JDBC Summary - programming steps and principles

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JDBC summary

A, JDBC Introduction

• JDBC (Java Data Base Connectivity) API is a set of application programming interfaces for the Java language to access the database.
• Essentially, that is the agreement between the caller (programmer) and implementers (database vendors).
• jDBC implementation provided by the database vendor in the form of drivers.
• JDBC API allows developers to use pure java way to link database, and operate it.

Two, JDBC principle

Three, JDBC object introduction

Jdbc common class

The JDBC core classes have: DriverManager, Connnection, Statement and ResultSet

1, the role of the DriverManager (drive manager) has two

• Registration drive: This lets JDBC know which drive you want to use

  DriverManager.registerDriver()方法:You can understand, the registration drive for general useClass.forName()

• Gets Connection: If you can get to the Connection, then that is already connected to the database on
  getConnection()方法:

2, Connection object represents a connection and communication with the database is through the expansion of the object:

• Connection is the most important method used to obtain a Statement object
  Statement statement = connection.createStatement();
  Code:

3, Statement is used to send SQL statements to the database, so the database will be sent by the implementation of SQL statement:

Commonly used methods Statement

• int executeUpdate(String sql)：执行更新操作（insert，update，delete等）
  • Perform update operations that insert, update, delete statement
  • You can also perform create table, alter table, drop table and other statements, but rarely used
  • Returns the number of rows is operating
• ResultSet executeQuery(String sql)：执行查询操作，数据库在执行查询后会把查询结果ResultSet返回
  • Execute the query operation, namely the select statement
  • Back ResultSet, i.e. the result sets
• boolean execute();
  • Can be used to perform all the sql statement executeUpdate and executeQuery two methods can be performed, i.e., you can perform all the sql statement CRUD
  • This method returns a boolean indicating whether the SQL statement has a result set
  • If the update statement with this method, you have to call int
    getUpdateCount () to get the number of rows affected insert, update, delete statement
  • If you use this method to execute a query statement, but also calls ResultSet getResult () to get the select statement query results

Three kinds of Statement objects

• Statement 对象
  • Role: to perform simple SQL statement with no parameters
  • Features: each SQL statement is executed, the database must execute compiled SQL statement, the best situation is performed only once for a query and returns the results,
  • More efficient than PreparedStatement
• PreparedStatement
  • Role: to perform with or without IN parameters of pre-compiled SQL statement
  • Features:
    • ① is precompiled, in the implementation of variable parameters of a SQL statement, more efficient than Statement, as a pre-compiled SQL DBMS, of course, many times more than a compiled SQL higher efficiency
    • ② safety, prevent SQL injection and other issues
    • ③ For a statement executed repeatedly, it is more efficient, and in this case also more suitable for use batch
    • ④ code readability and maintainability good
• CallableStatement
  • Role: A call to a database stored procedure for execution
  • Features: it provides support for input and output parameters
  • This interface supports having input and output parameters of the interfaces provided PreparedStatment

Code:

4, ResultSet object represents a query result set only perform the operation will be after generating a query result set

• The result set is a two-dimensional form, there are row has columns.
• To set the operation result using the "cursor row" inside ResultSet, and acquiring data on each column of the current row
• boolean next()；是行光标移动到下一行，并返回移动后的行是否存在
• getXXX(int index)；获取指针所指向的当前行数据
• colose()；释放资源

Four, JDBC programming steps

Need to introduce mysql-connector-java-5.1.39-bin.jar kit.

1, mysql database-driven load

  /**
     * 所有的java.sql.Driver实现类，都提供了static块，
     * 块内的代码就是把自己注册到DriverManager中
     */
 Class.forName("com.mysql.jdbc.Driver");   //加载驱动类（注册驱动）
    /*等价于*/
 com.mysql.jdbc.Driver driver = new com.mysql.jdbc.Driver();   //注册驱动
 DriverManager.registerDriver(driver);

Usually with the Class.forName () method of driving load.

2, Get Link

//设置参数
String url = "jdbc:mysql://localhost:3306/mybase";
String username = "root";
String password = "123";

//使用url，username，password，得到连接对象
Connection connection = DriverManager.getConnection(url,username,password);

3, get Statement

(1) Statement object to obtain

Statement stm = conn.createStatement();

(2) to obtain the object preparedStatement

String sql = "select * from emp where job=?";
pstm = conn.prepareStatement(sql);		//创建sql半成品
pstm.setString(1,"clerk");				//参数绑定

The value part of the SQL statement changes with placeholders obtaining PreparedStatement object through the connection, create: ① create sql semi-finished products? instead.
② parameter binding, that is? Assignment (set[type](1,2)方法) The first parameter represents the position from the beginning;? The second argument is a specific value.

4, execute SQL statements

(1) If the Statement object query, use ResultSet rs = stm.executeQuery(sql);
(2) If the object is preparedStatement query, use ResultSet rs = pstm.executeQuery();
(3) If there are a lot of sql statement needs to be performed, it is necessary to use批处理。

5, the result set (query needs)

while(rs.next()){
	 String number = rs.getString(1);		//通过列编号来获取该列的值 
    String name = rs.getString("name");  	//通过列名称来获取该列的值
    int age = rs.getInt(3);
    String gender = rs.getString(4);
    System.out.println(number + "," + name + "," + age + "," + gender);
}

6, the close link

// 倒关（先得到的资源后关闭，后得到的资源先关闭）
rs.close();
stm.close();
conn.close();   //这个必须要关

V. specification code sample

1, create a connection to the database Statement

import java.sql.*;

public class testStatement {
	public static void main(String[] args) {
		Connection conn = null;
		Statement stm = null;
		ResultSet rs = null;
		
		try {
			//1、加载驱动
			Class.forName("com.mysql.jdbc.Driver");
			//2、获取连接
			String url = "jdbc:mysql://localhost:3306/mybase?serverTimezone=UTC";
			String user = "root";
			String password = "159357";
			conn = DriverManager.getConnection(url, user, password);
			//3、创建Statement对象
			stm = conn.createStatement();
			//4、执行sql语句
			//查询数据库statement.executeQuery(查询sql)
			String sql = "select * from emp";
			rs = stm.executeQuery(sql);
			
			//修改操作数据库 statement.executeUpdate(增删改sql)
			/*String sql = "insert into emp(ename,job,deptno) values('小龙人','manager',10)";
			String sql = "delete from emp where ename='小龙人'";
			String sql = "update emp set job='leader' where ename='张伟'";
			int lines = stm.executeUpdate(sql);
			System.out.println("影响的行数"+lines);
			*/
			//5、处理结果集
			while(rs.next()){
				//int empno = rs.getInt(1);
				int empno = rs.getInt("empno");
				String ename = rs.getString(2);
				String job = rs.getString(3);
				int mgr = rs.getInt(4);
				Date hiredate = rs.getDate(5);
				double  sal= rs.getDouble(6);
				//double comm = rs.getDouble(7);
				double comm = rs.getDouble("comm");
				int deptno = rs.getInt(8);
				System.out.println(empno+" "+ename+" "+job+" "+mgr
				+" "+hiredate+" "+sal+" "+comm+" "+deptno);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}finally{
			//6.关闭链接
            if(resultSet != null)
            {
                resultSet.close();
            }
            if(statement != null)
            {
                statement.close();
            }
            if(connection != null)
            {
                connection.close();
            }
	}
}

3. Create a database connection preparedStatement

pstm build dynamic sql
resolve Sql injection vulnerabilities, can be performed using sql PreparedStatement. It is
a sub-step of using the interface Statemnet three steps:

(1) Create: PreparedStatement object obtained through links

	String sql="select * from user_luxw where username=? Andpassowrd=?";
	PreoparedStatment pstm = conn.prepareStatement(sql);

创建时，将SQL语句中取值发生变化的部分用占位符(?)替代。

(2) to? Assignment (also called parameter binding)

/*使用set[Type]方法给？赋值。其中Type表示？表示？位置的数据类型。第一个参数代表问号
位置从1开始;第二个参数是具体取值，比如：*/
pstm.setString(1,username);
pstm.setString(2,password);

(3) the implementation of SQL

	pstm.executeQuery();
	pstm.executeUpdate();	//执行更新时使用

此时JDBC将所有？对应的参数发送至数据库服务器，调用在共享池中由第一步创建的预编译的SQL并执行

Complete code:

package jdbc;

import java.sql.*;
import java.util.Date;

/**
 - 类说明:
 - 		JDBC创建PreparedStatement对象连接数据库
 */
public class testPreparedStatement {
	public static void main(String[] args) {
		Connection conn = null;
		PreparedStatement pstm = null;
		ResultSet rs = null;
		try {
			// 1.加载驱动
			Class.forName("com.mysql.jdbc.Driver");
			// 2.获取连接
			String url = "jdbc:mysql://localhost:3306/mybase?useUnicode=true&characterEncoding=utf-8";
			String user = "root";
			String password = "123";
			conn = DriverManager.getConnection(url, user, password);
			// 3.创建PreparedStatement,预编译sql语句
			String sql = "select * from emp where job=?";
			pstm = conn.prepareStatement(sql);//创建sql半成品
			pstm.setString(1,"clerk");//参数绑定
			//4.执行sql语句
			rs = pstm.executeQuery();
			//5.处理结果集
			while(rs.next()){
				int empno = rs.getInt("empno");
				String ename = rs.getString("ename");
				String job = rs.getString(3);
				int mgr = rs.getInt("mgr");
				Date hiredate = rs.getDate(5);
				double sal = rs.getDouble("sal");
				double comm = rs.getDouble("commit");
				int deptno = rs.getInt(8);
				System.out.println(empno+" "+ename+" "+job+" "+mgr+" "+hiredate+" "+sal+" "+comm+" "+deptno);
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			// 6.关闭连接/释放资源
			try {
				rs.close();
				pstm.close();
				conn.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}
}

4, Statement and compare preparedStatement

• Execution statement: Create stm Object -> compile -> execute (execute a sql statement 10 seconds).
• Execution of PreparedStatement:
  Create Object pstm (sql semi) -> set value -> performing data transmission (sql statement performs a 12 seconds, and the values set sql but requires only 2 seconds)

5, Batch

(1) Statement completed batch

• Add a batch using the Statement object to execute SQL statements
• Executing batch SQL statement:Statement.executeBatch();
• Clear batch commands:Statement.clearbatch();

Advantages: you can send a number of different SQL statements to the database.
Drawback: SQL statement is not pre-compiled.
When sending multiple statements to the same database, but only parameters different SQL statements, to be repeated on many write SQL statements.

Complete code:

import java.sql.*;

/*
 * statement批处理
 */
public class testStatementBatch {
	public static void main(String[] args) throws ClassNotFoundException, SQLException {
		//加载链接
		Class.forName("com.mysql.jdbc.Driver");
		//获取链接
		Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mybase?serverTimezone=UTC", "root", "159357");
		//创建Statement
		Statement stm = conn.createStatement();
		String sql = "insert into emp(ename,job,deptno) values('小龙人','clerk',20)";
		String sql1 = "insert into emp(ename,job,deptno) values('美人鱼','leader',10)";
		String sql2 = "update emp set ename='小龙人1' where ename='小龙人'";
		//添加批处理
		stm.addBatch(sql);
		stm.addBatch(sql1);
		stm.addBatch(sql2);
		//执行批处理ִ
		stm.executeBatch();
		//清除批处理
		stm.clearBatch();
		//释放资源
		stm.close();
		conn.close();
	}
}

(2) PreoparedStatment batch

• Using PrepareStatement.addBatch()batch processing

Advantages: transmission is that the pre-compiled SQL statements, high efficiency
disadvantages: SQL statement can only be applied in the same, but different batch parameters, thus often used for this form of batch bulk insert a table in the same data, or data batch updates the table.

import java.sql.*;

/*
 * prepareStatement批处理
 */
public class testPreparedStatemnetBatch {
	public static void main(String[] args) throws Exception {
		//加载驱动
		Class.forName("com.mysql.jdbc.Driver");
		//获取链接
		Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mybase?serverTimezone=UTC", "root", "159357");
		String sql="insert into emp(empno,ename,deptno) values(?,?,?)";
		//创建preparedStatemet
		PreparedStatement pstm = conn.prepareStatement(sql);
		//pstm绑定数据
		for(int i=3008;i<4008;i++){
			pstm.setInt(1, i);
			pstm.setString(2, "李白"+i);
			pstm.setInt(3,20);
			//添加批处理
			pstm.addBatch();
			//ִ执行批处理
			if(i%100==0){
				pstm.executeBatch();
				pstm.clearBatch();
			}
		}
		//执行批处理
		pstm.executeBatch();
		//释放资源
		pstm.close();
		conn.close();
	}
}