The ORA-12705 error typically occurs when Oracle cannot find or access National Language Support (NLS) data files during database operations. In JDBC connections, this often manifests when:

• The Oracle client environment isn't properly configured
• NLS_LANG parameter mismatches exist between client and server
• File permissions prevent access to NLS data
• ORACLE_HOME path is incorrectly set

Before diving into solutions, verify these critical points:

// Check your current NLS settings in SQL*Plus
SELECT * FROM nls_session_parameters;
SELECT * FROM v$nls_parameters;

Compare these with your Java environment's NLS settings using:

System.getProperties().list(System.out);

Solution 1: Explicit NLS_LANG Specification

Modify your connection code to explicitly set NLS parameters:

import java.sql.*;
import java.util.Properties;

public class OracleConnect {
    public static void main(String[] args) {
        String url = "jdbc:oracle:thin:@hostname:1521:oracle";
        Properties props = new Properties();
        props.put("user", "username");
        props.put("password", "password");
        props.put("oracle.jdbc.defaultNChar", "false");
        props.put("oracle.net.ns_lang", "AMERICAN_AMERICA.AL32UTF8");
        
        try (Connection con = DriverManager.getConnection(url, props)) {
            System.out.println("Connection successful!");
        } catch (SQLException ex) {
            ex.printStackTrace();
        }
    }
}

Solution 2: Environment Variable Verification

Ensure these environment variables are properly set before Java execution:

export NLS_LANG=AMERICAN_AMERICA.AL32UTF8
export ORACLE_HOME=/path/to/oracle/client
export LD_LIBRARY_PATH=$ORACLE_HOME/lib:$LD_LIBRARY_PATH

Case: Missing NLS Data Files

If the error persists, verify NLS data file presence in:

$ORACLE_HOME/nls/data

Common required files include:

• lx00001.nlb
• lx10001.nlb
• lx20001.nlb

Case: Multiple Oracle Homes Conflict

When multiple Oracle installations exist, force the correct home:

// In Java code before connection
System.setProperty("oracle.net.tns_admin", "/correct/path/to/network/admin");
System.setProperty("oracle.home", "/correct/oracle/home");

For ojdbc6.jar or later drivers, try these connection properties:

props.put("oracle.jdbc.useNio", "false");
props.put("oracle.jdbc.convertNioHeapBuffers", "false");

For connection pools (like HikariCP), configure as follows:

HikariConfig config = new HikariConfig();
config.setJdbcUrl("jdbc:oracle:thin:@hostname:1521:oracle");
config.addDataSourceProperty("oracle.jdbc.defaultNChar", "false");
config.addDataSourceProperty("oracle.net.ns_lang", "AMERICAN_AMERICA.AL32UTF8");
// Other pool configurations...

Check database server NLS configuration:

-- As DBA
SELECT * FROM v$nls_valid_values WHERE parameter = 'LANGUAGE';
SELECT * FROM v$nls_valid_values WHERE parameter = 'TERRITORY';
SELECT * FROM v$nls_valid_values WHERE parameter = 'CHARACTERSET';

Ensure server and client NLS settings are compatible. Common recommended pairings:

Server Setting	Recommended Client Setting
AMERICAN_AMERICA.AL32UTF8	AMERICAN_AMERICA.AL32UTF8 or AMERICAN_AMERICA.UTF8
AMERICAN_AMERICA.WE8ISO8859P1	AMERICAN_AMERICA.WE8ISO8859P1

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You're working with Oracle 10gR2 on RHEL 4.0, successfully connecting via SQL*Plus and iSQL*Plus, but when your Java application tries to establish a JDBC connection, it throws:

java.sql.SQLException: ORA-00604: error occurred at recursive SQL level 1
ORA-12705: Cannot access NLS data files or invalid environment specified

The ORA-12705 error typically occurs when Oracle cannot find or properly access its National Language Support (NLS) data files. This is particularly common in Java applications because:

• The Oracle client environment isn't properly initialized in the JVM context
• NLS-related environment variables aren't properly set
• There's a mismatch between the Oracle client version and database version

Solution 1: Explicitly Set NLS Environment Variables

Before establishing the connection, set these properties in your Java code:

System.setProperty("oracle.jdbc.defaultNChar", "true");
System.setProperty("oracle.net.ns_charset", "UTF8");
System.setProperty("user.language", "en");
System.setProperty("user.region", "US");

Solution 2: Verify Oracle Client Configuration

Ensure your Oracle client installation has these critical files:

• $ORACLE_HOME/nls/data/*.nlb
• $ORACLE_HOME/nls/mesg/*.msb

If files are missing, reinstall the Oracle client or copy them from another working installation.

Solution 3: Use OCI Driver Instead of Thin Driver

Modify your connection URL:

String url = "jdbc:oracle:oci:@hostname:1521:oracle";

Note: This requires Oracle client libraries to be installed on the host.

Here's a robust connection example with error handling:

import java.sql.*;

public class OracleConnector {
    public static void main(String[] args) {
        // Set NLS environment before any Oracle calls
        System.setProperty("oracle.jdbc.defaultNChar", "true");
        
        String url = "jdbc:oracle:thin:@hostname:1521:oracle";
        String user = "username";
        String pass = "password";
        
        try {
            // Explicitly load driver (not always needed in newer JDBC)
            Class.forName("oracle.jdbc.driver.OracleDriver");
            
            // Set connection properties
            java.util.Properties props = new java.util.Properties();
            props.setProperty("user", user);
            props.setProperty("password", pass);
            props.setProperty("defaultNChar", "true");
            
            Connection conn = DriverManager.getConnection(url, props);
            
            // Verify connection
            try (Statement stmt = conn.createStatement();
                 ResultSet rs = stmt.executeQuery("SELECT * FROM v$version")) {
                while (rs.next()) {
                    System.out.println(rs.getString(1));
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

If the issue persists:

1. Check $ORACLE_HOME environment variable points to correct location
2. Verify LD_LIBRARY_PATH includes $ORACLE_HOME/lib
3. Ensure the Oracle user has read permissions on NLS files
4. Try setting NLS_LANG environment variable explicitly: export NLS_LANG=AMERICAN_AMERICA.AL32UTF8

Remember that Oracle 10gR2 is quite old, and upgrading to a supported version might resolve many compatibility issues.