How do I marshall nested key,value pairs into JSON with Camel and Jackson library?
Your structure is a more than a map. It's two maps that are serialised differently. One way to represent this is:
public class Whatever{
Map<String,String> keyvalues;
Map<String,String> visibility;
}
What you'll end up with is this, which although represents the data is far from ideal:
{
"keyvalues" : { "key1": "5", "key2": "10", "key3": "17"},
"visibility" : { "key1": "a&b&!c", "key2": "a&b", "_default": "a" }
}
To get what you want, use @JsonAnyGetter. Something like this (it could be made much easier to use):
public class Whatever{
Map<String,String> keyvalues = new TreeMap<String,String>();
@JsonProperty
Map<String,String> visibility = new TreeMap<String,String>();
@JsonAnyGetter
public Map<String, String> getKeyvalues() {
return keyvalues;
}
}
which produces:
{"visibility":{"key1":"a&b&!c","key2":"a&b"},"key1":"5","key2":"10"}
I've been battling this today and your question inspired me to make it bloody work :D The annotations are here: https://github.com/FasterXML/jackson-annotations/wiki/Jackson-Annotations
See JUnit test here: https://gist.github.com/TomDemeranville/7009250
erj2code
Updated on June 13, 2022Comments
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erj2code almost 2 years
I have a Java project that currently returns a map to Camel without any nested key,value pairs, and the Jackson library marshalls it just fine into JSON using the Jackson library.
For example if I put the following two key,values into a demoMap:
Map<String,String> demoMap = new TreeMap<String,String> demoMap.put("key1","5"); demoMap.put("key2","10");
I get the following JSON:
{"key1":"5","key2":"10"}
However, now some of my key,value entries will have an optional visibility that I need to put as a nested key value in my map. Any key,values that don't have an optional visibility will use the default. So, for example if I specify visibilities for key1, and key2, but not key3 I want to get JSON out that looks like this:
{"key1":"5", "key2":"10", "key3":"17", "visibility" : { "key1": "a&b&!c", "key2": "a&b", "_default": "a" } }
How can I get Camel to marshall a Java object with nested key,value pairs? I'm a visual learner, so a simple example would be helpful.
I tried changing my Map to have a value as an object i.e.,:
Map<String,Object> demoMap = new TreeMap<String,Object>
and then tried adding nested key,values for some keys with an ArrayList using http://examples.javacodegeeks.com/core-java/json/jackson/convert-java-map-to-from-json-using-jackson-example/ for reference, but realized that this just gives me a bunch of nested values under a key, not a bunch of nested key,value pairs.
Even when I tried it for grins, I got an error from the Camel processor with a java.lang.ClassCastException stating java.util.ArrayList cannot be cast to java.lang.String
And similarly when I tried to nest a Map inside my demoMap I got this ClassCastException:
3244 [hello.world.request.timer] ERROR org.apache.camel.processor.DefaultErrorHandler - Failed delivery for exchangeId: e6518e39-89b7-435e-96d9-ce26811ac67e. Exhausted after delivery attempt: 1 caught: java.lang.ClassCastException: java.util.HashMap cannot be cast to java.lang.String
So I know how NOT to do it. :-/
I re-read the Camel JSON documentation at http://camel.apache.org/json.html but as of this writing it doesn't specify an example with nested key,value pairs.
UPDATE: Based on feedback from Tom I created two Maps i.e.,
Map<String,String> keyvalues = new TreeMap<String,String>(); Map<String,String> visibility = new TreeMap<String,String>();
Here is my class which I call SensorGenerator that loads a properties file into a Map:
package sample; import java.util.Map; import java.util.Properties; import java.util.TreeMap; import org.codehaus.jackson.annotate.JsonAnyGetter; import org.codehaus.jackson.annotate.JsonProperty; public class SensorGenerator { private Properties sourceProperties; // create a map of sensor keyvalues, and a map of sensor visibility Map<String,String> keyvalues = new TreeMap<String,String>(); @JsonProperty Map<String,String> visibility = new TreeMap<String,String>(); @JsonAnyGetter public Map<String, String> getKeyvalues() { for (Object key : sourceProperties.keySet()) { // Separate out each of the field:datatype:visibility tuples as an entry in the // values array String[] values = sourceProperties.getProperty((String) key).split( ","); // split the key between 'sensor' and the 'number' Ex: sensor1 -> sensor,1 String[] keyArray = key.toString().split("(?<=([a-zA-Z]++))"); String keyNumber = keyArray[1]; // grab the number to append for each sensor // define string buffer that appends sensor number for each sensor's // keys. Ex: sensor1 would have s1make, s1makeDataType, etc. StringBuffer sensorNumberStringBuffer = new StringBuffer(); sensorNumberStringBuffer.append("s"); sensorNumberStringBuffer.append(keyNumber); // make, its data type, and visibility (with s# prefix) StringBuffer makeStringBuffer = new StringBuffer(); makeStringBuffer.append(sensorNumberStringBuffer); makeStringBuffer.append("make"); StringBuffer makeDataTypeStringBuffer = new StringBuffer(); makeDataTypeStringBuffer.append(sensorNumberStringBuffer); makeDataTypeStringBuffer.append("makeDataType"); StringBuffer makeVizStringBuffer = new StringBuffer(); makeVizStringBuffer.append(sensorNumberStringBuffer); makeVizStringBuffer.append("makeViz"); // model, its data type, and visibility (with s# prefix) StringBuffer modelStringBuffer = new StringBuffer(); modelStringBuffer.append(sensorNumberStringBuffer); modelStringBuffer.append("model"); StringBuffer modelDataTypeStringBuffer = new StringBuffer(); modelDataTypeStringBuffer.append(sensorNumberStringBuffer); modelDataTypeStringBuffer.append("modelDataType"); StringBuffer modelVizStringBuffer = new StringBuffer(); modelVizStringBuffer.append(sensorNumberStringBuffer); modelVizStringBuffer.append("modelViz"); // serialNumber, its data type, and visibility (with s# prefix) StringBuffer serialNumberStringBuffer = new StringBuffer(); serialNumberStringBuffer.append(sensorNumberStringBuffer); serialNumberStringBuffer.append("serialNumber"); StringBuffer serialNumberDataTypeStringBuffer = new StringBuffer(); serialNumberDataTypeStringBuffer.append(sensorNumberStringBuffer); serialNumberDataTypeStringBuffer.append("serialNumberDataType"); StringBuffer serialNumberVizStringBuffer = new StringBuffer(); serialNumberVizStringBuffer.append(sensorNumberStringBuffer); serialNumberVizStringBuffer.append("serialNumberViz"); // sensorType, its data type, and visibility (with s# prefix) StringBuffer sensorTypeStringBuffer = new StringBuffer(); sensorTypeStringBuffer.append(sensorNumberStringBuffer); sensorTypeStringBuffer.append("sensorType"); StringBuffer sensorTypeDataTypeStringBuffer = new StringBuffer(); sensorTypeDataTypeStringBuffer.append(sensorNumberStringBuffer); sensorTypeDataTypeStringBuffer.append("sensorTypeDataType"); StringBuffer sensorTypeVizStringBuffer = new StringBuffer(); sensorTypeVizStringBuffer.append(sensorNumberStringBuffer); sensorTypeVizStringBuffer.append("sensorTypeViz"); // put all the field:datatype keyvalues for this sensor in the keyvalues map // and visibilities in the visibility map // make, data type, and visibility keyvalues.put(makeStringBuffer.toString(), values[0].split(":")[0]); keyvalues.put(makeDataTypeStringBuffer.toString(), values[0].split(":")[1]); visibility.put(makeVizStringBuffer.toString(), values[0].split(":")[2]); // model, data type, and visibility keyvalues.put(modelStringBuffer.toString(), values[1].split(":")[0]); keyvalues.put(modelDataTypeStringBuffer.toString(), values[1].split(":")[1]); visibility.put(modelVizStringBuffer.toString(), values[1].split(":")[2]); // serialNumber, data type, and visibility keyvalues.put(serialNumberStringBuffer.toString(), values[2].split(":")[0]); keyvalues.put(serialNumberDataTypeStringBuffer.toString(), values[2].split(":")[1]); visibility.put(serialNumberVizStringBuffer.toString(), values[2].split(":")[2]); // sensorType, data type, and visibility keyvalues.put(sensorTypeStringBuffer.toString(), values[3].split(":")[0]); keyvalues.put(sensorTypeDataTypeStringBuffer.toString(), values[3].split(":")[1]); visibility.put(sensorTypeVizStringBuffer.toString(), values[3].split(":")[2]); // add in default visibility visibility.put("_default", "a"); } return keyvalues; } public void setSourceProperties(Properties properties) { this.sourceProperties = properties; } }
Right now I just hardcoded the default visibility to "a", but will change that later to also be pulled from a properties file.
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erj2code over 10 yearsTom, thank you for the information. I added in the code you suggested, but when I run the program I only see the keyvalues in the JSON. For some reason I don't see the nested visibility fields. I'll attach my SensorGenerator.java class, perhaps I'm missing something :-)
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tom over 10 yearshere it is as a JUnit test. This test works for me. What version Jackson are you using? gist.github.com/TomDemeranville/7009250
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erj2code over 10 yearsI'm using camel-jackson 2.12.1. I have the following dependency in my pom.xml: <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-jackson</artifactId> <version>${camel}</version> </dependency> where I define ${camel} above as 2.12.1
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erj2code over 10 yearsI just noticed that I'm using different libraries that you are for JsonAnyGetter and JsonProperty. You are using: import com.fasterxml.jackson.annotation.JsonAnyGetter; import com.fasterxml.jackson.annotation.JsonProperty; and I'm using import org.codehaus.jackson.annotate.JsonAnyGetter; import org.codehaus.jackson.annotate.JsonProperty; Did you specify the com.fasterxml library in your pom.xml?
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tom over 10 yearsYou are using an old version. The new version uses the fasterxml namespace. I'm using Jackson 2.2.3 I think. You may have both versions on your classpath.
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erj2code over 10 yearsAre you specifying that newer version in your pom.xml or your applicationContext.xml? I looked in both and I don't seem to specify a version for the Jackson library. I guess that's why its using an older version.
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erj2code over 10 yearsHere's all I've currently specified in my applicationContext.xml for marshalling to JSON: <!-- Add Jackson library to render Java Map into JSON --> <camel:dataFormats> <camel:json id="jack" library="Jackson"/> </camel:dataFormats>
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erj2code over 10 yearsCan you post your pom.xml and Camel applicationContext.xml files with your JUnit test? I want to see if I can figure out what to add to call the newer Jackson library. Thanks.
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erj2code over 10 yearsBtw, I looked under my .classpath under my Eclipse project and found out that yes, I am specifying multiple versions of the Jackson library, i.e.: <classpathentry kind="var" path="M2_REPO/org/codehaus/jackson/jackson-asl/0.9.4/jackson-asl-0.9.4.jar"/>
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erj2code over 10 yearsAnd then further down in my .classpath I have: <classpathentry kind="lib" path="/home/accumulo/.m2/repository/org/codehaus/jackson/jackson-core-asl/1.8.8/jackson-core-asl-1.8.8.jar"> with a bunch of attributes set
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tom over 10 yearsMine is imported as a dependency of restlet 2.2-M3.
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tom over 10 yearsI'm also using <dependency> <groupId>com.fasterxml.jackson.dataformat</groupId> <artifactId>jackson-dataformat-csv</artifactId> <version>2.2.3</version> </dependency> which seems to be importing it as well. Part of my jackson is 2.1, other parts 2.2.3. Doh.
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erj2code over 10 yearsI couldn't seem to get maven to pull down the fasterxml.jackson.library, so I downloaded the jackson-annotations-2.2.3.jar and added it to my classpath. It now points my SensorGenerator class to the same library as yours, but I still don't get the nested visibility
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erj2code over 10 yearsThanks for the info. I discovered some Jackson library conflicts in my pom.xml that I'm cleaning up.