The HyperSQL hsql: and hsqls: protocol network database server.

A Server object acts as a network database server and is one way of using the client-server mode of HSQLDB Database Engine. Instances of this class handle native HSQL protocol connections exclusively, allowing database queries to be performed efficiently across the network. Server's direct descendant, WebServer, handles HTTP protocol connections exclusively, allowing HSQL protocol to be tunnelled over HTTP to avoid sandbox and firewall issues, albeit less efficiently.

There are a number of ways to configure and start a Server instance.

When started from the command line or programatically via the main(String[]) method, configuration occurs in three phases, with later phases overriding properties set by previous phases:

1. Upon construction, a Server object is assigned a set of default properties.
2. If it exists, properties are loaded from a file named 'server.properties' in the present working directory.
3. The command line arguments (alternatively, the String[] passed to main()) are parsed and used to further configure the Server's properties.

From the command line, the options are as follows:

+-----------------+-------------+----------+------------------------------+
|    OPTION       |    TYPE     | DEFAULT  |         DESCRIPTION          |
+-----------------+-------------+----------+------------------------------|
| --help          |             |          | prints this message          |
| --address       | name|number | any      | server inet address          |
| --port          | number      | 9001/544 | port at which server listens |
| --database.i    | [type]spec  | 0=test   | path of database i           |
| --dbname.i      | alias       |          | url alias for database i     |
| --silent        | true|false  | true     | false => display all queries |
| --trace         | true|false  | false    | display JDBC trace messages  |
| --tls           | true|false  | false    | TLS/SSL (secure) sockets     |
| --no_system_exit| true|false  | false    | do not issue System.exit()   |
| --remote_open   | true|false  | false    | can open databases remotely  |
| --props         | filepath    |          | file path of properties file |
+-----------------+-------------+----------+------------------------------+

The database.i and dbname.i options need further explanation:

• Multiple databases can be served by each instance of the Server. The value of i is currently limited to the range 0..9, allowing up to 10 different databases. Any number is this range can be used.
• The value assigned to database.i is interpreted using the format '[type]spec', where the optional type component is one of 'file:', 'res:' or 'mem:' and the spec component is interpreted in the context of the type component.

  If omitted, the type component is taken to be 'file:'.

  A full description of how '[type]spec' values are interpreted appears in the overview for JDBCConnection.

• The value assigned to dbname.i is taken to be the key used to look up the desired database instance and thus corresponds to the <alias> component of the HSQLDB HSQL protocol database connection url: 'jdbc:hsqldb:hsql[s]://host[port][/<alias>]'.
• The value of database.0 is special. If dbname.0 is not specified, then this defaults to an empty string and a connection is made to database.0 path when the <alias> component of an HSQLDB HSQL protocol database connection url is omitted. If a database key/value pair is found in the properties when the main method is called, this pair is supersedes the database.0 setting

  This behaviour allows the previous database connection url format to work with essentially unchanged semantics.

• When the remote_open property is true, a connection attempt to an unopened database results in the database being opened. The URL for connection should include the property filepath to specify the path. 'jdbc:hsqldb:hsql[s]://host[port]/<alias>;filepath=hsqldb:file:<database path>'. the given alias and filepath value will be associated together. The database user and password to start this connection must be valid. If this form of connection is used again, after the database has been opened, the filepath property is ignored.
• Once an alias such as "mydb" has been associated with a path, it cannot be reassigned to a different path.
• If a database is closed with the SHUTDOWN command, its alias is removed. It is then possible to connect to this database again with a different (or the same) alias.
• If the same database is connected to via two different aliases, and then one of the is closed with the SHUTDOWN command, the other is also closed.

From the 'server.properties' file, options can be set similarly, using a slightly different format.

Here is an example 'server.properties' file:

server.port=9001
server.database.0=test
server.dbname.0=...
...
server.database.n=...
server.dbname.n=...
server.silent=true

Starting with 1.7.2, Server has been refactored to become a simple JavaBean with non-blocking start() and stop() service methods. It is possible to configure a Server instance through the JavaBean API as well, but this part of the public interface is still under review and will not be finalized or documented fully until the final 1.7.2 release.

Note:

The 'no_system_exit' property is of particular interest.

If a Server instance is to run embedded in, say, an application server, such as when the JDBCDataSource or HsqlServerFactory classes are used, it is typically necessary to avoid calling System.exit() when the Server instance shuts down.

By default, 'no_system_exit' is set:

1. true when a Server is started directly from the start() method.
2. false when a Server is started from the main(String[]) method.

These values are natural to their context because the first case allows the JVM to exit by default on Server shutdown when a Server instance is started from a command line environment, whereas the second case prevents a typically unwanted JVM exit on Server shutdown when a Server instance is started as part of a larger framework.