DevOps系列文章之 SnakeYAML解析与序列化YAML-编程知识

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 setterspublic 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;}@Overridepublic 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.Testpublic 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;}@Overridepublic 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;}@Overridepublic 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;}@Overridepublic String toString() {return "Contact{" +"type='" + type + '\'' +", number=" + number +'}';}
}

现在，我们来测试下Yaml＃load（）：

@Testpublic voidwhenLoadYAMLDocumentWithTopLevelClass_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 ：

@Testpublic 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：

@Testpublic 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：

@Testpublic 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。

 @Testpublic 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。