at org.postgresql.jdbc.BatchResultHandler.handleCompletion(BatchResultHandler.java:186)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:585)
at org.postgresql.jdbc.PgStatement.internalExecuteBatch(PgStatement.java:896)
at org.postgresql.jdbc.PgStatement.executeBatch(PgStatement.java:919)
at org.postgresql.jdbc.PgPreparedStatement.executeBatch(PgPreparedStatement.java:1685)
at Simple.main(Test.java:32)
Caused by: org.postgresql.util.PSQLException: ERROR: ON CONFLICT DO UPDATE command cannot affect row a second time
Hint: Ensure that no rows proposed for insertion within the same command have duplicate constrained values.
at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2713)
at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:2401)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:574)

package

// begin file: simple.java
import java.sql.*;
import java.util.Properties;
//
class Simple
{
public static void main(String[] args) throws SQLException {
String url = "jdbc:postgresql://localhost:5432/test?ApplicationName=test_app";
Properties properties = new Properties();
properties.setProperty("user", "db_admin");
properties.setProperty("password", "test");


 
{{    properties.setProperty("reWriteBatchedInserts", "true");
    //
    try
    \{
        Connection connection = DriverManager.getConnection(url, properties);
        // -- the property reWriteBatchedInserts is set to true
        Statement statement = connection.createStatement();
        statement.execute("create table if not exists test(id int primary key, f1 text)");
        statement.execute("truncate table test");
        PreparedStatement prepared_statement = connection.prepareStatement(
                "insert into test (id, f1) values (?, ?) ON CONFLICT (id) DO UPDATE SET f1=EXCLUDED.f1");
        prepared_statement.setInt(1, 1);
        prepared_statement.setString(2, "A");
        prepared_statement.addBatch();
        prepared_statement.setInt(1, 1);
        prepared_statement.setString(2, "B");
        prepared_statement.addBatch();
        int[] records_affected = prepared_statement.executeBatch();
        prepared_statement.close();
        statement.close();
        // --
        connection.close();
    }
    catch (SQLException e)
    \{

        throw  e;
    }