在实际开发中，程序需要把大文本或二进制数据保存到数据库。
基本概念：大数据也称之为LOB（Large Objects），LOB又分为clob（大文本，text）
和blob（二进制数据，图像、声音、二进制文等）
对MySQL而言只有blob，而没有clob，MySQL存储大文本采用的是Text，Text和blob分别又分为：
TINYTEXT、TEXT、MEDIUMTEXT和LONGTEXT
TINYBLOB、BLOB、MEDIUMBLOB和BLOB
对于MySQL中的Text类型，可调用如下方法设置：
PreparedStatement.setCharacterStream(index，reader，length)；
//注意length长度须设置，并且为int型
对于MySQL中的Text类型，可调用如下方法设置：
reader = resultSet.getCharacterStream(i);
reader = resultSet.getClob(i).getCharacterStream();
String s = resultSet.getString(i);
先把数据库连接代码写好
db.properties
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/testclob
username=root
password=root
JdbcUtils
package cn.itcast.utils;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Properties;
public class JdbcUtils {
private static Properties prop = new Properties();
static {
try {
prop.load(JdbcUtils.class.getClassLoader().getResourceAsStream("db.properties"));
Class.forName(prop.getProperty("driver"));
} catch (Exception e) {
throw new ExceptionInInitializerError(e);
}
}
public static Connection getConnection() throws Exception {
return DriverManager.getConnection(prop.getProperty("url"), prop.getProperty("username"), prop.getProperty("password"));
}
public static void release(Connection conn, Statement st, ResultSet rs) {
if (rs != null) {
try {
rs.close(); //throw new
} catch (Exception e) {
e.printStackTrace();
}
rs = null;
}
if (st != null) {
try {
st.close();
} catch (Exception e) {
e.printStackTrace();
}
st = null;
}
if (conn != null) {
try {
conn.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
然后在src下面新建一个1.txt文件
mysql中建表：
create table testClob(
id varchar(40) primary key,
resume text
);
写入数据：
@Test
public void insert() {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
String sql = "insert into testclob(id,resume) values(?,?)";
ps = conn.prepareStatement(sql);
ps.setString(1, "1");
//第二个问号是一个大文本
//注意，现在是java工程，web工程不这样写，如果非要这么写，1.txt文件应该在bin目录下
File file = new File("src/1.txt");
FileReader reader = new FileReader(file);
int length = (int) file.length();
ps.setCharacterStream(2, reader, length);//reader流与文件1.txt相关联
int num = ps.executeUpdate();
if (num > 0) {
System.out.println("插入成功 ");
}
} catch (Exception e) {
e.printStackTrace();
} finally {
JdbcUtils.release(conn, ps, rs);
}
}
读出数据：将数据读出来重新写到D盘
@Test
public void read() {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
String sql = "select id,resume from testclob where id='1'";
ps = conn.prepareStatement(sql);
rs = ps.executeQuery();
if (rs.next()) {
//读数据
Reader reader = rs.getCharacterStream("resume");//作为流返回
//写数据到D盘下
FileWriter writer = new FileWriter("D:\\copy.txt");
//从流里读数据
try {
int len = 0;
char buffer[] = new char[1024];
while ((len = reader.read(buffer)) > 0) {
writer.write(buffer, 0, len);
}
} finally {
if (reader != null) {
reader.close();
}
if (writer != null) {
writer.close();
}
}
}
} catch (Exception e) {
e.printStackTrace();
} finally {
JdbcUtils.release(conn, ps, rs);
}
}
对于MySQL中的BLOB类型，可调用如下方法设置：
PreparedStatement.setBinaryStream(i，inputStream，length)；
//注意length长度须设置，并且为int型
对于MySQL中的BLOB类型，可调用如下方法设置：
InputStream in = resultSet.getBinaryStream(i);
InputStream in = resultSet.getBlob(i).getBinaryStream();
mysql中建表：
create table testblob(
id varchar(40) primary key,
image blob
);
读写数据
@Test
public void insert() {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
String sql = "insert into testblob(id,image) values(?,?)";
ps = conn.prepareStatement(sql);
ps.setString(1, "1");
//注意，现在是java工程，web工程不这样写，如果非要这么写，1.txt文件应该在bin目录下
File file = new File("src/1.jpg");
FileInputStream in = new FileInputStream(file);
int length = (int) file.length();
ps.setBinaryStream(2, in, length);
ps.executeUpdate();
} catch (Exception e) {
e.printStackTrace();
} finally {
JdbcUtils.release(conn, ps, rs);
}
}
@Test
public void read() {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
String sql = "select id,image from testblob where id='1'";
ps = conn.prepareStatement(sql);
rs = ps.executeQuery();
if (rs.next()) {
InputStream in = rs.getBinaryStream("image");
OutputStream out = new FileOutputStream("D:\\1.jpg");
try {
int len = 0;
byte[] buffer = new byte[1024];
while ((len = in.read(buffer)) > 0) {
out.write(buffer, 0, len);
}
} finally {
if (in != null) {
in.close();
}
if (out != null) {
out.close();
}
}
}
} catch (Exception e) {
e.printStackTrace();
} finally {
JdbcUtils.release(conn, ps, rs);
}
}
一般情况下，不会把大数据直接存到数据库里，而是存在硬盘上。