【JDBC】——【大文本、二进制、批处理、获取自动生成主键、事务、事务的隔离级别】

1、大本文数据类型

statement.setCharacterStream


resultSet.getCharacterStream


package com.xiaozhi.clob.and.blob;

import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.Reader;
import java.net.URL;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

import com.xiaozhi.uitls.JdbcUtil;

//大文本数据的存取
/*
create database testdatabase;
use testdatabase;
create table clobtable(
id int primary key auto_increment,
content MEDIUMTEXT
);
*/
public class ClobTest
{
public static void main(String[] args)
{
saveClob();
}

public static void saveDisk()
{
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
try{
connection = JdbcUtil.getConnection();
String sql = "select content from clobtable where id=?";
statement = connection.prepareStatement(sql);
statement.setInt(1, 1);
resultSet = statement.executeQuery();

if(resultSet.next()){
Reader reader = resultSet.getCharacterStream("content");
//写到D:盘上
FileWriter out = new FileWriter("D:/man.txt");
char buf[] = new char[1024];
int len = -1;
while((len=reader.read(buf))!=-1){
out.write(buf, 0, len);
}
reader.close();
out.close();
}
}catch(Exception e){
e.printStackTrace();
}finally{
JdbcUtil.release(connection, statement, resultSet);
}
}

public static void saveClob()
{
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
try
{
connection = JdbcUtil.getConnection();
String sql = "insert into clobtable(content) values(?)";
statement = connection.prepareStatement(sql);

URL url=ClobTest.class.getClassLoader().getResource("man.txt");
String filePath=url.getPath();
File file=new File(filePath);

statement.setCharacterStream(1,new FileReader(file),(int)file.length());//要使用int类型
int num=statement.executeUpdate();

if(num>0)
System.out.println("添加成功！");
} catch (Exception e)
{
throw new RuntimeException(e);
} finally
{
JdbcUtil.release(connection, statement, resultSet);
}
}
}

2、二进制数据类型

statement.setBinaryStream


resultSet.getBinaryStream


package com.xiaozhi.clob.and.blob;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.URL;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

import com.xiaozhi.uitls.JdbcUtil;

/*大二进制数据的存取
use testdatabase;
create table blobtable(
id int primary key auto_increment,
content MEDIUMBLOB
);
*/

public class BlobTest
{
public static void main(String[] args)
{
saveBlob();
}

public static void saveDisk()
{
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
try{
connection = JdbcUtil.getConnection();
String sql = "select content from blobtable where id=?";
statement = connection.prepareStatement(sql);
statement.setInt(1, 1);
resultSet=statement.executeQuery();

while(resultSet.next()){
InputStream in = resultSet.getBinaryStream("content");
//写到D:盘上
FileOutputStream out = new FileOutputStream("D:/1.jpg");
byte buf[] = new byte[1024];
int len = -1;
while((len=in.read(buf))!=-1){
out.write(buf, 0, len);
}
in.close();
out.close();
}
}catch(Exception e){
e.printStackTrace();
}finally{
JdbcUtil.release(connection, statement, resultSet);
}
}

public static void saveBlob()
{
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
try
{
connection = JdbcUtil.getConnection();
String sql = "insert into blobtable(content) values(?)";
statement = connection.prepareStatement(sql);

URL url=ClobTest.class.getClassLoader().getResource("1.jpg");
String filePath=url.getPath();
File file=new File(filePath);

statement.setBinaryStream(1,new FileInputStream(file),(int)file.length());//要使用int类型
int num=statement.executeUpdate();

if(num>0)
System.out.println("添加成功！");
} catch (Exception e)
{
throw new RuntimeException(e);
} finally
{
JdbcUtil.release(connection, statement, resultSet);
}
}
}


3、批处理

statement.addBatch(sql1);


statement.executeBatch();


statement.clearBatch();

package com.xiaozhi.clob.and.blob;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;

import com.xiaozhi.uitls.JdbcUtil;

/*批处理
use testdatabase;
create table batchtable(
name varchar(20)
);
*/
public class BatchTest
{

public static void main(String[] args)
{
test3();
}

private static void test3(){
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
long time = System.currentTimeMillis();
try{
connection = JdbcUtil.getConnection();
String sql = "insert into batchtable (name) values(?)";
statement = connection.prepareStatement(sql);

for(int i=1;i<=1000009;i++){
statement.setString(1, "a"+i);
statement.addBatch();
if(i%1000==0){
statement.executeBatch();//list
statement.clearBatch();//清空
}
}
statement.executeBatch();
}catch(Exception e){
e.printStackTrace();
}finally{
JdbcUtil.release(connection, statement, resultSet);
}
System.out.println("用时："+(System.currentTimeMillis()-time)/1000+"秒");
}

private static void test2(){
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
try{
connection = JdbcUtil.getConnection();
String sql = "insert into batchtable (name) values(?)";
statement = connection.prepareStatement(sql);

for(int i=1;i<=1000;i++){
statement.setString(1, "a"+i);
statement.addBatch();
}
statement.executeBatch();

}catch(Exception e){
e.printStackTrace();
}finally{
JdbcUtil.release(connection, statement, resultSet);
}
}

//利用Statement批量发送处理语句：多条
private static void test1(){
Connection connection = null;
Statement statement = null;
ResultSet resultSet = null;
try{
connection = JdbcUtil.getConnection();
statement = connection.createStatement();

String sql1 = "insert into batchtable(name) values('a')";
String sql2 = "insert into batchtable(name) values('b')";
String sql3 = "delete from batchtable where name='a'";

statement.addBatch(sql1);//List
statement.addBatch(sql2);
statement.addBatch(sql3);

statement.executeBatch();//执行批处理

}catch(Exception e){
e.printStackTrace();
}finally{
JdbcUtil.release(connection, statement, resultSet);
}
}
}

采用Statement.addBatch(sql)方式实现批处理：

优点：可以向数据库发送多条不同的ＳＱＬ语句。

缺点：

SQL语句没有预编译。

当向数据库发送多条语句相同，但仅参数不同的SQL语句时，需重复写上很多条SQL语句。例如：
Insert into user(name,password) values(‘aa’,’111’);
Insert into user(name,password) values(‘bb’,’222’);
Insert into user(name,password) values(‘cc’,’333’);
Insert into user(name,password) values(‘dd’,’444’);

采用PreparedStatement.addBatch()实现批处理

优点：发送的是预编译后的SQL语句，执行效率高。

缺点：只能应用在SQL语句相同，但参数不同的批处理中。因此此种形式的批处理经常用于在同一个表中批量插入数据，或批量更新表的数据。

4、获取插入新纪录的主键
statement.getGeneratedKeys();

package com.xiaozhi.clob.and.blob;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;

import com.xiaozhi.uitls.JdbcUtil;

/*
获取插入的记录的主键：INSERT时才有效。要求数据库能自动生成主键
use testdatabase;
create table autokeytable(
id int primary key auto_increment,
name varchar(20)
);
*/
public class GenAutoKeyTest {

public static void main(String[] args) {
ResultSet resultSet = null;
Connection connection = null;
PreparedStatement statement = null;
try{
connection = JdbcUtil.getConnection();
String sql = "insert into autokeytable (name) values(?)";
statement = connection.prepareStatement(sql,Statement.RETURN_GENERATED_KEYS);//默认行为
statement.setString(1, "admin");
statement.executeUpdate();
//获得插入的新纪录的主键
resultSet = statement.getGeneratedKeys();
if(resultSet.next())
System.out.println(resultSet.getObject(1));
}catch(Exception e){
e.printStackTrace();
}finally{
JdbcUtil.release(connection, statement, resultSet);
}
}

}

5、事务

Connection.setAutoCommit(false);  //start transaction

Connection.rollback();  // rollback

Connection.commit();   //commit

package com.xiaozhi.clob.and.blob;

/*
*  use testdatabase;
create table account(
id int primary key auto_increment,
name varchar(40),
money float
)character set utf8 collate utf8_general_ci;

insert into account(name,money) values('aaa',1000);
insert into account(name,money) values('bbb',1000);
insert into account(name,money) values('ccc',1000);

*/
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Savepoint;

import com.xiaozhi.uitls.JdbcUtil;

public class AccountDemo1 {
public static void main(String[] args) {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
try{
connection = JdbcUtil.getConnection();
//开启事务
connection.setAutoCommit(false);

String sql1 = "update account set money=money+100 where name='aaa'";
statement = connection.prepareStatement(sql1);
statement.executeUpdate();

int i = 1/0;

String sql2 = "update account set money=money-100 where name='bbb'";
statement = connection.prepareStatement(sql2);
statement.executeUpdate();

//关闭事务
connection.commit();

}catch(Exception e){
try {
//回滚
connection.rollback();
//关闭事务
connection.commit();
} catch (SQLException e1) {
e1.printStackTrace();
}
e.printStackTrace();
}finally{
JdbcUtil.release(connection, statement, resultSet);
}
}

}

设置回滚点

package com.xiaozhi.clob.and.blob;

/*
*  use testdatabase;
create table account(
id int primary key auto_increment,
name varchar(40),
money float
)character set utf8 collate utf8_general_ci;

insert into account(name,money) values('aaa',1000);
insert into account(name,money) values('bbb',1000);
insert into account(name,money) values('ccc',1000);

*/
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Savepoint;

import com.xiaozhi.uitls.JdbcUtil;

public class AccountDemo1 {
public static void main(String[] args) {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
Savepoint sp = null;
try{
connection = JdbcUtil.getConnection();
//开启事务
connection.setAutoCommit(false);

//设置回滚点
sp = connection.setSavepoint();

String sql1 = "update account set money=money+100 where name='aaa'";
statement = connection.prepareStatement(sql1);
statement.executeUpdate();

int i = 1/0;

String sql2 = "update account set money=money-100 where name='bbb'";
statement = connection.prepareStatement(sql2);
statement.executeUpdate();

//关闭事务
connection.commit();

}catch(Exception e){
try {
//回滚到回滚点
connection.rollback(sp);
//关闭事务
connection.commit();
} catch (SQLException e1) {
e1.printStackTrace();
}
e.printStackTrace();
}finally{
JdbcUtil.release(connection, statement, resultSet);
}
}

}

<
abb3
strong>6、事务的隔离级别[/b]

1）事务特性



2）出现的问题：

脏读：回滚之前看到的

重复读：事务未提交之前，有人给你打钱，你第一次查询是这个钱，第二次查询是另一个钱。

幻读:银行统计用户数，在这个过程中，有一个人注册为用户。



3）数据库共定义了四种隔离级别：

Serializable：可避免脏读、不可重复读、虚读情况的发生。（串行化）

Repeatable read：可避免脏读、不可重复读情况的发生。（可重复读）

Read committed：可避免脏读情况发生（读已提交）。

Read uncommitted：最低级别，以上情况均无法保证。(读未提交)

set   transaction isolation level 设置事务隔离级别

select @@tx_isolation 查询当前事务隔离级别




4)JDBC设置隔离级别:

//设置隔离级别
conn.setTransactionIsolation(Connection.TRANSACTION_REPEATABLE_READ);