EDIT: Marcus(1st comment provider) helped me to write much cleaner and secure code. It doesn’t require CAST function and uses PGobject with jdbc’s setObject. You could download updated code from git-repo. Thanks Marcus !!
One of the clients of OmniTI requested help to provide sample application to insert JSON data into Postgres using Java JDBC driver . I’m not Java expert so it took a while for me to write a simple java code to insert data. TBH, I took help to write test application from one of our Java engineers at OmniTI. Now, test application is ready and next step is to make it work with JSON datatype ! After struggling a little to find out work around for string escaping in JAVA code, I stumbled upon data type issue! Here is the test application code to connect to my local Postgres installation and insert JSON data into sample table:
postgres=# \d sample
Table "public.sample"
Column | Type | Modifiers
--------+---------+-----------
id | integer |
data | json |
denishs-MacBook-Air-2:java denish$ java -cp $CLASSPATH PgJSONExample
-------- PostgreSQL JDBC Connection Testing ------------
PostgreSQL JDBC Driver Registered!
You made it, take control your database now!
Something exploded running the insert: ERROR: column "data" is of type json but expression is of type character varying
Hint: You will need to rewrite or cast the expression.
Position: 42
After some research , I found out that there is no standard JSON type on java side so adding support for json to postgres jdbc is not straight forward ! StackOverflow answer helped me for testing out the JSON datatype handling at psql level. As Craig mentioned in the answer that the correct way to solve this problem is to write a custom Java mapping type that uses the JDBC setObject method. This can be a tricky though. A simpler workaround is to tell PostgreSQL to cast implicitly from text to json:
postgres=# create cast (text as json) without function as implicit;
CREATE CAST
The WITHOUT FUNCTION clause is used because text and json have the same on-disk and in-memory representation, they’re basically just aliases for the same data type. AS IMPLICIT tells PostgreSQL it can convert without being explicitly told to, allowing things like this to work:
postgres=# prepare test(text) as insert into sample (data) values ($1);
PREPARE
postgres=# execute test('{}');
INSERT 0 1
postgres=# select data from sample;
data
----
{}
(1 row)
Awesome ! That worked 
Let’s try similar approach in Java application code.
denishs-MacBook-Air-2:java denish$ export CLASSPATH=/usr/share/postgresql/java/postgresql-9.2-1002.jdbc4.jar:
denishs-MacBook-Air-2:java denish$ javac -classpath $CLASSPATH PgJSONExample.java
denishs-MacBook-Air-2:java denish$ java -cp $CLASSPATH PgJSONExample
-------- PostgreSQL JDBC Connection Testing ------------
PostgreSQL JDBC Driver Registered!
You made it, take control your database now!
postgres=# select * from sample;
id | data
----+------------------------------------------------------------------------
1 | {"username":"denish","posts":10122,"emailaddress":"denish@omniti.com"}
(1 row)
Yay! It worked as well
Next in my list to figure out installing PL/Java on Mac and/or Linux !! Let me know, if you have instructions for installation and test application using PL/Java.
