codehaus jackson ObjectReader 的反序列化功能

Question

如何为对象 reader 应用反序列化功能 (FAIL_ON_UNKNOWN_PROPERTIES)？我知道如何为 objectMapper 完成它，但是如何在 codehaus jackson 中的 objectReader 上完成它？

Answer 1

自从某些版本 Jackson 引入了 ObjectReader#with 方法来实现你想要的。也许迁移到更高版本会更容易。

但是，如果您不能使用更高版本，您可以使用ObjectMapper#configure method. After you set this feature to true you can create ObjectReader from ObjectMapper with reader方法设置此功能。

正如您在 ObjectReader 的文档中所见，您无法在创建后更改其功能。但是读者不共享映射器状态。因此，如果您需要从一个映射器创建多个读取器，并且只有少数读取器需要此选项，您可以在 ObjectMapper 中仅为它们设置功能。您可以像这样获取该功能的当前状态

boolean enabled = mapper.getDeserializationConfig().isEnabled(feature);

改变状态然后return恢复到原来的状态。请参阅示例中的 createReader(Class<T> clazz, DeserializationConfig.Feature feature) 方法。

这是我们要反序列化的 POJO

class ExamplePojo {
    private int a1;
    private String b1;

    public ExamplePojo() {

    }

    public ExamplePojo(int a1, String b1) {
        this.a1 = a1;
        this.b1 = b1;
    }

    public int getA1() {
        return a1;
    }

    public void setA1(int a1) {
        this.a1 = a1;
    }

    public String getB1() {
        return b1;
    }

    public void setB1(String b1) {
        this.b1 = b1;
    }
}

这是例子

import org.codehaus.jackson.map.DeserializationConfig;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.ObjectReader;
import org.codehaus.jackson.map.exc.UnrecognizedPropertyException;

public class JacksonExample {

    static ObjectMapper mapper = new ObjectMapper();

    public static <T> ObjectReader createReader(Class<T> clazz, DeserializationConfig.Feature feature) {
        boolean enabled = mapper.getDeserializationConfig().isEnabled(feature);

        mapper.configure(feature, true);
        ObjectReader reader = mapper.reader(clazz);
        mapper.configure(feature, enabled);

        return reader;
    }

    public static <T> ObjectReader createReader(Class<T> clazz) {
        return mapper.reader(clazz);
    }

    public static void main(String[] args) throws Exception {

        // by default turn off this feature
        mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);

        // Should fail
        ObjectReader r1 = createReader(ExamplePojo.class, DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES);
        try {
            ExamplePojo ex = r1.readValue("{\"a1\":1,\"b1\":\"Hello!\",\"c1\":1}");
            System.out.println(ex.getA1() + " " + ex.getB1());
        } catch (UnrecognizedPropertyException ex) {
            System.out.println(ex.getMessage());
        }

        // Should be ok
        ObjectReader r2 = createReader(ExamplePojo.class);
        try {
            ExamplePojo ex = r2.readValue("{\"a1\":2,\"b1\":\"Hello!\",\"c1\":2}");
            System.out.println(ex.getA1() + " " + ex.getB1());
        } catch (UnrecognizedPropertyException ex) {
            System.out.println(ex.getMessage());
        }

        // Should fail
        try {
            ExamplePojo ex = r1.readValue("{\"a1\":3,\"b1\":\"Hello!\",\"c1\":3}");
            System.out.println(ex.getA1() + " " + ex.getB1());
        } catch (UnrecognizedPropertyException ex) {
            System.out.println(ex.getMessage());
        }

        // Should be ok
        try {
            ExamplePojo ex = r2.readValue("{\"a1\":4,\"b1\":\"Hello!\",\"c1\":4}");
            System.out.println(ex.getA1() + " " + ex.getB1());
        } catch (UnrecognizedPropertyException ex) {
            System.out.println(ex.getMessage());
        }
    }
}

以及此示例的输出

Unrecognized field "c1" (Class ExamplePojo), not marked as ignorable at [Source: java.io.StringReader@7c30a502; line: 1, column: 29] (through reference chain: ExamplePojo["c1"])

2 Hello!

Unrecognized field "c1" (Class ExamplePojo), not marked as ignorable at [Source: java.io.StringReader@49e4cb85; line: 1, column: 29] (through reference chain: ExamplePojo["c1"])

4 Hello!

codehaus jackson ObjectReader 的反序列化功能

Deserialization feature on codehaus jackson ObjectReader

java

jackson

deserialization