Oracle +JDBC

JDBC

JDBC brief introduction

JDBC（Java Data Base Connectivity,java Database connection ） It's one for execution SQL Of the statement Java API, It can provide unified access for a variety of relational databases , It's used by a group Java Language written classes and interfaces .JDBC It provides a benchmark , From this, you can build more advanced tools and interfaces , Enable database developers to write database applications .

After we install the database , Our application can't use the database directly , Must pass the corresponding database driver , Dealing with database through driver . In fact, it is the database manufacturer's JDBC Interface implementation , to Connection Implementation class jar file .

JDBC + Oracle + Eclipse

brief introduction

We installed XE There is one in the version Oracle The official JDBC jar package , Location is ：app\oracle\product\11.2.0\server\jdbc\lib

There are three

• ojdbc5： And jdk1.5 Corresponding
• ojdbc6： And jdk1.6 Corresponding
• ojdbc6_g：jdk1.6 Compiled version of

We can choose any one , file jdk yes 11 ,Oracle Yes, I have uploaded resources before 11g XE Version of

external JAR Package loaded into our project

• In our Java Create a folder under the project Put these exteriors jar package The general file name is lib【 And src At the same level 】

• Then right-click the project name , choice Build Path, Choose... As shown in the picture
  

• choice labiries – 》 ModulePath — 》 Add JARS Select the... You created lib Below jar package —》 application OK to close
  

• Then you can see lib There is a under the same level directory Referenced Libraries【 Application Library 】 This way jdbc Introduced into your library

  

Cognitive structure

This Jar Under the package are all classes related to databases , Interfaces, etc. . It and Java.sql as well as Javax.sql The three work together to operate the database , This JDBC It's just one. java Middleware for program operation database , It's also called JDBC drive

Java Program aid JDBC Connect to database

Java API

JDBC API Mainly located in JDK Medium java.sql In bag （ The expanded content is located in javax.sql In bag ）, It mainly includes （ Italics represent interfaces , The driver provider is needed to implement ）：

• DriverManager： Responsible for loading various drivers （Driver）, And according to different requests , Return the corresponding database connection to the caller （Connection）.
• Driver： The driver , Will load itself into DriverManager In the middle , And process the corresponding request and return the corresponding database connection （Connection）.
• Connection： Database connection , Responsible for communication with database ,SQL Execution and transaction processing are all in a specific Connection In the environment . Can be generated to perform SQL Of Statement.
• Statement： To carry out SQL Query and update （ For static SQL Statement and single execution ）.
• PreparedStatement： Used to execute... With dynamic parameters SQL Query and update （ Compile... On the server side , Allow repeat execution to improve efficiency ）.
• CallableStatement： Used to call stored procedure .
• SQLException： Represents the establishment and closure of a database connection and SQL Exception occurred during statement execution （ It's a mistake ）.

step

1. Load database driver

In programming, you should connect to the database , You must first load a specific vendor's database driver , Different databases have different loading methods . Such as ：

• load MySql drive ：Class.forName(“com.mysql.jdbc.Driver”);

• load Oracle drive ：Class.forName(“oracle.jdbc.driver.OracleDriver”);

2. Create database connection ：Connection Interface

This interface is used to create database connection

Connection conn = DriverManager.getConnection(String url,String username,String userpasswd);

• DriverManager Class getConnection() Will return a Connection Database connection object , Its parameters are not fixed , The most commonly used d These are the three
• url： The address of the database service is usually written in a fixed way
  • Oracle：jdbc:oracle:thin:@ip Address : Port number （1521）:XE
  • MySql：jdbc:mysql://ip Address : Port number （3306）/ database 【 As if 5.7 after 8.0 You need to write the time zone 】
    • jdbc:mysql://localhost:3306/test?&useSSL=false&serverTimezone=UTC
  • SqlServer：jdbc:microsoft:sqlserver://ip Address : Port number ;DatabaseName = databasename
• username： Connected database users
• userpasswd： Database user password

3. establish sql actuator ：Statement Interface

Statement st = conn.createStatement();

4. perform sql

5. Process the returned result set or other operations

There are two common ways ,excuteQuery() and excuteUpdata() , The first return result set , It uses query sql sentence , The second is to increase 、 Delete 、 Change UPDATE statement of , Return integer data , Greater than 0 Then the execution is successful , Otherwise failure .

Generally, if it is a query, the result set is returned ResultSet, More on that later . There is one next() Method , The return value is Boolean type , Use it to get data .

6. Release database connection resources

When releasing the database connection, write in the order of first entering the stack and then exiting the stack , Then every time it is closed, there will be exceptions , And we have to make non empty judgments , Otherwise, it is easy to report null pointer abnormal errors .

give an example

package com.bigdata.jdbcdemo.oracle;
import java.sql.*;
public class demoSelect {
    
	public static void main(String[] args) {
    
		/** *  The load driver  *  Create connection  *  establish Statement sql Perform object  *  perform sql *  Processing return results  *  Release database resources  */
		//  First of all   It's good to close it at last 
		Connection conn = null;
		Statement ste = null;
		ResultSet rs = null;
		try {
    
			//  Class cannot find exception 
			Class.forName("oracle.jdbc.OracleDriver");
			// sql abnormal 
			conn = DriverManager.getConnection("jdbc:oracle:thin:@127.0.0.1:1521:XE", "SCOTT", "lzyft1030");
			ste = conn.createStatement();
			String sql = "SELECT ENAME,JOB,SAL FROM EMP";
			rs = ste.executeQuery(sql);
			System.out.println(" full name \t Work \t Wages ");
			while (rs.next()) {
    
				System.out.println(rs.getString("ENAME")+"\t"+rs.getString("JOB")+"\t"+rs.getInt(3));
			}
		} catch (ClassNotFoundException | SQLException e) {
    
			
			e.printStackTrace();
		} finally {
    
			//  Do not do null Judge   prevent NPE【NullPointerException】
				try {
    
					if (ste != null) {
    
						ste.close();
					}
					if (conn != null) {
    
						conn.close();
					}
				} catch (SQLException e) {
    
					e.printStackTrace();
				}
		}
	}
}

Common interfaces

Connection Interface

Class.forName("oracle.jdbc.OracleDriver");
Connection conn = DriverManager.getConnection(...);

Statement Interface

For execution static SQL Statement and returns the object for which it generated the result .

Three Statement class ：

Statement：

from createStatement establish , For sending simple SQL sentence （ No parameters Sql, You can do it Sql Combine ）.

Statement st = conn.createStatement();
String sql = "delete from tablename where id = "5" + "..." "; //  No placeholders  ？ Can be combined   So the security is not high   String combination   Change the string online or follow it with something else   It breaks down directly 
int code = st.excuteUpdate(sql);
ResultSet rst = st.excuteQuery(sql);

PreparedStatement ：

Inherited from Statement Interface , from prepareStatement establish , Used to send messages containing one or more parameters 【 Place holder 】 Of SQL sentence .PreparedStatement Object ratio Statement Objects are more efficient , And it can prevent SQL Inject , So we usually use PreparedStatement.

【 Notice the difference between the interface and the creation method ：PreparedStatement pst = conn.prepareStatement(sql);】

CallableStatement：

Inherited from PreparedStatement Interface , By way prepareCall establish , For calling stored procedures .

Commonly used Statement Method ：

• execute(String sql): Run statement , Returns whether there is a result set
• executeQuery(String sql)： function select sentence , return ResultSet Result set .
• executeUpdate(String sql)： function insert/update/delete operation , Returns the number of updated rows .
• addBatch(String sql) ： Put more than one sql Statement in a batch .
• executeBatch()： Send a batch of sql Statement execution .

ResultSet Interface

ResultSet Provides a way to retrieve different types of fields , Commonly used ：

• getString(int index)、getString(String columnName)： Get in the database yes varchar、char Data objects of the same type .
• getFloat(int index)、getFloat(String columnName)： Get in the database yes Float Type of data object .
• getDate(int index)、getDate(String columnName)： Get in the database yes Date Data of type .
• getBoolean(int index)、getBoolean(String columnName)： Get data of boolean type in the database
• getObject(int index)、getObject(String columnName)： Get any type of data in the database .

ResultSet It also provides a way to scroll the result set ：

• next()： Move to next line , Returns a Boolean value
• previous()： Move to previous line
• absolute(int row)： Move to specified row
• beforeFirst()： Move resultSet Foremost .
• afterLast() ： Move to resultSet At the back of .

ResultSetMetaData

Metadata used to return the result set ,ResultSet Subclasses of , General method prototypes are ResultSet Of , When using, you can check API To use the

give an example

Tools for connecting and closing databases

package com.bigdata.jdbcdemo.oracle;

import java.sql.*;

public class DBConnection {
    
	private static Connection conn = null;
	
	/** *  establish Oracle  Database connection  */
	public static Connection getConnectOracle(){
    
		try {
    
			Class.forName("oracle.jdbc.OracleDriver");
			conn = DriverManager.getConnection("jdbc:oracle:thin:@127.0.0.1:1521:XE","SCOTT","123");
		} catch (ClassNotFoundException | SQLException e) {
    
			e.printStackTrace();
		}
		return conn;
	}
	
	/** *  Release resources  */
	public static void closeAll(ResultSet rst, PreparedStatement pst, Connection conn) {
    
		try {
    
            if (rst != null) {
    
                rst.close();
            }
            if (pst != null) {
    
                pst.close();
            }
            if (conn != null) {
    
                conn.close();
            }
        } catch (SQLException e) {
    
            e.printStackTrace();
        }
	}
}

Specific exercises

package com.bigdata.jdbcdemo.oracle;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;

public class PreparedStatementTest {

	public static void main(String[] args) {
		PreparedStatement pst = null;
		ResultSet  rst = null;
		ResultSetMetaData rstmd = null;
		Connection conn = DBConnection.getConnectOracle();
		String sql = "select ename,job,sal from emp where deptno = ?";
		try {
			pst = conn.prepareStatement(sql);
			pst.setInt(1, 10);
			rst = pst.executeQuery();
			while (rst.next()) {
				System.out.println(rst.getString(1)+"\t"+rst.getString("JOB")+"\t"+rst.getInt(3));
			}
			rstmd = rst.getMetaData();
			System.out.println(" Number of columns ："+rstmd.getColumnCount());
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			DBConnection.closeAll(rst, pst, conn);
		}
	}
}

Sql To Java Data type mapping

SQL type	Java type
CHAR	java.lang.String
VARCHAR	java.lang.String
LONGVARCHAR	java.lang.String
NUMERIC	java.math.BigDecimal
DECIMAL	java.math.BigDecimal
BIT	boolean
TINYINT	byte
SMALLINT	short
INTEGER	int
BIGINT	long
REAL	float
FLOAT	double
DOUBLE	double
BINARY	byte[]
VARBINARY	byte[]
LONGVARBINARY	byte[]
DATE	java.sql.Date
TIME	java.sql.Time
TIMESTAMP	java.sql.Timestamp
BLOB	java.sql.Blob
CLOB	java.sql.Clob
Array	java.sql.Array
REF	java.sql.Ref
Struct	java.sql.Struct

notes ： This type matching is not a mandatory standard , specific JDBC Vendors may change this type of matching . for example Oracle Medium DATE The type is including hours, minutes and seconds , and java.sql.Date Only support mm / DD / yy .

Date transformation

• java.sql.Date
  • Date d = new Date(1900 + year, 1+month, day);
  • int Parameters of type
  • PreParedStatement() Medium sql Of Date type Not directly to_date() You need to use this Date Object to pass in
• Oracle The type of Date
  • to_date( Date string ,' Format ');： By format String to date
  • to_char(date,' Format ');： Date to string in format
  • add_month(date, Positive and negative numbers ); ： Add date month
  • last_day(date); ： The last item of the date
  • date + interval ‘ Positive and negative numbers ’ year/month( Number of digits , Default 2 position )： Press the following... For the date year or month Plus and minus numbers 【±】

Connect to the database with the configuration file

Create a file

create a file , It is best to put it under the same level directory of the class connected to the database , General file naming ：date.properties , The format should be fixed

classDriver = oracle.jdbc.OracleDriver
url = jdbc:oracle:thin:@127.0.0.1:1521:XE
username = scott
userpasswd = 123

Create a class

java.util Below is a set of key value pairs ,Hashtable Subclasses of Preperties

use InputStream Object to read file data

InputStream is =  The name of the class .class.getResourceAsStream("data.properties");
Prepareties p = new Prepareties();
p.load(is);
p.getProperty(key);//  Get key value 

Sample code

package com.bigdata.jdbcdemo.oracle;

import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

public class DBConnectByFile {
    
    //  Input stream reads configuration file   Get resource flow with current class   The parameter is the relative path of the configuration file 
    private static InputStream is = DBConnectByFile.class.getResourceAsStream("oracleConn.properties");
    private static Properties properties = new Properties();

    /** * @return  Return drive  */
    public static String getDriverClass() {
    
        try {
    
            properties.load(is);
        } catch (IOException e) {
    
            e.printStackTrace();
        }
        return properties.getProperty("classDriver");
    }

    /** * @return  return url */
    public static String getUrl() {
    
        try {
    
            properties.load(is);
        } catch (IOException e) {
    
            e.printStackTrace();
        }
        return properties.getProperty("url");
    }

    /** * @return username */
    public static String getUserName() {
    
        try {
    
            properties.load(is);
        } catch (IOException e) {
    
            e.printStackTrace();
        }
        return properties.getProperty("username");
    }

    /** * @return password */
    public static String getPassword() {
    
        try {
    
            properties.load(is);
        } catch (IOException e) {
    
            e.printStackTrace();
        }
        return properties.getProperty("password");
    }

    public static Connection getConnection () {
    
        Connection conn = null;
        try {
    
            Class.forName(getDriverClass());
            conn = DriverManager.getConnection(getUrl(), getUserName(), getPassword());
        } catch (ClassNotFoundException | SQLException e) {
    
            e.printStackTrace();
        }
        return conn;
    }

    public static void closeAll(ResultSet rst, PreparedStatement pst, Connection conn) {
    

            try {
    
                if (rst != null) {
    
                    rst.close();
                }
                if (pst != null) {
    
                    pst.close();
                }
                if (conn != null) {
    
                    conn.close();
                }
            } catch (SQLException e) {
    
                e.printStackTrace();
            }

    }
// public static void main(String[] args) {
    
// Connection conn = getConnection();
// System.out.println(conn != null);
// }
}

 rst.close();
            }
            if (pst != null) {
                pst.close();
            }
            if (conn != null) {
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }

}

// public static void main(String[] args) {
// Connection conn = getConnection();
// System.out.println(conn != null);
// }
}