java clob是什么，让我们一起了解一下？
CLOB是内置类型，将字符大对象存储为数据库表某一行中的一个列值。默认情况下，驱动程序使用SQL locator实现Clob对象，这意味着CLOB对象包含一个指向SQL CLOB数据的逻辑指针而不是数据本身。
在JAVA如何使用CLOB进行操作？
在绝大多数情况下，有2种方法使用CLOB。
1、相对比较小的，可以用String进行直接操作，把CLOB看成字符串类型即可。
2、如果比较大，可以用 getAsciiStream 或者 getUnicodeStream 以及对应的 setAsciiStream 和 setUnicodeStream 即可。
（1）读取数据：
ResultSet rs = stmt.executeQuery("SELECT TOP 1 * FROM Test1");
rs.next();
Reader reader = rs.getCharacterStream(2);（2）插入数据：
PreparedStatement pstmt = con.prepareStatement("INSERT INTO test1 (c1_id, c2_vcmax) VALUES (?, ?)");
pstmt.setInt(1, 1);
pstmt.setString(2, htmlStr);
pstmt.executeUpdate();（3）更新数据：
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM test1");
rs.next();
Clob clob = rs.getClob(2);
long pos = clob.position("dog", 1);
clob.setString(1, "cat", len, 3);
rs.updateClob(2, clob);
rs.updateRow();那么java是如何操作数据库clob字段的？
示例代码如下：
package com.test.db.clob;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.Writer;
import java.sql.Clob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class ClobTest {undefined
private static Connection conn;
static {undefined
try {undefined
Class.forName("oracle.jdbc.driver.OracleDriver");
conn = DriverManager.getConnection(
"jdbc:oracle:thin:@localhost:1521:orcl","scott","tiger");
} catch (ClassNotFoundException e) {undefined
e.printStackTrace();
} catch (SQLException e) {undefined
e.printStackTrace();
}
}
public static void main(String[] args) throws SQLException, IOException {undefined
testInsert();
testUpdate();
testRead();
}
private static void testInsert() throws SQLException {undefined
String sql = "insert into test_clob values(1, empty_clob())";
Statement stm = conn.createStatement();
stm.execute(sql);
}
private static void testUpdate() throws SQLException, IOException {undefined
String sql = "select content from test_clob where id = 1 for update";
Statement stm = conn.createStatement();
ResultSet rs = stm.executeQuery(sql);
while (rs.next()) {undefined
Clob c = rs.getClob(1);
c.truncate(0);// clear
Writer w = c.setCharacterStream(1);//The first position is 1
w.write("abc");
w.close();
c.setString(c.length() + 1, "abc");
conn.commit();
}
}
private static void testRead() throws SQLException, IOException {undefined
String sql = "select content from test_clob where id = 1";
PreparedStatement pstm = conn.prepareStatement(sql);
ResultSet rs = pstm.executeQuery();
while (rs.next()) {undefined
Clob clob = rs.getClob("content");
System.out.println("clob.getSubString(1, 2) --> " + clob.getSubString(1, 2));
System.out.println("clob.getSubString(1, (int)clob.length()) --> " +
clob.getSubString(1, (int)clob.length()));
BufferedReader r = new BufferedReader(clob.getCharacterStream());
String s;
while ((s = r.readLine()) != null) {undefined
System.out.println(s);
}
r.close();
}
}
}以上就是小编今天的分享了，希望可以帮助到大家。