JDBC入门学习

Posted 2020-07-19 Emma

Introduction

What\'s JDBC

JDBC stands for Java Database Connectivity, which is a standard Java API for database-independent connectivity between the Java programming language and a wide range of databases.

JDBC library (includes APIs)的主要用途包括

• Making a connection to a database. 连接数据库

• Creating SQL or mysql statements. 创建SQL或者MySQL语句

• Executing SQL or MySQL queries in the database. 执行SQL或者MySQL查询

• Viewing & Modifying the resulting records. 查看或者修改结果

JDBC架构

JDBC支持两层或者三层处理逻辑。但是一般，包括两层结构

• JDBC API: This provides the application-to-JDBC Manager connection.

• JDBC Driver API: This supports the JDBC Manager-to-Driver Connection.

JDBC drivers实现了JDBC APIs定义的接口。

JDBC连接

连接JDBC通常有四个简单的步骤 

• Import JDBC Packages: Add import statements to your Java program to import required classes in your Java code.

• Register JDBC Driver: This step causes the JVM to load the desired driver implementation into memory so it can fulfill your JDBC requests.

• Database URL Formulation: This is to create a properly formatted address that points to the database to which you wish to connect.

• Create Connection Object: Finally, code a call to the DriverManagerobject\'s getConnection( ) method to establish actual database connection.

注册JDBC driver

注册JDBC driver有两种方法：

Approach 1: Class.forName() 自动将driver相关class加载到内存

try {
   Class.forName("oracle.jdbc.driver.OracleDriver");
}
catch(ClassNotFoundException ex) {
   System.out.println("Error: unable to load driver class!");
   System.exit(1);
}

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Approach 2: DriverManager.registerDriver() 如果使用的是 non-JDK compliant JVM

try {
   Driver myDriver = new oracle.jdbc.driver.OracleDriver();
   DriverManager.registerDriver( myDriver );
}
catch(ClassNotFoundException ex) {
   System.out.println("Error: unable to load driver class!");
   System.exit(1);
}

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Database URL formulation

加载完driver之后，可以用DriverManager.getConnection()建立连接。

下面是常用数据库与connection URL的映射表

RDBMS	JDBC driver name	URL format
MySQL	com.mysql.jdbc.Driver	jdbc:mysql://hostname/ databaseName
ORACLE	oracle.jdbc.driver.OracleDriver	jdbc:oracle:thin:@hostname:port Number:databaseName
DB2	COM.ibm.db2.jdbc.net.DB2Driver	jdbc:db2:hostname:port Number/databaseName
Sybase	com.sybase.jdbc.SybDriver	jdbc:sybase:Tds:hostname: port Number/databaseName

JDBC statement，PreparedStatement & CallableStatement

根据不同的需用，可以选择不同的statement接口。

Interfaces	Recommended Use
Statement	Use for general-purpose access to your database. Useful when you are using static SQL statements at runtime. The Statement interface cannot accept parameters.
PreparedStatement	Use when you plan to use the SQL statements many times. The PreparedStatement interface accepts input parameters at runtime.
CallableStatement	Use when you want to access the database stored procedures. The CallableStatement interface can also accept runtime input parameters.

Statement

创建statement

Statement stmt = null;
try {
   stmt = conn.createStatement( );
   . . .
}
catch (SQLException e) {
   . . .
}
finally {
   . . .
}

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执行statement

创建完statement object之后，可以用来执行SQL语句

• boolean execute (String SQL): Returns a boolean value of true if a ResultSet object can be retrieved; otherwise, it returns false. Use this method to execute SQL DDL statements or when you need to use truly dynamic SQL.

• int executeUpdate (String SQL): Returns the number of rows affected by the execution of the SQL statement. Use this method to execute SQL statements for which you expect to get a number of rows affected - for example, an INSERT, UPDATE, or DELETE statement.

• ResultSet executeQuery (String SQL): Returns a ResultSet object. Use this method when you expect to get a result set, as you would with a SELECT statement.

关闭statement

如果close connection节省数据库资源一样，close statement可以确保资源的合理回收。

Statement stmt = null;
try {
   stmt = conn.createStatement( );
   . . .
}
catch (SQLException e) {
   . . .
}
finally {
   stmt.close();
}

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JDBC 批处理

批处理(batch processing)允许一次执行多条SQL语句。由于JDBC drivers并没有要求实现这个功能，因此使用前先用 DatabaseMetaData.supportsBatchUpdates() 检测目标数据库是否支持批处理。

Statement对象的批处理

• Create a Statement object using either createStatement() methods.

• Set auto-commit to false using setAutoCommit().

• Add as many as SQL statements you like into batch using addBatch()method on created statement object.

• Execute all the SQL statements using executeBatch() method on created statement object.

• Finally, commit all the changes using commit() method.

// Create statement object
Statement stmt = conn.createStatement();

// Set auto-commit to false
conn.setAutoCommit(false);

// Create SQL statement
String SQL = "INSERT INTO Employees (id, first, last, age) " +
             "VALUES(200,\'Zia\', \'Ali\', 30)";
// Add above SQL statement in the batch.
stmt.addBatch(SQL);

// Create one more SQL statement
String SQL = "INSERT INTO Employees (id, first, last, age) " +
             "VALUES(201,\'Raj\', \'Kumar\', 35)";
// Add above SQL statement in the batch.
stmt.addBatch(SQL);

// Create one more SQL statement
String SQL = "UPDATE Employees SET age = 35 " +
             "WHERE id = 100";
// Add above SQL statement in the batch.
stmt.addBatch(SQL);

// Create an int[] to hold returned values
int[] count = stmt.executeBatch();

//Explicitly commit statements to apply changes
conn.commit();

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PreparedStatement对象的批处理

// Create SQL statement
String SQL = "INSERT INTO Employees (id, first, last, age) " +
             "VALUES(?, ?, ?, ?)";

// Create PrepareStatement object
PreparedStatemen pstmt = conn.prepareStatement(SQL);

//Set auto-commit to false
conn.setAutoCommit(false);

// Set the variables
pstmt.setInt( 1, 400 );
pstmt.setString( 2, "Pappu" );
pstmt.setString( 3, "Singh" );
pstmt.setInt( 4, 33 );
// Add it to the batch
pstmt.addBatch();

// Set the variables
pstmt.setInt( 1, 401 );
pstmt.setString( 2, "Pawan" );
pstmt.setString( 3, "Singh" );
pstmt.setInt( 4, 31 );
// Add it to the batch
pstmt.addBatch();

//add more batches
.
.
.
.
//Create an int[] to hold returned values
int[] count = stmt.executeBatch();

//Explicitly commit statements to apply changes
conn.commit();

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 References

http://www.tutorialspoint.com/jdbc/jdbc-where-clause.htm

http://stackoverflow.com/questions/2839321/connect-java-to-a-mysql-database