JAVA使用SnakeYAML解析与序列化YAML

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

<dependency> <groupId>org.yaml</groupId> <artifactId>snakeyaml</artifactId> <version>1.25</version> </dependency> 3.入口点

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:

firstName: "John" lastName: "Doe" age: 20 4.1。基本用法

现在,我们将使用Yaml类来解析上述YAML文档:

Yaml yaml = new Yaml(); InputStream inputStream = this.getClass() .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:

{firstName=John, lastName=Doe, age=20}

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。

4.2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:

public class Customer { private String firstName; private String lastName; private int age; // getters and setters }

现在我么来加载:

Yaml yaml = new Yaml(); InputStream inputStream = this.getClass() .getClassLoader() .getResourceAsStream("customer.yaml"); Customer customer = yaml.load(inputStream);

还有一种方法是使用Constructor:

Yaml yaml = new Yaml(new Constructor(Customer.class)); 4.3。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:

@Test public void whenLoadYAML_thenLoadCorrectImplicitTypes() { Yaml yaml = new Yaml(); Map<Object, Object> document = yaml.load("3.0: 2018-07-22"); assertNotNull(document); assertEquals(1, document.size()); assertTrue(document.containsKey(3.0d)); } 4.4 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:

public class Customer { private String firstName; private String lastName; private int age; private List<Contact> contactDetails; private Address homeAddress; // getters and setters } public class Contact { private String type; private int number; // getters and setters } public class Address { private String line; private String city; private String state; private Integer zip; // getters and setters }

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("yaml/customer_with_contact_details_and_address.yaml"); Customer customer = yaml.load(inputStream); 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()); } 4.5。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,以以便可以正确解析。

让我们假设一个 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 

Constructor constructor = new Constructor(Customer.class); TypeDescription customTypeDescription = new TypeDescription(Customer.class); customTypeDescription.addPropertyParameters("contactDetails", Contact.class); constructor.addTypeDescription(customTypeDescription); Yaml yaml = new Yaml(constructor); 4.6。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

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