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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 {undefinedprivate static Connection conn;static {undefinedtry {undefinedClass.forName("oracle.jdbc.driver.OracleDriver");conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl","scott","tiger");} catch (ClassNotFoundException e) {undefinede.printStackTrace();} catch (SQLException e) {undefinede.printStackTrace();}}public static void main(String[] args) throws SQLException, IOException {undefinedtestInsert();testUpdate();testRead();}private static void testInsert() throws SQLException {undefinedString sql = "insert into test_clob values(1, empty_clob())";Statement stm = conn.createStatement();stm.execute(sql);}private static void testUpdate() throws SQLException, IOException {undefinedString sql = "select content from test_clob where id = 1 for update";Statement stm = conn.createStatement();ResultSet rs = stm.executeQuery(sql);while (rs.next()) {undefinedClob c = rs.getClob(1);c.truncate(0);// clearWriter w = c.setCharacterStream(1);//The first position is 1w.write("abc");w.close();c.setString(c.length() + 1, "abc");conn.commit();}}private static void testRead() throws SQLException, IOException {undefinedString sql = "select content from test_clob where id = 1";PreparedStatement pstm = conn.prepareStatement(sql);ResultSet rs = pstm.executeQuery();while (rs.next()) {undefinedClob 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) {undefinedSystem.out.println(s);}r.close();}}}
