Guava工具集使用示例3

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);
    }
}