Generic Enum converter for iBatis

My goal was to create a simple, extensible Enum converter that would work with

iBatis. This seems like a trivial problem, but took me a while to find a proper solution. There were some additional preconditions:
* all given Enums are jaxb generated objects – but any standard Java Enum should work
* conversion was 1-to-1, no special conditions and processing The example Enum for this problem looks like this one (copy&paste from jaxb generated source):

@XmlType(name ="ServiceType") 
@XmlEnum
public enum ServiceType {

    @XmlEnumValue("stationary")
    STATIONARY("stationary"),
    @XmlEnumValue("mobile")
    MOBILE("mobile");
    private final String value;

    ServiceType(String v) {
        value = v;
    }

    public String value() {
        return value;
    }

    public static ServiceType fromValue(String v) {
        for (ServiceType c: ServiceType.values()) {
            if (c.value.equals(v)) {
                return c;
            }
        }
        throw new IllegalArgumentException(v);
    }

}

“No big deal”, you say. I beg to differ. What I wanted to achieve was a simple construction which would look like this when used for another Enum (CommonEnumTypeHandler is the name of my generic converter):

public class ServiceTypeHandler extends CommonEnumTypeHandler { }

Unfortunately due to the fact, that Java does not have reified generics, which is described in

multiple places, I had to stick with passing through a Class type of my enum. So it looks like this:

public class ServiceTypeHandler extends CommonEnumTypeHandler {

    public ServiceTypeHandler() {
        super(ServiceType.class);
    }
}

My final class has to look like this one below:

import java.sql.SQLException;

import com.ibatis.sqlmap.client.extensions.ParameterSetter;
import com.ibatis.sqlmap.client.extensions.ResultGetter;
import com.ibatis.sqlmap.client.extensions.TypeHandlerCallback;

public abstract class CommonEnumTypeHandler implements TypeHandlerCallback {

    Class enumClass;

    public CommonEnumTypeHandler(Class clazz) {
        this.enumClass = clazz;
    }

    public void setParameter(ParameterSetter ps, Object o) throws SQLException {
        if (o.getClass().isAssignableFrom(enumClass)) {
            ps.setString(((T) o).name().toUpperCase());
        } else
            throw new SQLException("Excpected " + enumClass + " object than: " + o);
    }

    public Object getResult(ResultGetter rs) throws SQLException {
        Object o = valueOf(rs.getString());
        if (o == null)
            throw new SQLException("Unknown parameter type: " + rs.getString());
        return o;
    }

    public Object valueOf(String s) {
        return Enum.valueOf(enumClass, s.toUpperCase());
    }
}

 

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Need to make a quick json fixes – JSONPath for rescue

From time to time I have a need to do some fixes in my json data. In a world of flat files I do this with grep/sed/awk tool chain. How to handle it for JSON? Searching for a solution I came across the JSONPath. It quite mature tool (from 2007) but I haven't hear about it so I decided to share my experience with others.

First of all you can try it without pain online: http://jsonpath.curiousconcept.com/. Full syntax is described at http://goessner.net/articles/JsonPath/



But also you can download python binding and run it from command line:
$ sudo apt-get install python-jsonpath-rw
$ sudo apt-get install python-setuptools
$ sudo easy_install -U jsonpath

After that you can use inside python or with simple cli wrapper:
#!/usr/bin/python
import sys, json, jsonpath

path = sys.argv[
1]

result = jsonpath.jsonpath(json.load(sys.stdin), path)
print json.dumps(result, indent=2)

… you can use it in your shell e.g. for json:
{
"store": {
"book": [
{
"category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
},
{
"category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
},
{
"category": "fiction",
"author": "Herman Melville",
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"price": 8.99
},
{
"category": "fiction",
"author": "J. R. R. Tolkien",
"title": "The Lord of the Rings",
"isbn": "0-395-19395-8",
"price": 22.99
}
],
"bicycle": {
"color": "red",
"price": 19.95
}
}
}

You can print only book nodes with price lower than 10 by:
$ jsonpath '$..book[?(@.price 

Result:
[
{
"category": "reference",
"price": 8.95,
"title": "Sayings of the Century",
"author": "Nigel Rees"
},
{
"category": "fiction",
"price": 8.99,
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"author": "Herman Melville"
}
]

Have a nice JSON hacking!From time to time I have a need to do some fixes in my json data. In a world of flat files I do this with grep/sed/awk tool chain. How to handle it for JSON? Searching for a solution I came across the JSONPath. It quite mature tool (from 2007) but I haven't hear about it so I decided to share my experience with others.