如何使用 Java PreparedStatement 将 JSON 对象插入 Postgres？

Question

I'm struggling to insert a JSON object into my postgres v9.4 DB. I have defined the column called "evtjson" as type json (not jsonb ).

I am trying to use a prepared statement in Java (jdk1.8) to insert a Json object (built using JEE javax.json libraries) into the column, but I keep running into SQLException errors.

I create the JSON object using:

JsonObject mbrLogRec = Json.createObjectBuilder().build();
…
mbrLogRec = Json.createObjectBuilder()
                .add("New MbrID", newId)
                .build();

Then I pass this object as a parameter to another method to write it to the DB using a prepared statement. (along with several other fields) As:

pStmt.setObject(11, dtlRec);

Using this method, I receive the following error:

org.postgresql.util.PSQLException: No hstore extension installed. at org.postgresql.jdbc.PgPreparedStatement.setMap(PgPreparedStatement.java:553) at org.postgresql.jdbc.PgPreparedStatement.setObject(PgPreparedStatement.java:1036)

I have also tried:

pStmt.setString(11, dtlRec.toString());
pStmt.setObject(11, dtlRec.toString());

Which produce a different error:

Event JSON: {"New MbrID":29}

SQLException: ERROR: column "evtjson" is of type json but expression is of type character varying

Hint: You will need to rewrite or cast the expression.

But, at least this tells me that the DB is recognizing the column as type JSON. I did try installing the hstore extension, but it then told me that it was not an hstore object.

OracleDocs shows a number of various methods to set the parameter value in the preparedStatement, but I'd rather not try them all if someone knows the answer. ( http://docs.oracle.com/javase/8/docs/api/java/sql/PreparedStatement.html ) These also reference an additional parameter, SQLType, but I can't find any reference to these.

Should I try setAsciiStream ? CharacterStream ? CLOB?

Answer 1

This behaviour is quite annoying since JSON strings are accepted without problems when used as literal strings in SQL commands.

There is a already an issue for this in the postgres driver Github repository (even if the problem seems the be the serverside processing).

Besides using a cast (see answer of @a_horse_with_no_name) in the sql string, the issue author offers two additional solutions:

1. Use a parameter stringtype=unspecified in the JDBC connection URL/options.

This tells PostgreSQL that all text or varchar parameters are actually of unknown type, letting it infer their types more freely.

2. Wrap the parameter in a org.postgresql.util.PGobject :

 PGobject jsonObject = new PGobject();
 jsonObject.setType("json");
 jsonObject.setValue(yourJsonString);
 pstmt.setObject(11, jsonObject);

Answer 2

You can do it like this and you just need the json string:

Change the query to:

String query = "INSERT INTO table (json_field) VALUES (to_json(?::json))"

And set the parameter as a String.

pStmt.setString(1, json);

Answer 3

Passing the JSON as a String is the right approach, but as the error message tells you, you need to cast the parameter in the INSERT statement to a JSON value:

insert into the_table
   (.., evtjson, ..) 
values 
   (.., cast(? as json), ..)

Then you can use pStmt.setString(11, dtlRec.toString()) to pass the value

Answer 4

You have two options:

1. Use statement.setString(jsonStr) and then handle the conversion in the sql statement:

`

PreparedStatement statement = con.prepareStatement("insert into table 
 (jsonColumn) values (?::json)");
 statement.setString(1, jsonStr);

2. Another option is to use PGobject to create a custom value wrapper.

PGobject jsonObject = new PGobject();
 PreparedStatement statement = con.prepareStatement("insert into table 
 (jsonColumn) values (?)");
 jsonObject.setType("json");
 jsonObject.setValue(jsonStr);
 statement.setObject(1, jsonObject);

` I personally prefer the latter as the query is cleaner

Answer 5

As others have mentioned, your SQL string needs to explicitly cast the bind value to the PostgreSQL json or jsonb type:

insert into t (id, j) values (?, ?::json)

Now you can bind the string value. Alternatively, you can use a library that can do it, for example jOOQ (works out of the box) or Hibernate (using a third party UserType registration). The benefits of this is that you don't have to think about this every time you bind such a variable (or read it). A jOOQ example:

ctx.insertInto(T)
   .columns(T.ID, T.J)
   .values(1, JSON.valueOf("[1, 2, 3]"))
   .execute();

Behind the scenes, the same cast as above is always generated, whenever you work with thisJSON (or JSONB ) data type.

(Disclaimer: I work for the company behind jOOQ)

Answer 6

Most answers here defines ways of inserting into postgres json field with jdbc in a non-standard way, ie. it is db implementation specific. If you need to insert a java string into a postgres json field with pure jdbc and pure sql use:

preparedStatement.setObject(1, "{}", java.sql.Types.OTHER)

This will make the postgres jdbc driver (tested with org.postgresql:postgresql:42.2.19) convert the java string to the json type. It will also validate the string as being a valid json representation, something that various answers using implicit string casts does not do - resulting in the possibility of corrupt persisted json data.

Answer 7

PostgreSQL is excessively, annoyingly strict about data type conversions. It won't implicitly cast text even to text-like values such as xml and json.

so the original solution in this answer bypasses JSON validation by

create cast (CHARACTER VARYING as json) without function as implicit;

here CHARACTER VARYING is actually you are trying to pass to your prepared statement object.

Answer 8

if using spring boot: adding the following line to application.properties helped:

spring.datasource.hikari.data-source-properties.stringtype=unspecified

as Wero wrote:

This tells PostgreSQL that all text or varchar parameters are actually of unknown type

Answer 9

Instead of passing json object pass its string value and cast it to json in the query. Example:

JSONObject someJsonObject=..........

String yourJsonString = someJsonObject.toString();

String query = "INSERT INTO table (json_field) VALUES (to_json(yourJsonString::json))";

this worked for me.