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Database Database Type for a Specific Java Class

Background

Map the column data type to the corresponding Java class.

Problem

The request returns meta information from the database:

SELECT
  rb.object_schema,
  rb.object_name,
  rb.column_name
FROM
  dictionary.resource_bundle rb

For example, this query returns (self-referential):

dictionary, resource_bundle, column_name

Where "dictionary" is the schema name, "resource_bundle" is object_name, and "column_name" is column_name.

It would be great to do something like:

SELECT
  rb.object_schema,
  rb.object_name,
  rb.column_name,
  rb.column_type
FROM
  dictionary.resource_bundle rb

And return this request:

dictionary, resource_bundle, column_name, varchar

Then use JDBC to find out what is varchar displayed before java.lang.String.

Questions

  • In PostgreSQL, how do you determine which type is used to store data, given the name of the schema, the name of the object (guaranteed to be a table or view), and the name of the column?
  • ( JDBC), ?

!

+3
2

, getMetaData, , getMetaData . :

  • java.sql.Types.
  • .

Java

:

  public String getJavaType( String schema, String object, String column )
    throws Exception {
    String fullName = schema + '.' + object + '.' + column;
    DatabaseMetaData metaData = getConnection().getMetaData();
    ResultSet columnMeta = metaData.getColumns( null, schema, object, column );
    String javaType = null;

    if( columnMeta.first() ) {
      int dataType = columnMeta.getInt( "DATA_TYPE" );
      javaType = SQLTypeMap.convert( dataType );
    }
    else {
      throw new Exception( "Unknown database column " + fullName + '.' );
    }

    return javaType;
  }

. :

import java.sql.Types;

/**
 * Converts database types to Java class types.
 */
public class SQLTypeMap {
    /**
     * Translates a data type from an integer (java.sql.Types value) to a string
     * that represents the corresponding class.
     * 
     * @param type
     *            The java.sql.Types value to convert to its corresponding class.
     * @return The class that corresponds to the given java.sql.Types
     *         value, or Object.class if the type has no known mapping.
     */
    public static Class<?> toClass(int type) {
        Class<?> result = Object.class;

        switch (type) {
            case Types.CHAR:
            case Types.VARCHAR:
            case Types.LONGVARCHAR:
                result = String.class;
                break;

            case Types.NUMERIC:
            case Types.DECIMAL:
                result = java.math.BigDecimal.class;
                break;

            case Types.BIT:
                result = Boolean.class;
                break;

            case Types.TINYINT:
                result = Byte.class;
                break;

            case Types.SMALLINT:
                result = Short.class;
                break;

            case Types.INTEGER:
                result = Integer.class;
                break;

            case Types.BIGINT:
                result = Long.class;
                break;

            case Types.REAL:
            case Types.FLOAT:
                result = Float.class;
                break;

            case Types.DOUBLE:
                result = Double.class;
                break;

            case Types.BINARY:
            case Types.VARBINARY:
            case Types.LONGVARBINARY:
                result = Byte[].class;
                break;

            case Types.DATE:
                result = java.sql.Date.class;
                break;

            case Types.TIME:
                result = java.sql.Time.class;
                break;

            case Types.TIMESTAMP:
                result = java.sql.Timestamp.class;
                break;
        }

        return result;
    }
}

, .

+15

JDBC .

JDBC- getMetaData getColumns , , .

+3

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