Connecting to the Database

Connecting to the Database
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With JDBC, a database is represented by a URL (Uniform Resource Locator). With PostgreSQL™, this takes one of the following forms:

```
jdbc:postgresql:database
```
```
jdbc:postgresql://host/database
```
```
jdbc:postgresql://host:port/database
```

The parameters have the following meanings:

host

The host name of the server. Defaults to localhost. To specify an IPv6 address your must enclose the host parameter with square brackets, for example:

jdbc:postgresql://[::1]:5740/accounting

port

The port number the server is listening on. Defaults to the PostgreSQL™ standard port number (5432).

database

The database name.

To connect, you need to get a Connection instance from JDBC. To do this, you use the DriverManager.getConnection() method:

Connection db = DriverManager.getConnection(url, username, password);

Connection Parameters

In addition to the standard connection parameters the driver supports a number of additional properties which can be used to specify additional driver behavior specific to PostgreSQL™. These properties may be specified in either the connection URL or an additional Properties object parameter to DriverManager.getConnection. The following examples illustrate the use of both methods to establish a SSL connection.

String url = "jdbc:postgresql://localhost/test";
Properties props = new Properties();
props.setProperty("user","fred");
props.setProperty("password","secret");
props.setProperty("ssl","true");
Connection conn = DriverManager.getConnection(url, props);

String url = "jdbc:postgresql://localhost/test?user=fred&password=secret&ssl=true";
Connection conn = DriverManager.getConnection(url);

user = String

The database user on whose behalf the connection is being made.

password = String

The database user's password.

ssl

Connect using SSL. The driver must have been compiled with SSL support. This property does not need a value associated with it. The mere presence of it specifies a SSL connection. However, for compatibility with future versions, the value "true" is preferred. For more information see Chapter 4, Using SSL.

sslfactory = String

The provided value is a class name to use as the SSLSocketFactory when establishing a SSL connection. For more information see the section called “Custom SSLSocketFactory”.

sslfactoryarg = String

This value is an optional argument to the constructor of the sslfactory class provided above. For more information see the section called “Custom SSLSocketFactory”.

compatible = String

Act like an older version of the driver to retain compatibility with older applications. At the moment this controls two driver behaviors: the handling of binary data fields, and the handling of parameters set via setString()

Older versions of the driver used this property to also control the protocol used to connect to the backend. This is now controlled by the protocolVersion property.

Information on binary data handling is detailed in Chapter 7, Storing Binary Data. To force the use of Large Objects set the compatible property to 7.1.

When compatible is set to 7.4 or below, the default for the stringtype parameter is changed to unspecified.

protocolVersion = String

The driver supports both the V2 and V3 frontend/backend protocols. The V3 protocol was introduced in 7.4 and the driver will by default try to connect using the V3 protocol, if that fails it will fall back to the V2 protocol. If the protocolVersion property is specified, the driver will try only the specified protocol (which should be either "2" or "3"). Setting protocolVersion to "2" may be used to avoid the failed attempt to use the V3 protocol when connecting to a version 7.3 or earlier server, or to force the driver to use the V2 protocol despite connecting to a 7.4 or greater server.

loglevel = int

Set the amount of logging information printed to the DriverManager's current value for LogStream or LogWriter. It currently supports values of org.postgresql.Driver.DEBUG (2) and org.postgresql.Driver.INFO (1). INFO will log very little information while DEBUG will produce significant detail. This property is only really useful if you are a developer or are having problems with the driver.

charSet = String

The character set to use for data sent to the database or recieved from the database. This property is only relevent for server versions less than or equal to 7.2. The 7.3 release was the first with multibyte support compiled by default and the driver uses its character set translation facilities instead of trying to do it itself.

allowEncodingChanges = boolean

When using the V3 protocol the driver monitors changes in certain server configuration parameters that should not be touched by end users. The client_encoding setting is set by the driver and should not be altered. If the driver detects a change it will abort the connection. There is one legitimate exception to this behavior though, using the COPY command on a file residing on the server's filesystem. The only means of specifying the encoding of this file is by altering the client_encoding setting. The JDBC team considers this a failing of the COPY command and hopes to provide an alternate means of specifying the encoding in the future, but for now there is this URL parameter. Enable this only if you need to override the client encoding when doing a copy.

logUnclosedConnections = boolean

Clients may leak Connection objects by failing to call its close() method. Eventually these objects will be garbage collected and the finalize() method will be called which will close the Connection if caller has neglected to do this himself. The usage of a finalizer is just a stopgap solution. To help developers detect and correct the source of these leaks the logUnclosedConnections URL parameter has been added. It captures a stacktrace at each Connection opening and if the finalize() method is reached without having been closed the stacktrace is printed to the log.

prepareThreshold = int

Determine the number of PreparedStatement executions required before switching over to use server side prepared statements. The default is five, meaning start using server side prepared statements on the fifth execution of the same PreparedStatement object. More information on server side prepared statements is available in the section called “Server Prepared Statements”.

loginTimeout = int

Specify how long to wait for establishment of a database connection. The timeout is specified in seconds.

stringtype = String

Specify the type to use when binding PreparedStatement parameters set via setString(). If stringtype is set to varchar (the default), such parameters will be sent to the server as varchar parameters. If stringtype is set to unspecified, parameters will be sent to the server as untyped values, and the server will attempt to infer an appropriate type. This is useful if you have an existing application that uses setString() to set parameters that are actually some other type, such as integers, and you are unable to change the application to use an appropriate method such as setInt().

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