Guava工具集使用示例3

Love The Way You Lie 2023-06-05 12:52 41阅读 0赞

### Guava工具集使用示例3 ###

*   *   *  一、异常处理
         *  二、IO读写操作
         *  三、参数校验和Object的toString重写
         *  四、Optional空指针
         *  五、table,二维矩阵的数据结构,可存放比较复杂的结构数据
         *   *  5.1 demo1
             *  5.2 demo2
         *  六、增强集合操作
         *   *  6.1 Multiset

### 一、异常处理 ###

public class ExcepTest {
        // todo Guava异常处理样例
    //    @Test
    //    public void t3() throws IOException,SQLException{
    //        Lists.newArrayList(RandomUtil.randomLong(20))
    //        try {
    //             // todo 可控的异常处理
    //            someMethodThatCouldThrowAnything();
    //        } catch (IKnowWhatToDoWithThisException e) {
    //            handle(e);
    //        } catch (Throwable t) {
                Throwables.throwIfInstanceOf(t, IOException.class);
                Throwables.throwIfInstanceOf(t, SQLException.class);
                throw new RuntimeException(t);  // throw t;{}
    //        }
    //    }
    
        @Test
        public void t1() {
                int a = 2019;
                int b = 0;
            try {
                final int i = a / b;
            }catch (ArithmeticException e){
                throw new ServiceException("分母不能是0啊");
            }
            catch (Throwable t) {
                final String s = Throwables.getStackTraceAsString(t);
                if (s.contains("by zero")) {
                    throw new ServiceException("分母不能是0");
                }
            }
        }
    
        // todo IO流异常处理
        @Test
        public void  test2() {
            // 输入和输出都使用缓冲流
            try {
                FileInputStream in = new FileInputStream("D:\\temp\\a.txt");
                BufferedInputStream inBuffer = new BufferedInputStream(in);
                FileOutputStream out = new FileOutputStream("D:\\temp\\a_copy.txt");
                BufferedOutputStream outBuffer = new BufferedOutputStream(out);
                int len = 0;
                byte[] bs = new byte[1024];
                long begin = System.currentTimeMillis();
                while ((len = inBuffer.read(bs)) != -1) {
                    outBuffer.write(bs, 0, len);
                }
                System.out.println("复制文件所需的时间：" + (System.currentTimeMillis() - begin)); // 平均时间约 200 多毫秒
                inBuffer.close();
                in.close();
                outBuffer.close();
                out.close();
            } catch (FileNotFoundException f) {
                throw new ServiceException("文件未找到!");
            } catch (Throwable t) {
                t.printStackTrace();
            }
        }
    
        @Test
        public void t4() {
            final ArrayList<Integer> list = Lists.newArrayList(1, 2, 3, 3, 3, 5, 46, 4, 7, 8, 7);
            Integer integer = null;
            try {
                integer = list.get(2);
                final int i = integer / 0;
            } catch (Throwable e) {
                Throwables.throwIfInstanceOf(e,NullPointerException.class);
                Throwables.throwIfInstanceOf(e,IndexOutOfBoundsException.class);
            }
            System.out.println(integer);
        }
    
        @Test
        public void t5(){
            String a = "2019-06-16 12:16:49";
            LocalDateTime time = null;
            try {
                time = LocalDateTime.parse(a);
            } catch (DateTimeParseException e){
                throw new ServiceException("时间转换异常");
            }catch (Throwable t) {
                Throwables.throwIfInstanceOf(t, DateTimeParseException.class);
            }
            System.out.println(time);
        }
    
    
    }

### 二、IO读写操作 ###

public class File_test {
    
        // todo Guava IO读写操作
        @Test
        public void t1(){
            String fileName = "d://temp//a.txt";
            String  contents = "ssssssdsd test esdf eesv";
            demoFileWrite(fileName,contents);
        }
    
        @Test
        public void t2() throws IOException {
            String testFilePath = "d://temp//a.txt";
            File testFile = new File(testFilePath);
            List<String> lines = Files.readLines(testFile, Charsets.UTF_8);
            for (String line : lines) {
                System.out.println(line);
            }
        }
    
        public void demoFileWrite(final String fileName, final String contents)
        {
            final File newFile = new File(fileName);
            try
            {
                Files.write(contents.getBytes(), newFile);
            }
            catch (IOException fileIoEx)
            {
                System.err.println(  "ERROR trying to write to file '" + fileName + "' - "
                        + fileIoEx.toString());
            }
        }
    }

### 三、参数校验和Object的toString重写 ###

@Data
    class St1 {
        private String name;
        private Integer age;
        private String city;
    }
    
    @Data
    class St2 {
        private String name;
        private Integer age;
        private String city;
    
        @Override
        public String toString() {
            return "St2{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    ", city='" + city + '\'' +
                    '}';
        }
    }
    
    @Data
    class St3 {
        private String name;
        private Integer age;
        private String city;
    
        // todo guava，重写对象的toString方法，为空时忽略
        @Override
        public String toString() {
            return MoreObjects.toStringHelper(this.getClass())
                    .add("city", city)
                    .add("name", name)
                    .add("age", age)
                    .omitNullValues().toString();
        }
    }
    
    public class TestObjetcs {
        @Test
        public void t1() {
            System.out.println("st1 = " + new St1());
            System.out.println("st2 = " + new St2());
    
            final St3 st3 = new St3();
            st3.setAge(12);
            System.out.println("st3 = " + st3);
        }
    
        @Test
        public void t2() {
            final St3 st3 = new St3();
            st3.setName("zhp");
            st3.setCity("bj");
            st3.setAge(19);
            f1(st3);
        }
    
        // todo guava 参数校验
        public void f1(St3 st3) {
            Preconditions.checkNotNull(st3.getName(), "name may not be null");
            Preconditions.checkArgument(st3.getAge() >= 18 && st3.getAge() < 99, "age must in range (18,99)");
            Preconditions.checkArgument(st3.getCity() != null && st3.getCity().length() < 10, "desc too long, max length is ", 10);
    
        }
    
    }

### 四、Optional空指针 ###

public class Optional_ {
        @Test
        public void t1(){
            // 初始化 List
            List<String> myList = new ArrayList<>();
            myList.add("Geeks");
            myList.add("for");
            myList.add("GeeksClasses");
            myList.add(null);
            myList.add("GeeksforGeeks");
            myList.add("");
            myList.add("Data Structures");
    
            displayValuesUsingJavaNulls(myList); // 基础手写方法判断是否为空代码
            displayValuesUsingGuavaOptional(myList); // 调用 guava Optional封装方法实现
        }
    
        // Method to display values using Java Nulls
        private static void displayValuesUsingJavaNulls(List<String> myList) {
            System.out.println("Displaying values using Java Nulls");
            // For every String in myList
            for (String str : myList) {
                if (str == null || str.isEmpty()) {
                    System.out.println("String : Value is empty or not available");
                }
                else {
                    System.out.println("String : " + str);
                }
            }
            System.out.println();
        }
    
        // Method to display values using Guava Optional
        private static void displayValuesUsingGuavaOptional(List<String> myList) {
            System.out.println("Displaying values using Guava Optional");
    
            for (String str : myList) {
                Optional<String> optionalName = Optional.ofNullable(emptyToNull(str));
                System.out.println("String : " + optionalName.orElse("String : Value is empty or not available"));
            }
        }
    }

### 五、table,二维矩阵的数据结构,可存放比较复杂的结构数据 ###

#### 5.1 demo1 ####

// todo 这是一个二维表的数据结构，一个二维矩阵
    // Table是Guava提供的一个接口 Interface Table(R,C,V)，由rowKey(行)+columnKey(列)+value组成
    // 适用于多个健做索引的场景
    public class Table_ {
        @Test
        public void t1(){
    
           Table<String, String, String> studentTable = HashBasedTable.create();
            studentTable.put("CSE", "5", "Dhiman");
            studentTable.put("CSE", "7", "Shubham");
            studentTable.put("CSE", "9", "Abhishek");
            studentTable.put("CSE", "12", "Sahil");
    
            studentTable.put("ECE", "15", "Ram");
            studentTable.put("ECE", "12", "Lube");
            studentTable.put("ECE", "18", "Anmol");
            studentTable.put("ECE", "20", "Akhil");
            studentTable.put("ECE", "25", "Amrit");
    
            Map<String, String> eceMap = studentTable.row("ECE");
            System.out.println("List of ECE students : ");
    
            for (Map.Entry<String, String> student : eceMap.entrySet()) {
                System.out.println("Student Roll No : " + student.getKey() + ", Student Name : " + student.getValue());
            }
    
            System.out.println();
    
            Map<String, String> stuMap = studentTable.column("12");
            for (Map.Entry<String, String> student : stuMap.entrySet()) {
                System.out.println("Student Roll No : " + student.getKey() + ", Student Name : " + student.getValue());
            }
        }
    
    
    }

#### 5.2 demo2 ####

### 六、增强集合操作 ###

#### 6.1 Multiset ####

public class Multiset_test {
    
        // todo Multiset对象不是set,是一个Collection,它本质上是一个Set加一个元素计数器。
        @Test
        public void t1(){
            Multiset multiset = HashMultiset.create();
            String sentences = "this is a story, there is a good girl in the story.";
            Iterable<String> words = Splitter.onPattern("[^a-z]{1,}").omitEmptyStrings().trimResults().split(sentences);
            for (String word : words) {
                multiset.add(word);
            }
            final Set set = multiset.elementSet();
            final Set set1 = multiset.entrySet();
            for (Object element : multiset.elementSet()) {
                System.out.println((String)element + ":" + multiset.count(element));
            }
        }
    
        // todo 存放POJO时，可重写POJO的equals方法，除重或者统计使用
        @Test
        public void t2(){
            Multiset multiset = HashMultiset.create();
    
            List<A> lists = Lists.newArrayList();
            for (int i = 0; i < 11; i++) {
                final A a = new A().setId(i).setName("test" + i);
                lists.add(a);
            }
    
            lists.add(new A().setId(2).setName("test2"));
            lists.add(new A().setId(2).setName("test222"));
            for (A a: lists) {
                multiset.add(a);
            }
    
            final Set set1 = multiset.elementSet();
            final Set set2 = multiset.entrySet();
    
            for (Object element : multiset.elementSet()) {
                System.out.println((A)element + ":" + multiset.count(element));
            }
        }
    
    }
    
    @Data
    @Accessors(chain = true)
    class A{
        private Integer id;
        private String name;
    
        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            A a = (A) o;
            return Objects.equals(id, a.id);
        }
    
        @Override
        public int hashCode() {
            return Objects.hash(id);
        }
    }