[英]ObjectMapper - How to convert a Map to POJO
我是Java的新手,正在尝试学习objectmapper。 我正在使用它将地图转换为pojo。 映射中的键是字符串,所有值都是字符串值,但我要转换为映射的键值除外。 请通过下面的示例代码获得更清晰的图片。
POJO类别:
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import javax.annotation.Nonnull;
import java.util.Map;
public class POJOClass {
private String string1;
private Map<String, String> map1;
@JsonCreator
public POJOClass(@Nonnull @JsonProperty(value="String1", required = true) String string1,
@Nonnull @JsonProperty(value = "Map1", required = true) Map<String, String> map1) {
this.string1 = string1;
this.map1 = map1;
}
@Nonnull
public String getString1() {
return string1;
}
@Nonnull
public Map<String, String> getMap1() {
return map1;
}
}
测试代码:
@Test
public void testPOJOClass() {
Map<String, String> map = new HashMap<>();
map.put("String1", "string");
map.put("Map1", "{\"key1\" : \"value1\", \"key2\":\"value2\", \"key3\" : null }");
ObjectMapper mapper = new ObjectMapper();
POJOClass pojoClass = mapper.convertValue(map, POJOClass.class);
}
例外:
java.lang.IllegalArgumentException: Can not instantiate value of type [map type; class java.util.LinkedHashMap, [simple type, class java.lang.String] -> [simple type, class java.lang.String]] from String value ('{"key1" : "value1", "key2":"value2", "key3" : null }'); no single-String constructor/factory method
at [Source: N/A; line: -1, column: -1]
at com.fasterxml.jackson.databind.ObjectMapper._convert(ObjectMapper.java:3286)
at com.fasterxml.jackson.databind.ObjectMapper.convertValue(ObjectMapper.java:3212)
变式选项尝试:
我知道我也可以将map1字段保留为String,以后再使用对象映射器的另一个实例将其转换为map,但是我想避免使用它。 有什么方法可以直接将测试代码中的字符串直接转换为提到的Pojo。
我什至尝试将map1的类型从Map更改为Map,但即使这样也不起作用。
public class CustomerDeserializer extends JsonDeserializer<Map<String, String>> {
@Override
public Map<String, String> deserialize(final JsonParser p, final DeserializationContext ctxt) throws IOException, JsonProcessingException {
final ObjectMapper mapper = (ObjectMapper) p.getCodec();
return mapper.readValue(p.getText(), new TypeReference<Map<String, String>>() {
});
}
}
您可以编写客户反序列化器,在构造函数@JsonDeserialize(using = CustomerDeserializer.class) @JsonProperty(value = "Map1", required = true) Map<String, String> map1) {
map1
参数上注释JsonDeserialize @JsonDeserialize(using = CustomerDeserializer.class) @JsonProperty(value = "Map1", required = true) Map<String, String> map1) {
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