Connecting to a Database

After a database is connected, it can be used to run SQL statements to operate data.

Function Prototype

JDBC provides three database connection methods.

DriverManager.getConnection(String url)
DriverManager.getConnection(String url, Properties info)
DriverManager.getConnection(String url, String user, String password)

Parameters

**Table 1** Database connection parameters
Parameter	Description
url	gsjdbc4.jar database connection descriptor. The format is as follows: jdbc:postgresql: (The default database name is the same as the username.) jdbc:postgresql:database jdbc:postgresql://host/database (If the port number is not specified, the default port number is used.) jdbc:postgresql://host:port/database jdbc:postgresql://host:port/database?param1=value1&param2=value2 jdbc:postgresql://host1:port1,host2:port2/database?param1=value1&param2=value2 NOTE: If gsjdbc200.jar is used, replace jdbc:postgresql with jdbc:gaussdb. database indicates the name of the database to connect. host indicates the name or IP address of the database server. For security purposes, the database CN forbids access from other nodes in the cluster without authentication. To access the CN from inside the cluster, deploy the JDBC program on the host where the CN is located and set host to 127.0.0.1. Otherwise, the error message "FATAL: Forbid remote connection with trust method!" may be displayed. It is recommended that the service system be deployed outside the cluster. Otherwise, the database performance may be affected. By default, the local host is used to connect to the server. port indicates the port number of the database server. By default, the database on port 5431 of the local host is connected. param indicates a database connection attribute. The parameter can be configured in the URL. The URL starts with a question mark (?), uses an equal sign (=) to assign a value to the parameter, and uses an ampersand (&) to separate parameters. You can also use the attributes of the info object for configuration. For details, see Examples. value indicates the database connection attribute values.
info	Database connection attributes (all attributes are case sensitive). Common attributes are described as follows: PGDBNAME: string type. It specifies the database name. You do not need to set this parameter in the URL because the database name is automatically parsed from the URL. PGHOST: string type. This parameter specifies the host IP address. Use colons (:) to separate IP addresses and port numbers, and use commas (,) to separate multiple CNs. (This parameter does not need to be set in the URL. The system automatically parses the URL to obtain its value.) For details, see Examples. PGPORT: integer type. It specifies the host port number. Use colons (:) to separate IP addresses and port numbers, and use commas (,) to separate multiple CNs. (This parameter does not need to be set in the URL. The system automatically parses the URL to obtain its value.) For details, see Examples. user: string type. It specifies the database user who creates the connection. password: string type. It specifies the password of the database user. enable_ce: string type. enable_ce=1 indicates that JDBC supports the basic capability of encrypted equality query. refreshClientEncryption: string type. If refreshClientEncryption is set to 1 (default value), the encrypted database supports cache update on the client. loggerLevel: string type. The following log levels are supported: OFF, INFO, DEBUG, and TRACE. OFF indicates that the log function is disabled. The log details vary depending on the log level (INFO, DEBUG, and TRACE). The default value is null, indicating that the function is disabled. loggerFile: string type. It specifies the log output path (directory and file name). If only the file name is specified and the directory is not specified, logs are generated in the client running program directory. If no path is configured or the configured path does not exist, logs are output through flows by default. This parameter has been discarded and does not take effect. To use this parameter, you can configure it in the java.util.logging attribute file or system attributes. logger: string type. It indicates the log output framework used by the JDBC driver. The JDBC driver supports the log output framework used for interconnecting with user applications. Currently, only the third-party Slf4j-API-based log framework is supported. For details, see 6.2.9 Log Management. If this parameter is not set or is set to JDK LOGGER, JDK LOGGER is used. Otherwise, the slf4j-API-based third-party log framework must be used. allowEncodingChanges: Boolean type. If this parameter is set to true, the character set type can be changed. This parameter is used together with characterEncoding=CHARSET to set the character set. The two parameters are separated by ampersands (&). The value of characterEncoding can be UTF8, GBK, LATIN1, or GB18030. The default value is false. NOTE: When the database whose character set is GB18030_2022 is connected, setting characterEncoding to GB18030_2022 does not take effect and UTF8 is used by default. You need to set characterEncoding to GB18030 so that the GB18030_2022 characters on the server can be properly parsed. currentSchema: string type. You need to specify a schema in search-path. If the schema name contains special characters except letters, digits, and underscores (_), you are advised to enclose the schema name in quotation marks. Note that the schema name is case sensitive after quotation marks are added. If multiple schemas need to be configured, separate them with commas (,). Schemas containing special characters also need to be enclosed in quotation marks. Example: currentSchema=schema_a,"schema-b","schema/c". loadBalanceHosts: Boolean type. In the default mode (disabled), multiple hosts specified in the URL are connected in sequence. If load balancing is enabled, the shuffle algorithm is used to randomly select a host from the candidate hosts to establish a connection. autoBalance: string type. If this parameter is set to true, balance, or roundrobin, the JDBC load balancing function is enabled to balance multiple connections of an application to each CN available in the database cluster. Example: jdbc:postgresql://host1:port1,host2:port2/database?autoBalance=true. JDBC periodically obtains the list of available CNs in the entire cluster, for example, the obtained list is host1:port1,host2:port2,host3:port3,host4:port4. The refreshCNIpListTime parameter specifies the interval for obtaining the list, and the default value is 10s. Hosts obtained from the CN list are data IP addresses. When autoBalance is enabled on host1 and host2, HA is implemented only for the first connection. The driver will select available CNs from host1, host2, host3, and host4 in sequence to update the available CN list and new connections will be established on host1, host2, host3, and host4 using the RoundRobin algorithm. priorityn indicates that the JDBC-based load balancing function is enabled. Multiple connections of an application are balanced to the first n available CNs configured in the URL. When the first n CNs are unavailable, connections are randomly allocated to other available CNs in the database cluster. n is a number not less than 0 and less than the number of CNs configured in the URL. Example: jdbc:postgresql://host1:port1,host2:port2,host3:port3,host4:port4/database?autoBalance=priority2. JDBC periodically obtains the list of available CNs in the entire cluster (defined by refreshCNIpListTime). For example, the obtained list is host1:port1,host2:port2,host3:port3,host4:port4,host5:port5,host6:port6, where host1 and host2 are in AZ1, and host3 and host4 are in AZ2. The driver preferentially selects host1 and host2 for load balancing. If both host1 and host2 are unavailable, the driver randomly selects a CN from host3, host4, host5, and host6 for connection. If this parameter is set to shuffle, JDBC random load balancing is enabled to randomly and evenly distribute multiple connections of the application to available CNs in the database cluster. Example: jdbc:postgresql://host1:port1,host2:port2,host3:port3/database?autoBalance=shuffle. JDBC periodically obtains the list of available CNs in the entire cluster. For example, the obtained list is host1:port1,host2:port2,host3:port3,host4:port4. The refreshCNIpListTime parameter specifies the interval for obtaining the list, and the default value is 10s. For the first connection, host1:port1,host2:port2,host3:port3 is used for HA. For subsequent connections, the shuffle algorithm is used to randomly select a CN from the refreshed CN list. If this parameter is set to specified, the JDBC load balancing function is enabled and connections are established only on nodes specified in the user URL. Example: jdbc:postgresql://host1:port1,host2:port2,host3:port3,host4:port4/database?autoBalance=specified&priorityServers=2. JDBC identifies host1 and host2 as the connection nodes in the primary cluster, and host3 and host4 as the connection nodes in the standby cluster. First, connections are evenly established on host1 and host2. If all nodes are faulty, connections are not established on the remaining nodes in the cluster. After the standby node becomes the primary node, connections are evenly established on host3 and host4. If all nodes are faulty, connections are not established on the remaining nodes in the cluster. If this parameter is set to false, the JDBC load balancing and priority-based load balancing functions are disabled. The default value is false. CAUTION: Load balancing is based on the connection level rather than the transaction level. If the connection is persistent and the load on the connection is unbalanced, the load on the CN may be unbalanced. Load balancing can be used only in distributed scenarios and cannot be used in centralized scenarios. When load balancing is enabled, the floating IP address or data IP address can be configured in the URL. If the floating IP address is configured, the system obtains the corresponding data IP address based on the floating IP address and performs load balancing based on the obtained data IP address. Therefore, when configuring the floating IP address or data IP address in the URL, ensure that the network connection of the data IP address is normal. Otherwise, the load balancing function is abnormal. refreshCNIpListTime: integer type. This parameter specifies the interval at which JDBC periodically checks the status of CNs in the database cluster and obtains the IP address list of available CNs. The default value is 10 seconds. hostRecheckSeconds: integer type. After JDBC attempts to connect to a host, the host status is saved: connection success or connection failure. This status is trusted within the duration specified by hostRecheckSeconds. After the duration expires, the status becomes invalid. The default value is 10 seconds. ssl: Boolean type. It specifies a connection in SSL mode. When ssl is set to true, the NonValidatingFactory channel and certificate mode are supported. 1. For the NonValidatingFactory channel, configure the username and password and set SSL to true. 2. In certification mode, configure the client certificate, key, and root certificate, and set SSL to true. sslmode: string type. It specifies the SSL authentication mode. The value can be disable, allow, prefer, require, verify-ca, or verify-full. disable: SSL connection is disabled. allow: If the database server requires SSL connection, SSL connection can be enabled. However, authenticity of the database server will not be verified. prefer: If the database supports SSL connection, SSL connection is preferred. However, authenticity of the database server will not be verified. require: The system only attempts to set up an SSL connection. It neither checks whether the server certificate is issued by a trusted CA, nor checks whether the host name of the server is the same as that in the certificate. verify-ca: attempts to set up an SSL connection and checks whether the server certificate is issued by a trusted CA. verify-full: The system attempts to set up an SSL connection, checks whether the server certificate is issued by a trusted CA, and checks whether the host name of the server is the same as that in the certificate. sslcert: string type. It specifies the complete path of the certificate file. The type of the client and server certificates is End Entity. sslkey: string type. It specifies the complete path of the key file. You need to convert the client certificate to the DER format. For details, see Connecting to a Database (Using SSL). sslrootcert: string type. It specifies the name of the SSL root certificate. The root certificate type is CA. sslpassword: string type. It is provided for ConsoleCallbackHandler. sslpasswordcallback: string type. It specifies the class name of the SSL password provider. The default value is org.postgresql.ssl.jdbc4.LibPQFactory.ConsoleCallbackHandler. sslfactory: string type. It specifies the class name used by SSLSocketFactory to establish an SSL connection. sslprivatekeyfactory: string type. This parameter specifies the fully qualified name of the implementation class of the org.postgresql.ssl.PrivateKeyFactory API that implements the private key decryption method. If this parameter is not specified, try the default JDK private key decryption algorithm. If the decryption fails, use org.postgresql.ssl.BouncyCastlePrivateKeyFactory. You need to provide the bcpkix-jdk15on.jar package. The recommended version is 1.65 or later. sslfactoryarg: string type. The value is an optional parameter of the constructor function of the sslfactory class. (This parameter is not recommended.) sslhostnameverifier: string type. It specifies the class name of the host name verifier. The API must implement javax.net.ssl.HostnameVerifier. The default value is org.postgresql.ssl.PGjdbcHostnameVerifier. loginTimeout: integer type. It specifies the waiting time for establishing the database connection, in seconds. When multiple IP addresses are configured in the URL, if the time for obtaining the connection exceeds this value, the connection fails and the subsequent IP addresses are not tried. The default value is 0 (disabled). connectTimeout: integer type. It specifies the timeout interval for connecting to a server. If the time taken to connect to a server exceeds the value specified, the connection is interrupted. The unit of the timeout interval is second. The value 0 indicates that the timeout mechanism does not take effect. When multiple IP addresses are configured in the URL, this parameter indicates the timeout interval for connecting to a single IP address. The default value is 0. socketTimeout: integer type. It specifies the timeout interval for a socket read operation. If the time taken to read data from a server exceeds the value specified, the connection is closed. The unit of the timeout interval is second. The default value 0 indicates that the timeout mechanism does not take effect. socketTimeoutInConnecting: integer type. It specifies the timeout interval for a socket read operation during the connection establishment. If the time taken to read data from the server exceeds this value, it searches for the next node for connection. The unit of the timeout interval is second. The default value is 5s. statementTimeout: integer type. It specifies the timeout interval for executing a statement in a connection. If the execution time of a statement exceeds this value, the statement execution is canceled. The unit of the timeout interval is millisecond. The default value 0 indicates that the timeout mechanism does not take effect. driverInfoMode: string type. This parameter controls the output mode of the driver description information. The value can be postgresql or gaussdb. The default value is postgresql, indicating that the driver description related to PostgreSQL is displayed. If this parameter is set to gaussdb, the driver description related to GaussDB is displayed. cancelSignalTimeout: integer type. Cancel messages may cause a block. It controls connectTimeout and socketTimeout in a cancel command. The unit of the timeout interval is second. The default value is 10 seconds. tcpKeepAlive: Boolean type. It is used to enable or disable TCP keepalive detection. The default value is false. logUnclosedConnections: Boolean type. The client may leak a connection object because it does not call the connection object's close() method. These objects will be collected as garbage and finalized using the finalize() method. If the caller ignores this operation, this method closes the connection. The default value is false. assumeMinServerVersion (discarded): string type. This parameter indicates the version of the server to connect. ApplicationName: string type. This parameter specifies the name of the application that is being connected. You can query the pgxc_stat_activity table on the CN to view information about the client that is being connected. The name is displayed in the application_name column. The default value is PostgreSQL JDBC Driver. connectionExtraInfo: Boolean type. This parameter specifies whether the driver reports the driver deployment path and process owner to the database. The value can be true or false. The default value is false. If connectionExtraInfo is set to true, the JDBC driver reports the driver deployment path, process owner, and URL connection configuration information to the database and displays the information in the connection_info parameter. In this case, you can query the information from PG_STAT_ACTIVITY or PGXC_STAT_ACTIVITY. autosave: string type. The value can be always, never, or conservative. It specifies the action that the driver should perform upon a query failure. If autosave is set to always, the JDBC driver sets a savepoint before each query and rolls back to the savepoint if the query fails. If autosave is set to never, there is no savepoint. If autosave is set to conservative, a savepoint is set for each query. However, the system rolls back and retries only when there is an invalid statement. The default value is never. protocolVersion: integer type. It specifies the connection protocol version. Only versions 1 and 3 are supported. If it is set to 1, only the V1 server is connected. If it is set to 3, MD5 encryption is used. You must need to set the GUC parameter password_encryption_type to 1 to change the database encryption mode. After the cluster is restarted, create a user who uses MD5 encryption to encrypt passwords. In addition, modify the pg_hba.conf file to change the client connection mode to MD5. Log in as a new user. (You are advised not to set this parameter because the MD5 encryption algorithm has lower security and poses security risks.) NOTE: The MD5 encryption algorithm has lower security and poses security risks. Therefore, you are advised to use a more secure encryption algorithm. prepareThreshold: integer type. It specifies the number of times that the PreparedStatement object is executed before the prepared statement on the server is used. The default value is 5, indicating that when the same PreparedStatement object is executed for five or more times, the parse message is not sent to the server to parse the statement. Instead, the statement that has been parsed on the server is used. preparedStatementCacheQueries: integer type. This parameter specifies the maximum number of queries generated by the cache statement object of each connection. The default value is 256. If the number of queries generated by the statement object is greater than 256, the least recently used queries will be discarded from the cache. The value 0 indicates that the cache function is disabled. preparedStatementCacheSizeMiB: integer type. This parameter indicates the maximum size of queries generated by the cache statement object of each connection, in MB. The default value is 5. If the size of the cached queries exceeds 5 MB, the least recently used query cache will be discarded. The value 0 indicates that the cache function is disabled. databaseMetadataCacheFields: integer type. The default value is 65536. It specifies the maximum number of columns that can be cached in each connection. The value 0 indicates that the cache function is disabled. databaseMetadataCacheFieldsMiB: integer type. The default value is 5. This parameter indicates the maximum size of columns that can be cached in each connection, in MB. The value 0 indicates that the cache function is disabled. stringtype: string type. The options are unspecified and varchar. It specifies the type of the PreparedStatement parameter used by the setString() method. If stringtype is set to VARCHAR (default value), these parameters are sent to the server as varchar parameters. If stringtype is set to unspecified, these parameters are sent to the server as an untyped value, and the server attempts to infer their appropriate type. batchMode: string type. It specifies whether to connect the database in batch mode. The default value is on, indicating that the batch mode is enabled. If batchMode is set to on, the returned result is [count, 0, 0...0]. The first element in the array is the total number of records affected in batches. If batchMode is set to off, the returned result is [1, 1, 1..1]. Each element in the array corresponds to the number of affected records in a single modification. fetchsize: integer type. It specifies the default fetchsize for statements in the created connection. The default value is 0, indicating that all results are obtained at a time. It is equivalent to defaultRowFetchSize. reWriteBatchedInserts: Boolean type. During batch import, set this parameter to true to combine N insertion statements into one: insert into TABLE_NAME values(values1, ..., valuesN), ..., (values1, ..., valuesN). To use this parameter, set batchMode to off. The default value is false. unknownLength: integer type. The default value is Integer.MAX_VALUE. This parameter specifies the length of the unknown length type when the data of some PostgreSQL types (such as TEXT) is returned by functions such as ResultSetMetaData.getColumnDisplaySize and ResultSetMetaData.getPrecision. defaultRowFetchSize: integer type. It specifies the number of rows read by fetch in ResultSet at a time. Limiting the number of rows read each time in a database access request can avoid unnecessary memory consumption, thereby avoiding out of memory exception. The default value is 0, indicating that all rows are obtained at a time in ResultSet. This parameter cannot be set to a negative value. binaryTransfer: Boolean type. This parameter specifies whether data is sent and received in binary format. The default value is false. binaryTransferEnable: string type. It specifies types for which binary transmission is enabled. Every two types are separated by commas (,). You can select either the OID or name, for example, binaryTransferEnable=INT4_ARRAY,INT8_ARRAY. For example, if the OID name is BLOB and the OID number is 88, you can configure the OID as follows: binaryTransferEnable=BLOB or binaryTransferEnable=88 binaryTransferDisEnable: string type. It specifies types for which binary transmission is disabled. Every two types are separated by commas (,). You can select either the OID or name. It overwrites the setting of binaryTransferEnable. blobMode: string type. It is used to set the data type of parameters bound to the setBinaryStream method. If the value is on, the data type is blob. If the value is off, the data type is bytea. The default value is on. You are advised to set it to on for systems migrated from Oracle or MySQL and to off for systems migrated from PostgreSQL. socketFactory: string type. It specifies the name of the class used to create a socket connection with the server. This class must implement the javax.net.SocketFactory API and define a constructor with no parameter or a single string parameter. socketFactoryArg: string type. The value is an optional parameter of the constructor function of the socketFactory class and is not recommended. receiveBufferSize: integer type. It is used to set SO_RCVBUF on the connection stream. sendBufferSize: integer type. It is used to set SO_SNDBUF on the connection stream. preferQueryMode: string type. The value can be "extended", "extendedForPrepared", "extendedCacheEverything", or "simple". This parameter specifies the query mode. The default value is extended. In simple mode, only the Q message in text mode can be sent. The parse and bind messages are not supported. In extended mode, parse, bind, and execute messages are used. In extendedForPrepared mode, only the prepared statement object uses extended query, and the statement object uses only simple query. The extendedCacheEverything mode caches the query generated by each statement object. ApplicationType: string type. The value can be "not_perfect_sharding_type" or "perfect_sharding_type". It specifies whether to enable distributed write and query. The default value is not_perfect_sharding_type. Distributed write and query are enabled if this parameter is set to not_perfect_sharding_type. If it is set to perfect_sharding_type, distributed write and query are disabled by default. Distributed write and query can be performed only when */ multinode /* is added to the SQL statement. This parameter is valid only when the database is in the GTM-free scenario. priorityServers: integer type. This value is used to specify the first n nodes configured in the URL as the primary cluster to be connected preferentially. The default value is NULL. The value is a number greater than 0 and less than the number of CNs configured in the URL. It is used in streaming DR scenarios. Example: jdbc:postgresql://host1:port1,host2:port2,host3:port3,host4:port4,/database?priorityServers=2. That is, host1 and host2 are primary cluster nodes, and host3 and host4 are DR cluster nodes. usingEip: Boolean type. This value specifies whether to use an elastic IP address for load balancing. The default value is true, indicating that an elastic IP address is used for load balancing. The value false indicates that a data IP address is used for load balancing. If usingEip is set to true or left blank, the host in the URL must use an EIP. If usingEip is set to false, the host in the URL must use a data IP address. Otherwise, the priorityn load balancing policy will become invalid. traceInterfaceClass: string type. The default value is NULL, which is used to obtain the implementation class of traceId. The value is the fully qualified name of the implementation class of the org.postgresql.log.Tracer API that implements the method for obtaining traceId. use_boolean: Boolean type. It is used to set the OID type bound to the setBoolean method in extended mode. The default value is false, indicating that the int2 type is bound. The value true indicates that the Boolean type is bound. allowReadOnly: Boolean type. This parameter specifies whether the read-only mode is allowed. The default value is true, indicating that the read-only mode is allowed. If this parameter is set to false, the read-only mode is disabled. TLSCiphersSupperted: string type. It is used to set the supported TLS encryption suite. The default value is TLS_DHE_RSA_WITH_AES_128_GCM_SHA256,TLS_DHE_RSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384. stripTrailingZeros: Boolean type. The default value is false. If the value is true, trailing 0s of the numeric type are removed. It is valid only for ResultSet.getObject(int columnIndex). enableTimeZone: Boolean type. The default value is true. This parameter specifies whether to enable the time zone setting on the server. The value true indicates that the JVM time zone is obtained to specify the database time zone. The value false indicates that the database time zone is used. enableStandbyRead: Boolean type. It specifies whether to enable the read mode of the standby node. The default value is false. The value true indicates that the read mode is enabled, and the value false indicates that the read mode is disabled. oracleCompatible: string type. The default value is false. This is used to set the ORA-compatible features of driver APIs. The options are as follows: true or on: All ORA-compatible features of drivers are enabled. false or off: All ORA-compatible features of drivers are disabled. "tag1,tag2,tag3": Some ORA-compatible features of drivers are enabled. You can configure one or more tags separated by commas (,). Each tag corresponds to an ORA-compatible feature. Currently, the following tags are supported: getProcedureColumns: The behavior of the DatabaseMetaData#getProcedureColumns API is compatible with behavior ORA. batchInsertAffectedRows: After reWriteBatchedInserts is enabled, the result returned by the Statement#executeBatch API is compatible with behavior ORA. printSqlInLog: Boolean type. It specifies whether to output SQL statements in exception information or logs. The value is true (enabled) or false (disabled). The default value is true. parseCandidatesByDomain: Boolean type. Specifies whether to obtain standby nodes based on domain names. The default value is false. The value is true (enabled) or false (disabled). After this function is enabled, you need to configure the host information in the URL in the format of domain name plus port number. The driver obtains the IP address based on the domain name, generates a standby node set, and works with the autoBalance parameter for load balancing. primaryDomains: integer type. Specifies the first n domain names configured in the URL as the primary cluster to be preferentially connected. The default value is 0 (disabled). To enable the function, the value must be greater than 0 and less than the number of domain names configured in the URL. Example: jdbc:postgresql://domain1:port1,domain2:port2,domain3:port3,domain4:port4,/database?primaryDomains=2. That is, domain1 and domain2 correspond to the primary cluster, and the IP addresses corresponding to domain1 and domain2 are preferentially connected. If a primary/standby switchover occurs, domain3 and domain4 are marked as the primary cluster, and connections are preferentially established to domain3 and domain4. priorityDomains: integer type. This parameter specifies the first n node names configured in a URL as the node names to be preferentially connected. The default value is 0. To enable the function, the value must be greater than 0 and less than the number of domain names configured in the URL. If primaryDomains is configured, the value must be less than the value of primaryDomains. Example: jdbc:postgresql://domain1:port1,domain2:port2,domain3:port3,domain4:port4,/database?primaryDomains=2&priorityDomains=1. That is, domain1 and domain2 correspond to the primary cluster but the IP address corresponding to domain1 is preferentially connected. The system attempts to connect to domain2 only when domain1 cannot be connected. If a primary/standby switchover occurs, domain3 and domain4 are marked as the primary cluster. However, the IP address corresponding to domain3 is preferentially connected. If domain3 cannot be connected, the IP address corresponding to domain4 is connected. refreshDomainResolveTime: integer type. The default value is 10, in seconds. The minimum value is 1. This parameter indicates the interval for updating the domain name resolution result and takes effect only when parseCandidatesByDomain is set to true. The domain name resolution update time involved in the URL is set to a specified value and is periodically updated in the asynchronous thread.
user	Database user.
password	Password of the database user.

After the uppercaseAttributeName parameter is enabled, if the database contains metadata with a mixture of uppercase and lowercase letters, only the metadata in lowercase letters can be queried and output in uppercase letters. Before using the metadata, ensure that the metadata is stored in lowercase letters to prevent data errors.

Examples

Example 1: Connect to a database.

    
     
       
       
         // The following uses gsjdbc4.jar as an example:
// The following code encapsulates database connection operations into an API. The database can then be connected using an authorized username and a password.
public static Connection getConnect(String username, String passwd)
    {
        // Driver class.
        String driver = "org.postgresql.Driver";
        // Database connection descriptor.
        String sourceURL = "jdbc:postgresql://$ip:$port/postgres";
        Connection conn = null;
        
        try
        {
            // Load the driver.
            Class.forName(driver);
        }
        catch( Exception e )
        {
            e.printStackTrace();
            return null;
        }
        
        try
        {
             // Create a connection.
            conn = DriverManager.getConnection(sourceURL, username, passwd);
            System.out.println("Connection succeed!");
        }
        catch(Exception e)
        {
            e.printStackTrace();
            return null;
        }
        
        return conn;
    }

        

      

    
   

Example 2: Use the Properties object as a parameter to create a connection.

    
     
       
       
         // The following code uses the Properties object as a parameter to establish a connection:
public static Connection getConnectUseProp(String username, String passwd)
    {
        // Driver class.
        String driver = "org.postgresql.Driver";
        // Database connection descriptor.
        String sourceURL = "jdbc:postgresql://$ip:$port/postgres?autoBalance=true";
        Connection conn = null;
        Properties info = new Properties();
        
        try
        {
            // Load the driver.
            Class.forName(driver);
        }
        catch( Exception e )
        {
            e.printStackTrace();
            return null;
        }
        
        try
        {
             info.setProperty("user", username);
             info.setProperty("password", passwd);
             // Create a connection.
             conn = DriverManager.getConnection(sourceURL, info);
             System.out.println("Connection succeed!");
        }
        catch(Exception e)
        {
            e.printStackTrace();
            return null;
        }
        
        return conn;
    }

        

      

    
   