}
greatest 3....
Person{name='Wilma', sex='F', age=30}
Person{name='Fred', sex='M', age=32}
Person{name='Betty', sex='F', age=32}
Person{name='Barney', sex='M', age=33}
Person{name='Betty', sex='F', age=32}
greatest 3....
Person{name='Wilma', sex='F', age=30}
Person{name='Fred', sex='M', age=32}
Person{name='Betty', sex='F', age=32}
十八、 文件工具类Files
18.1 复制移动重命名文件
- // 文件操作:复制,移动,重命名
- File originFile = new File("/home/gzx/Documents/Program/Java/abc.java");
- File copyFile = new File("/home/gzx/Documents/test.java");
- File mvFile = new File("/home/gzx/Documents/abc.java");
- try {
- Files.copy(originFile, copyFile);
- Files.move(copyFile, mvFile); // 重命名
- }
- catch(IOException e){
- e.printStackTrace();
- }
18.2 获取文件哈希码
- try {
- // File,HashFunction
- HashCode hashCode = Files.hash(originFile, Hashing.md5());
- System.out.println(originFile.getName() + " : " + hashCode);
- } catch (IOException e) {
- e.printStackTrace();
- }
结果为:abc.java : 66721c8573de09bd17bafac125e63e98
18.3 读取文件流,将文件行转化为List
- // 读文件流
- int lineNumber = 1;
- try {
- // 读出所有的行到list中,去掉\n
- List<String> list2 = Files.readLines(mvFile, Charsets.UTF_8);
- for(Iterator<String> it = list2.iterator(); it.hasNext();){
- System.out.println("line " + lineNumber + ":" + it.next());
- lineNumber++;
- }
- } catch (IOException e) {
- e.printStackTrace();
- }
结果为:
line 1:public class test{
line 2: static String str;
line 3: public static void main(String[] args){
line 4:
line 5: System.out.println(str);
line 6: }
line 7:}
18.4 将文件行进行处理,再得到List
- // LineProcessor处理每一行,得到返回值
- /*
- 内容:
- Linux命令行大全,人民邮电出版社
- Linux内核完全注释,机械工业出版社
- Linux命令行和shell脚本编程大全,人民邮电出版社
- */
- File bookFile = new File("/home/gzx/Documents/book.txt");
- try {
- // 只取书名
- List<String> list3 = Files.readLines(bookFile, Charsets.UTF_8, new TitleLineProcessor());
- for(Iterator<String> it = list3.iterator(); it.hasNext();){
- System.out.println(it.next());
- }
- } catch (IOException e) {
- e.printStackTrace();
- }
结果为:
Linux命令行大全
Linux内核完全注释
Linux命令行和shell脚本编程大全
18.5 写文件流
- // 写文件流
- File writeFile = new File("/home/gzx/Documents/write.txt");
- try {
- // 不必打开或关闭文件流,会自动写盘
- Files.write("hello world!", writeFile, Charsets.UTF_8); // 重新写
- Files.append("你的名字", writeFile, Charsets.UTF_8); // 追加
- } catch (IOException e) {
- e.printStackTrace();
- }
write.txt的内容为
hello world!你的名字
TitleLineProcessor.java
- class TitleLineProcessor implements LineProcessor<List<String>>{
- private final static int INDEX = 0;
- private final static Splitter splitter = Splitter.on(",");
- private List<String> titles = new ArrayList<String>();
- // 每一行都会调用这个函数,进而追加成一个list
- @Override
- public boolean processLine(String s) throws IOException {
- // 获取第一项,并追加到titles
- titles.add(Iterables.get(splitter.split(s), INDEX));
- return true;
- }
- // 最终的结果
- @Override
- public List<String> getResult() {
- return titles;
- }
- }
十九、 读输入字节流ByteSource和写输出字节流ByteSink
- // source是源的意思,封装输入流
- ByteSource byteSource = Files.asByteSource(writeFile);
- try {
- byte[] contents1 = byteSource.read();
- byte[] contents2 = Files.toByteArray(writeFile); // 两个方法的作用相同
- for(int i = 0; i < contents1.length; i++){
- assert(contents1[i] == contents2[i]);
- System.out.print(contents1[i] + " ");
- }
- } catch (IOException e) {
- e.printStackTrace();
- }
- // sink是目的地的意思,封装输出流,流会自动关闭
- File tmpFile = new File("/home/gzx/Documents/hello.txt"); // acd
- ByteSink byteSink = Files.asByteSink(tmpFile);
- try {
- byteSink.write(new byte[]{'a', 'c', 'd', '\n'});
- } catch (IOException e) {
- e.printStackTrace();
- }
二十、 编码工具类BaseEncoding
- File pdfFile = new File("/home/gzx/Documents/google.pdf");
- BaseEncoding baseEncoding = BaseEncoding.base64();
- try {
- byte[] content = Files.toByteArray(pdfFile);
- String encoded = baseEncoding.encode(content); // 将不可打印的字符串转化为可以打印的字符串A-Za-z0-9/+=,pdf不是纯文本文件
- System.out.println("encoded:\n" + encoded);
- System.out.println(Pattern.matches("[A-Za-z0-9/+=]+", encoded));
- // 获得对应的加密字符串,可以解密,可逆的,得到原来的字节
- byte[] decoded = baseEncoding.decode(encoded);
- for(int i = 0; i < content.length; i++){
- assert(content[i] == decoded[i]);
- }
- } catch (IOException e) {
- e.printStackTrace();
- }
二十一、 提醒处理null的类Optional
- Optional<Person> optional = Optional.fromNullable(person1); // 允许参数为null
- System.out.println(optional.isPresent()); // true
- System.out.println(optional.get() == person1); // 如果是person1 == null,get将抛出IllegalStateException, true
- Optional<Person> optional2 = Optional.of(person1); // 不允许参数为null。如果person1 == null, 将抛出NullPointerException
- System.out.println(optional2.isPresent()); // true