DevOps系列文章之 SnakeYAML解析与序列化YAML

1、简述

如何使用SnakeYAML库将
YAML文档转换为Java对象，以及JAVA对象如何序列化为YAML文档。

在DevOps平台系统中是基础的能力支持，不管是spring boot 的配置还是K8S 资源清单yaml

2、项目设置

要在项目中使用SnakeYAML，需要添加Maven依赖项（可在此处找到最新版本）

<dependency>
    <groupId>org.yaml</groupId>
    <artifactId>snakeyaml</artifactId>
    <version>1.25</version>
</dependency>

3、入口点

该YAML类是API的入口点：

Yaml yaml = new Yaml()

由于实现不是线程安全的，因此不同的线程必须具有自己的Yaml实例。

4、加载YAML文档

SnakeYAML支持从String或InputStream加载文档，我们从定义一个简单的YAML文档开始，然后将文件命名为customer.yaml：

基本用法

现在，我们将使用Yaml类来解析上述YAML文档：

public class YamlTest {
    public static void main(String[] args) {
        Yaml yaml = new Yaml();
        InputStream inputStream = YamlTest.class
                .getClassLoader()
                .getResourceAsStream("customer.yaml");
        Map<String, Object> obj = yaml.load(inputStream);
        System.out.println(obj);

    }
}

上面的代码生成以下输出：

默认情况下，load（）方法返回一个Map对象。查询Map对象时，我们需要事先知道属性键的名称，否则容易出错。更好的办法是自定义类型。

自定义类型解析

SnakeYAML提供了一种将文档解析为自定义类型的方法

让我们定义一个Customer类，然后尝试再次加载该文档：

package com.devops.autocicdstore.yaml;

/**
 * @Author 虎哥
 * @Description //TODO
 * |要带着问题去学习,多猜想多验证|
 **/

public class Customer {

    private String firstName;
    private String lastName;
    private int age;

    // getters and setters

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Customer{" +
                "firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", age=" + age +
                '}';
    }
}

现在我么来加载：

        Yaml yaml = new Yaml(new Constructor(Customer.class));
        InputStream inputStream = YamlTest.class
                .getClassLoader()
                .getResourceAsStream("customer.yaml");
        Customer customer = yaml.load(inputStream);
        System.out.println(customer);

隐式类型

如果没有为给定属性定义类型，则库会自动将值转换为隐式type。

例如：

1.0 -> Float
42 -> Integer
2009-03-30 -> Date

让我们使用一个TestCase来测试这种隐式类型转换：

@org.junit.Test
    public void whenLoadYAML_thenLoadCorrectImplicitTypes() {
        Yaml yaml = new Yaml();
        Map<Object, Object> document = yaml.load("3.0: 2018-07-22");
        System.out.println(document);
        assertNotNull(document);
        assertEquals(1, document.size());
        assertTrue(document.containsKey(3.0d));
    }

嵌套对象

SnakeYAML 支持嵌套的复杂类型。

让我们向“ customer.yaml”添加“ 联系方式” 和“ 地址” 详细信息，并将新文件另存为customer_with_contact_details_and_address.yaml.。

现在，我们将分析新的YAML文档

firstName: "John"
lastName: "Doe"
age: 31
contactDetails:
   - type: "mobile"
     number: 123456789
   - type: "landline"
     number: 456786868
homeAddress:
   line: "Xyz, DEF Street"
   city: "City Y"
   state: "State Y"
   zip: 345657

我们来更新java类：

package com.devops.autocicdstore.yaml;

import java.util.List;

/**
 * @Author 虎哥
 * @Description //TODO
 * |要带着问题去学习,多猜想多验证|
 **/

public class Customer {

    private String firstName;
    private String lastName;
    private int age;
    private List<Contact> contactDetails;
    private Address homeAddress;

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public List<Contact> getContactDetails() {
        return contactDetails;
    }

    public void setContactDetails(List<Contact> contactDetails) {
        this.contactDetails = contactDetails;
    }

    public Address getHomeAddress() {
        return homeAddress;
    }

    public void setHomeAddress(Address homeAddress) {
        this.homeAddress = homeAddress;
    }

    @Override
    public String toString() {
        return "Customer{" +
                "firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", age=" + age +
                ", contactDetails=" + contactDetails +
                ", homeAddress=" + homeAddress +
                '}';
    }
}

package com.devops.autocicdstore.yaml;

/**
 * @Author 虎哥
 * @Description //TODO
 * |要带着问题去学习,多猜想多验证|
 **/
public class Address {
    private String line;
    private String city;
    private String state;
    private Integer zip;

    public String getLine() {
        return line;
    }

    public void setLine(String line) {
        this.line = line;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    public Integer getZip() {
        return zip;
    }

    public void setZip(Integer zip) {
        this.zip = zip;
    }

    @Override
    public String toString() {
        return "Address{" +
                "line='" + line + '\'' +
                ", city='" + city + '\'' +
                ", state='" + state + '\'' +
                ", zip=" + zip +
                '}';
    }
}

package com.devops.autocicdstore.yaml;

/**
 * @Author 虎哥
 * @Description //TODO
 * |要带着问题去学习,多猜想多验证|
 **/
public class Contact {
    private String type;
    private int number;

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public int getNumber() {
        return number;
    }

    public void setNumber(int number) {
        this.number = number;
    }

    @Override
    public String toString() {
        return "Contact{" +
                "type='" + type + '\'' +
                ", number=" + number +
                '}';
    }
}

现在，我们来测试下Yaml＃load（）：

@Test
    public void
    whenLoadYAMLDocumentWithTopLevelClass_thenLoadCorrectJavaObjectWithNestedObjects() {

        Yaml yaml = new Yaml(new Constructor(Customer.class));
        InputStream inputStream = this.getClass()
                .getClassLoader()
                .getResourceAsStream("customer_with_contact_details_and_address.yaml");
        Customer customer = yaml.load(inputStream);
        System.out.println(customer);
        assertNotNull(customer);
        assertEquals("John", customer.getFirstName());
        assertEquals("Doe", customer.getLastName());
        assertEquals(31, customer.getAge());
        assertNotNull(customer.getContactDetails());
        assertEquals(2, customer.getContactDetails().size());

        assertEquals("mobile", customer.getContactDetails()
                .get(0)
                .getType());
        assertEquals(123456789, customer.getContactDetails()
                .get(0)
                .getNumber());
        assertEquals("landline", customer.getContactDetails()
                .get(1)
                .getType());
        assertEquals(456786868, customer.getContactDetails()
                .get(1)
                .getNumber());
        assertNotNull(customer.getHomeAddress());
        assertEquals("Xyz, DEF Street", customer.getHomeAddress()
                .getLine());
    }

类型安全的集合

当给定Java类的一个或多个属性是泛型集合类时，需要通过TypeDescription来指定泛型类型，以便可以正确解析。

让我们假设一个Customer拥有多个Contact：

firstName: "John"
lastName: "Doe"
age: 31
contactDetails:
   - { type: "mobile", number: 123456789}
   - { type: "landline", number: 123456789}

为了能正确解析，我们可以在顶级类上为给定属性指定TypeDescription ：

@Test
    public void test1(){
        Constructor constructor = new Constructor(Customer.class);
        TypeDescription customTypeDescription = new TypeDescription(Customer.class);
        customTypeDescription.addPropertyParameters("contactDetails", Contact.class);
        constructor.addTypeDescription(customTypeDescription);
        Yaml yaml = new Yaml(new Constructor(Customer.class));
        InputStream inputStream = this.getClass()
                .getClassLoader()
                .getResourceAsStream("customer_with_contact_details_and_address.yaml");
        Customer customer = yaml.load(inputStream);
        System.out.println(customer);
    }

载入多个文件

在某些情况下，单个文件中可能有多个YAML文档，而我们想解析所有文档。所述YAML类提供了一个LOADALL（）方法来完成这种类型的解析。

假设下面的内容在一个文件中：

---
firstName: "John"
lastName: "Doe"
age: 20
---
firstName: "Jack"
lastName: "Jones"
age: 25

我们可以使用loadAll（）方法解析以上内容，如以下代码示例所示：


    @Test
    public void whenLoadMultipleYAMLDocuments_thenLoadCorrectJavaObjects() {
        Yaml yaml = new Yaml(new Constructor(Customer.class));
        InputStream inputStream = this.getClass()
                .getClassLoader()
                .getResourceAsStream("customers.yaml");

        int count = 0;
        for (Object object : yaml.loadAll(inputStream)) {
            count++;
            assertTrue(object instanceof Customer);
            System.out.println(object);
        }
        assertEquals(2,count);
    }

5、生成YAML文件

SnakeYAML 支持将java对象序列化为yml。

基本用法

我们将从一个将Map <String，Object>的实例转储到YAML文档（String）的简单示例开始：

@Test
    public void whenDumpMap_thenGenerateCorrectYAML() {
        Map<String, Object> data = new LinkedHashMap<String, Object>();
        data.put("name", "Silenthand Olleander");
        data.put("race", "Human");
        data.put("traits", new String[] { "ONE_HAND", "ONE_EYE" });
        Yaml yaml = new Yaml();
        StringWriter writer = new StringWriter();
        yaml.dump(data, writer);
        String expectedYaml = "name: Silenthand Olleander\nrace: Human\ntraits: [ONE_HAND, ONE_EYE]\n";
        System.out.println(writer);
        assertEquals(expectedYaml, writer.toString());
    }

上面的代码产生以下输出（请注意，使用LinkedHashMap的实例将保留输出数据的顺序）：

自定义Java对象

我们还可以选择将自定义Java类型转储到输出流中。

 @Test
    public void whenDumpACustomType_thenGenerateCorrectYAML() {
        Customer customer = new Customer();
        customer.setAge(45);
        customer.setFirstName("Greg");
        customer.setLastName("McDowell");
        Yaml yaml = new Yaml();
        StringWriter writer = new StringWriter();
        yaml.dump(customer, writer);
        String expectedYaml = "!!com.devops.autocicdstore.yaml.Customer {age: 45, contactDetails: null, firstName: Greg,\n  homeAddress: null, lastName: McDowell}\n";
        System.out.println(writer);
        assertEquals(expectedYaml, writer.toString());
    }

生成内容会包含!!com.devops.autocicdstore.yaml.Customer，为了避免在输出文件中使用标签名，我们可以使用库提供的 dumpAs（）方法。

因此，在上面的代码中，我们可以进行以下调整以删除标记：

yaml.dumpAs(customer, Tag.MAP, null);

String ccustomerStr = yaml.dumpAs(customer, Tag.MAP, null);

System.out.println(ccustomerStr);

本文说明了SnakeYAML库解析和序列化YAML文档。