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Building a Custom Jackson Deserializer
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package com.robinhowlett.blog; | |
import java.io.IOException; | |
import com.fasterxml.jackson.core.JsonParser; | |
import com.fasterxml.jackson.core.JsonProcessingException; | |
import com.fasterxml.jackson.core.JsonToken; | |
import com.fasterxml.jackson.databind.DeserializationContext; | |
import com.fasterxml.jackson.databind.JsonDeserializer; | |
/** | |
* Deserializer that case-insensitively deserializes | |
* "yes", "no", and null JSON field values to | |
* true, false, and false respectively | |
* | |
* @author robin | |
* | |
*/ | |
public class YesNoBooleanDeserializer extends JsonDeserializer<Boolean> { | |
protected static final String NO = "no"; | |
protected static final String YES = "yes"; | |
/* (non-Javadoc) | |
* @see com.fasterxml.jackson.databind.JsonDeserializer#deserialize(com.fasterxml.jackson.core.JsonParser, com.fasterxml.jackson.databind.DeserializationContext) | |
*/ | |
@Override | |
public Boolean deserialize(JsonParser jp, DeserializationContext ctxt) | |
throws IOException, JsonProcessingException { | |
JsonToken currentToken = jp.getCurrentToken(); | |
if (currentToken.equals(JsonToken.VALUE_STRING)) { | |
String text = jp.getText().trim(); | |
if (YES.equalsIgnoreCase(text)) { | |
return Boolean.TRUE; | |
} else if (NO.equalsIgnoreCase(text)) { | |
return Boolean.FALSE; | |
} | |
throw ctxt.weirdStringException(text, Boolean.class, | |
"Only \"" + YES + "\" or \"" + NO + "\" values supported"); | |
} else if (currentToken.equals(JsonToken.VALUE_NULL)) { | |
return getNullValue(); | |
} | |
throw ctxt.mappingException(Boolean.class); | |
} | |
@Override | |
public Boolean getNullValue() { | |
return Boolean.FALSE; | |
} | |
} |
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package com.robinhowlett.blog; | |
import static org.junit.Assert.assertFalse; | |
import static org.junit.Assert.assertTrue; | |
import java.io.IOException; | |
import org.junit.After; | |
import org.junit.Before; | |
import org.junit.Test; | |
import com.fasterxml.jackson.core.JsonParseException; | |
import com.fasterxml.jackson.core.JsonProcessingException; | |
import com.fasterxml.jackson.databind.JsonMappingException; | |
import com.fasterxml.jackson.databind.ObjectMapper; | |
import com.fasterxml.jackson.databind.annotation.JsonDeserialize; | |
/** | |
* Test that "yes", "no" and null values that are deserialized | |
* with {@link YesNoBooleanDeserializer} return true, false, and | |
* false respectively | |
* | |
* @author robin | |
* | |
*/ | |
public class YesNoBooleanDeserializerTest { | |
private ObjectMapper mapper; | |
/** | |
* @throws java.lang.Exception | |
*/ | |
@Before | |
public void setUp() throws Exception { | |
mapper = new ObjectMapper(); | |
} | |
/** | |
* @throws java.lang.Exception | |
*/ | |
@After | |
public void tearDown() throws Exception { | |
mapper = null; | |
} | |
@Test | |
public void yes() throws JsonParseException, IOException { | |
String yes = "\"" + YesNoBooleanDeserializer.YES + "\""; | |
Boolean result = deserialize(yes); | |
assertTrue(result); | |
result = deserialize(yes.toUpperCase()); | |
assertTrue(result); | |
} | |
@Test | |
public void no() throws JsonParseException, IOException { | |
String no = "\"" + YesNoBooleanDeserializer.NO + "\""; | |
Boolean result = deserialize(no); | |
assertFalse(result); | |
result = deserialize(no.toUpperCase()); | |
assertFalse(result); | |
} | |
@Test | |
public void nullValue() throws JsonParseException, IOException { | |
// null values must deserialize as Boolean.FALSE to support primitives | |
Boolean result = deserialize(null); | |
assertFalse(result); | |
} | |
@Test(expected=JsonMappingException.class) | |
public void neitherYesOrNo() throws JsonParseException, IOException { | |
deserialize("\"never\""); | |
} | |
private Boolean deserialize(String yesOrNo) throws IOException, JsonParseException, | |
JsonProcessingException { | |
TestObject testObject = mapper.readValue("{\"exists\":" + yesOrNo + "}", TestObject.class); | |
return testObject.getExists(); | |
} | |
private static class TestObject { | |
@JsonDeserialize(using = YesNoBooleanDeserializer.class) | |
private final Boolean exists = null; | |
public Boolean getExists() { | |
return exists; | |
} | |
} | |
} |
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Thank you, it works