Establishing a Connection建立联系

First, you need to establish a connection with the data source you want to use.首先，需要与要使用的数据源建立连接。A data source can be a DBMS, a legacy file system, or some other source of data with a corresponding JDBC driver.数据源可以是DBMS、遗留文件系统，也可以是具有相应JDBC驱动程序的其他数据源。Typically, a JDBC application connects to a target data source using one of two classes:通常，JDBC应用程序使用以下两个类之一连接到目标数据源：

• DriverManager: This fully implemented class connects an application to a data source, which is specified by a database URL.：此完全实现的类将应用程序连接到由数据库URL指定的数据源。When this class first attempts to establish a connection, it automatically loads any JDBC 4.0 drivers found within the class path.当该类首次尝试建立连接时，它会自动加载在类路径中找到的任何JDBC 4.0驱动程序。Note that your application must manually load any JDBC drivers prior to version 4.0.请注意，应用程序必须手动加载4.0版之前的任何JDBC驱动程序。

• DataSource: This interface is preferred over DriverManager because it allows details about the underlying data source to be transparent to your application.：此接口优于DriverManager，因为它允许底层数据源的详细信息对应用程序透明。A DataSource object's properties are set so that it represents a particular data source.DataSource对象的属性被设置为表示特定的数据源。See Connecting with DataSource Objects for more information.有关详细信息，请参阅连接数据源对象。For more information about developing applications with the DataSource class, see the latest The Java EE Tutorial.有关使用DataSource类开发应用程序的更多信息，请参阅最新的Java EE教程。

Note注意: The samples in this tutorial use the DriverManager class instead of the DataSource class because it is easier to use and the samples do not require the features of the DataSource class.：本教程中的示例使用DriverManager类而不是DataSource类，因为它更易于使用，并且示例不需要DataSource类的功能。

This page covers the following topics:本页涵盖以下主题：

• Using the DriverManager Class使用DriverManager类
• Specifying Database Connection URLs指定数据库连接URL

Using the DriverManager Class使用DriverManager类

Connecting to your DBMS with the DriverManager class involves calling the method DriverManager.getConnection.使用DriverManager类连接到DBMS需要调用DriverManager.getConnection方法。The following method, JDBCTutorialUtilities.getConnection, establishes a database connection:以下方法JDBCTutorialUtilities.getConnection用于建立数据库连接：

public Connection getConnection() throws SQLException {

    Connection conn = null;
    Properties connectionProps = new Properties();
    connectionProps.put("user", this.userName);
    connectionProps.put("password", this.password);

    if (this.dbms.equals("mysql")) {
        conn = DriverManager.getConnection(
                   "jdbc:" + this.dbms + "://" +
                   this.serverName +
                   ":" + this.portNumber + "/",
                   connectionProps);
    } else if (this.dbms.equals("derby")) {
        conn = DriverManager.getConnection(
                   "jdbc:" + this.dbms + ":" +
                   this.dbName +
                   ";create=true",
                   connectionProps);
    }
    System.out.println("Connected to database");
    return conn;
}

The method DriverManager.getConnection establishes a database connection.方法DriverManager.getConnection建立数据库连接。This method requires a database URL, which varies depending on your DBMS.此方法需要一个数据库URL，该URL因DBMS而异。The following are some examples of database URLs:以下是一些数据库URL示例：

1. MySQL: jdbc:mysql://localhost:3306/, where localhost is the name of the server hosting your database, and 3306 is the port numberMySQL:jdbc:mysql://localhost:3306/，其中localhost是承载数据库的服务器的名称，3306是端口号

2. Java DB: jdbc:derby:testdb;create=true, where testdb is the name of the database to connect to, and create=true instructs the DBMS to create the database.javadb：jdbc:derby:testdb;create=true，其中testdb是要连接到的数据库的名称，create=true指示DBMS创建数据库。

   Note: This URL establishes a database connection with the Java DB Embedded Driver.：此URL建立与Java DB嵌入式驱动程序的数据库连接。Java DB also includes a Network Client Driver, which uses a different URL.JavaDB还包括一个网络客户端驱动程序，它使用不同的URL。

This method specifies the user name and password required to access the DBMS with a Properties object.此方法指定使用Properties对象访问DBMS所需的用户名和密码。

Note:

• Typically, in the database URL, you also specify the name of an existing database to which you want to connect.通常，在数据库URL中，还可以指定要连接到的现有数据库的名称。For example, the URL jdbc:mysql://localhost:3306/mysql represents the database URL for the MySQL database named mysql.例如，URL jdbc:mysql://localhost:3306/mysql表示名为MySQL的MySQL数据库的数据库URL。The samples in this tutorial use a URL that does not specify a specific database because the samples create a new database.本教程中的示例使用的URL不指定特定数据库，因为示例创建了一个新数据库。

• In previous versions of JDBC, to obtain a connection, you first had to initialize your JDBC driver by calling the method Class.forName.在以前版本的JDBC中，要获得连接，首先必须通过调用Class.forName方法初始化JDBC驱动程序。This methods required an object of type java.sql.Driver.此方法需要java.sql.Driver类型的对象。Each JDBC driver contains one or more classes that implements the interface java.sql.Driver.每个JDBC驱动程序都包含一个或多个实现接口java.sql.driver的类。The drivers for Java DB are org.apache.derby.jdbc.EmbeddedDriver and org.apache.derby.jdbc.ClientDriver, and the one for MySQL Connector/J is com.mysql.cj.jdbc.Driver.Java DB的驱动程序是org.apache.derby.jdbc.EmbeddedDriver和org.apache.derby.jdbc.ClientDriver，MySQL Connector/J的驱动程序是com.MySQL.cj.jdbc.Driver。See the documentation of your DBMS driver to obtain the name of the class that implements the interface java.sql.Driver.请参阅DBMS驱动程序的文档，以获取实现接口java.sql.driver的类的名称。

  Any JDBC 4.0 drivers that are found in your class path are automatically loaded.在类路径中找到的任何JDBC4.0驱动程序都会自动加载。(However, you must manually load any drivers prior to JDBC 4.0 with the method Class.forName.)（但是，您必须使用方法Class.forName手动加载JDBC 4.0之前的任何驱动程序。）

The method returns a Connection object, which represents a connection with the DBMS or a specific database.该方法返回一个Connection对象，该对象表示与DBMS或特定数据库的连接。Query the database through this object.通过此对象查询数据库。

Specifying Database Connection URLs指定数据库连接URL

A database connection URL is a string that your DBMS JDBC driver uses to connect to a database.数据库连接URL是DBMS JDBC驱动程序用于连接数据库的字符串。It can contain information such as where to search for the database, the name of the database to connect to, and configuration properties.它可以包含诸如在何处搜索数据库、要连接到的数据库的名称以及配置属性等信息。The exact syntax of a database connection URL is specified by your DBMS.数据库连接URL的确切语法由DBMS指定。

Java DB Database Connection URLsJavaDB数据库连接URL

The following is the database connection URL syntax for Java DB:以下是Java DB的数据库连接URL语法：

jdbc:derby:[subsubprotocol:][databaseName][;attribute=value]*

• subsubprotocol specifies where Java DB should search for the database, either in a directory, in memory, in a class path, or in a JAR file.指定Java DB应该在何处搜索数据库，在目录中、内存中、类路径中或JAR文件中。It is typically omitted.它通常被省略。
• databaseName is the name of the database to connect to.要连接到的数据库的名称。
• attribute=value represents an optional, semicolon-separated list of attributes.表示可选的、以分号分隔的属性列表。These attributes enable you to instruct Java DB to perform various tasks, including the following:这些属性使您能够指示Java DB执行各种任务，包括以下任务：
  • Create the database specified in the connection URL.创建连接URL中指定的数据库。
  • Encrypt the database specified in the connection URL.加密连接URL中指定的数据库。
  • Specify directories to store logging and trace information.指定用于存储日志记录和跟踪信息的目录。
  • Specify a user name and password to connect to the database.指定要连接到数据库的用户名和密码。

See Java DB Developer's Guide and Java DB Reference Manual from Java DB Technical Documentation for more information.有关更多信息，请参阅《Java DB技术文档》中的Java DB开发者指南和Java DB参考手册。

MySQL Connector/J Database URLMySQL连接器/J数据库URL

The following is the database connection URL syntax for MySQL Connector/J:以下是MySQL Connector/J的数据库连接URL语法：

jdbc:mysql://[host][,failoverhost...]
    [:port]/[database]
    [?propertyName1][=propertyValue1]
    [&propertyName2][=propertyValue2]...

• host:port is the host name and port number of the computer hosting your database.托管数据库的计算机的主机名和端口号。If not specified, the default values of host and port are 127.0.0.1 and 3306, respectively.如果未指定，主机和端口的默认值分别为127.0.0.1和3306。
• database is the name of the database to connect to. If not specified, a connection is made with no default database.要连接到的数据库的名称。如果未指定，则在没有默认数据库的情况下进行连接。
• failover is the name of a standby database (MySQL Connector/J supports failover).备用数据库的名称（MySQL Connector/J支持故障切换）。
• propertyName=propertyValue represents an optional, ampersand-separated list of properties.表示可选的、以符号和分隔的属性列表。These attributes enable you to instruct MySQL Connector/J to perform various tasks.这些属性使您能够指示MySQL Connector/J执行各种任务。

See MySQL Reference Manual for more information.有关更多信息，请参阅《MySQL参考手册》。