java - 从 Yaml 文件加载 Java Builder 对象

Question

我使用构建器模式创建了一个 Bean 类，但在从 yaml 文件创建对象时遇到了问题。

这是一个示例类(实际类很大，如果您想用示例回答，这只是一个摘录):

public class ClientBuilder {

    private final String firstName;
    private final String lastName;
    private final String displayName;

    private ClientBuilder(Builder builder) { 
        firstName   = builder.firstName; 
        lastName    = builder.lastName; 
        displayName = builder.displayName;
    }

    public static class Builder {

        private final String displayName; // Mandatory Attribute

        public Builder( String displayName ) {
            this.displayName = displayName;
        }

        private String firstName;
        private String lastName;

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

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

        public ClientBuilder build() {
            return new ClientBuilder(this);
        }
    }

    @Override
    public String toString() {
        StringBuffer sbf = new StringBuffer();
        sbf.append("New Company Object: \n");
        sbf.append("firstName   : " +  this.firstName   + "\n");
        sbf.append("lastName    : " +  this.lastName    + "\n");
        sbf.append("displayName : " +  this.displayName + "\n");
        return sbf.toString();
    }
}

我正在使用 snakeyaml 加载文件，但任何 yaml api 都可以。由于 displayName 是强制参数，我想在创建实例时传递该值。可以在创建对象时传递其他参数，但我希望可以选择通过 yaml 文件加载它们。

如果我使用 java bean，我可以加载 yaml 文件。有没有办法实例化构建器对象？

我试过:

InputStream input = new FileInputStream(new File("src/main/resources/client.yaml"));
Yaml yaml = new Yaml();
Builder builder = new Builder("Display Name");
builder = (Builder) yaml.loadAs(input, ClientBuilder.Builder.class);
ClientBuilder client = builder.build();
System.out.println(client.toString());

但我得到以下错误:

Exception in thread "main" Can't construct a java object for tag:yaml.org,2002:com.xxx.xxx.xxx.ClientBuilder$Builder; exception=java.lang.NoSuchMethodException: com.xxx.xxx.xxx.ClientBuilder$Builder.<init>()
 in 'reader', line 2, column 1:
    firstName: "Jaypal"

Answer 1

SnakeYaml 是一个非常强大的库，它支持基于构造函数注入(inject)创建实例。

/**
 * create JavaBean
 */
public void testGetBeanAssumeClass() {
    String data = "--- !!org.yaml.snakeyaml.constructor.Person\nfirstName: Andrey\nage: 99";
    Object obj = construct(data);
    assertNotNull(obj);
    assertTrue("Unexpected: " + obj.getClass().toString(), obj instanceof Person);
    Person person = (Person) obj;
    assertEquals("Andrey", person.getFirstName());
    assertNull(person.getLastName());
    assertEquals(99, person.getAge().intValue());
}

/**
 * create instance using constructor arguments
 */
public void testGetConstructorBean() {
    String data = "--- !!org.yaml.snakeyaml.constructor.Person [ Andrey, Somov, 99 ]";
    Object obj = construct(data);
    assertNotNull(obj);
    assertTrue(obj.getClass().toString(), obj instanceof Person);
    Person person = (Person) obj;
    assertEquals("Andrey", person.getFirstName());
    assertEquals("Somov", person.getLastName());
    assertEquals(99, person.getAge().intValue());
}

Junit code sample可以在这里查看。所以你的代码仍然有效。您可能需要以适当的格式更改 yaml 内容。完成后，一切就绪。