Class MetadataWriter

All Implemented Interfaces:

public class MetadataWriter extends MetadataSource
A connection to a metadata database with write capabilities. The database must have a schema of the given name, which can be initially empty. Tables and columns are created as needed when the add(Object) method is invoked.

No more than one instance of Metadata­Writer should be used for the same database. However multiple instances of Metadata­Source can be used concurrently with a single Metadata­Writer instance on the same database.


The constructor expects three Java arguments (the metadata standard, the data source and the database schema) completed by an arbitrary amount of optional arguments given as a map of properties. The following keys are recognized by Metadata­Source and all other entries are ignored:
Optional properties at construction time
Key Value type Description
"catalog" String The database catalog where the metadata schema is stored.
"classloader" ClassLoader The class loader to use for creating Proxy instances.
"maxStatements" Integer Maximal number of Prepared­Statements that can be kept simultaneously open.
"maximumIdentifierLength" Integer The maximal number of characters allowed for primary keys. This is the value given to the VARCHAR type when creating new "ID" columns.
"maximumValueLength" Integer Maximal number of characters allowed in text columns. This is the parameter given to the VARCHAR type when creating new columns. Attempts to insert a text longer than this limit will typically throws a SQLException, but the exact behavior is database-dependent.
"columnCreationPolicy" ValueExistencePolicy Whether columns should be created only for non-empty attributes (NON_EMPTY, the default) or for all attributes (ALL)

Defined in the sis-metadata module

  • Constructor Details

    • MetadataWriter

      public MetadataWriter(MetadataStandard standard, DataSource dataSource, String schema, Map<String,?> properties)
      Creates a new metadata writer.
      standard - the metadata standard to implement.
      data­Source - the source for getting a connection to the database.
      schema - the database schema were metadata tables are stored, or null if none.
      properties - additional options, or null if none. See class javadoc for a description.
  • Method Details

    • add

      public String add(Object metadata) throws MetadataStoreException
      Adds the given metadata object to the database, if it does not already exists. If the database already contains a metadata equals to the given one, then the database is left unchanged and the identifier of the existing metadata is returned.
      metadata - the metadata object to add.
      the identifier (primary key) of the metadata just added, or the identifier of the existing metadata is one exists.
      Metadata­Store­Exception - if the metadata object does not implement a metadata interface of the expected package, if an exception occurred while reading or writing the database. In such case, the database content is left unchanged (i.e. this method is a all or nothing operation).
    • suggestIdentifier

      protected String suggestIdentifier(Object metadata, Map<String,Object> asValueMap) throws SQLException
      Suggests an identifier (primary key) to be used for the given metadata. This method is invoked automatically when a new metadata is about to be inserted in the database. The default implementation uses heuristic rules for a few "well known" metadata like Identifier and Citation. Subclasses can override this method for implementing their own heuristic.

      This method does not need to care about key collision. The caller will adds some suffix if this is necessary for differentiating otherwise identical identifiers.

      metadata - the metadata instance for which to suggests an identifier.
      as­Value­Map - a view of all metadata properties as a map. Keys are UML identifiers.
      the proposed identifier, or null if this method does not have any suggestion.
      SQLException - if an access to the database was desired but failed.