使用Jackson（JSON）序列化 - 获取“未找到序列化程序”？ [英] Serializing with Jackson (JSON) - getting "No serializer found"?

问题描述

我尝试使用Jackson序列化一个非常简单的对象时遇到异常。错误：

I get the an exception when trying to serialize a very simple object using Jackson. The error:

org.codehaus.jackson.map.JsonMappingException：找不到
类MyPackage.TestA的序列化程序且没有属性发现
创建BeanSerializer（为了避免异常，禁用
SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS））

org.codehaus.jackson.map.JsonMappingException: No serializer found for class MyPackage.TestA and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) )

下面是要序列化的简单类和代码。

Below is the simple class and code to serialize.

有谁可以告诉我为什么会收到此错误？

Can anyone tell my why I get this error?

public class TestA {
    String SomeString = "asd";
}

TestA testA = new TestA();
ObjectMapper om = new ObjectMapper();
try {
    String testAString = om.writeValueAsString(testA); // error here!

    TestA newTestA = om.readValue(testAString, TestA.class);
} catch (JsonGenerationException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (JsonMappingException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

推荐答案

如前所述，默认 ObjectMapper 实例的配置是仅访问属于公共字段或具有公共getter / setter的属性。更改类定义以使字段公开或提供公共getter / setter的替代方法是指定（对于基础 VisibilityChecker ）不同的属性可见性规则。 Jackson 1.9为此提供了 ObjectMapper.setVisibility（）便捷方法。对于原始问题中的示例，我可能将其配置为

As already described, the default configuration of an ObjectMapper instance is to only access properties that are public fields or have public getters/setters. An alternative to changing the class definition to make a field public or to provide a public getter/setter is to specify (to the underlying VisibilityChecker) a different property visibility rule. Jackson 1.9 provides the ObjectMapper.setVisibility() convenience method for doing so. For the example in the original question, I'd likely configure this as

myObjectMapper.setVisibility(JsonMethod.FIELD, Visibility.ANY);

有关相关配置选项的更多信息和详细信息，建议您查看 上的JavaDocs> ObjectMapper.setVisibility（） 。

For more information and details on related configuration options, I recommend reviewing the JavaDocs on ObjectMapper.setVisibility().

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