描述

NClob接口用于操作NCLOB类型数据。

java.sql.NClob是JDBC规范中用于操作数据库国家字符集大字符对象的接口。NClob继承java.sql.Clob，自身没有新增方法，因此方法名称、参数类型和返回类型与Clob相同。

详细接口定义请参考JDBC官方网站 (opens new window)。

方法

YashanDB JDBC驱动对NCLOB接口有如下方法（单机部署/共享集群/分布式集群部署）：

方法	返回类型
length()	long
getSubString(long pos, int length)	String
setString(long pos, String str)	int
setString(long pos, String str, int offset, int len)	int
setAsciiStream(long pos)	java.io.OutputStream
setCharacterStream(long pos)	java.io.Writer
getCharacterStream()	java.io.Reader
getCharacterStream(long pos, long length)	Reader
getAsciiStream()	java.io.InputStream
free()	void
truncate(long len)	void

YashanDB JDBC驱动对NCLOB接口有如下方法（存算一体分布式集群部署）：

方法	返回类型	备注
length()	long	-
getSubString(long pos, int length)	String	-
setString(long pos, String str)	int	-
setString(long pos, String str, int offset, int len)	int	存算一体分布式集群部署中只能调用本接口将数据写入至CN节点的临时LOB中，无法将数据写至DN节点上。
getCharacterStream()	java.io.Reader	-
getAsciiStream()	java.io.InputStream	-
setAsciiStream(long pos)	java.io.OutputStream	-
setCharacterStream(long pos)	java.io.Writer	-
getCharacterStream(long pos, long length)	Reader	-
truncate(long len)	void	存算一体分布式集群部署中只能调用本接口将数据写入至CN节点的临时LOB中，无法将数据写至DN节点上。
free()	void	-

说明：

• YashanDB JDBC 1.10.3不支持position(String searchstr, long start)和position(Clob searchstr, long start)方法，调用时抛出SQLFeatureNotSupportedException。

示例

以下示例使用createNClob()创建NCLOB对象，通过setCharacterStream()写入Unicode文本，使用setNClob()保存到数据库，并通过getNClob()读取内容。

package quickstart;

import java.io.Reader;
import java.io.Writer;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.NClob;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Properties;

public class NClobInterfaceExample {
    private static final String URL =
            "jdbc:yasdb://192.168.1.2:1688/yasdb";
    private static final String TABLE = "jdbc_nclob_example";

    public static void main(String[] args) throws Exception {
        Properties properties = new Properties();
        properties.setProperty("user", "username");
        properties.setProperty("password", "passwd");
        Class.forName("com.yashandb.jdbc.Driver");

        try (Connection connection =
                     DriverManager.getConnection(URL, properties)) {
            try (Statement statement = connection.createStatement()) {
                statement.execute("DROP TABLE IF EXISTS " + TABLE);
                statement.execute(
                        "CREATE TABLE " + TABLE
                                + " (id INTEGER PRIMARY KEY, content NCLOB)");
            }

            NClob nclob = connection.createNClob();
            try (Writer writer = nclob.setCharacterStream(1)) {
                writer.write("YashanDB JDBC NCLOB示例");
            }

            try (PreparedStatement statement = connection.prepareStatement(
                    "INSERT INTO " + TABLE + " VALUES (?, ?)")) {
                statement.setInt(1, 1);
                statement.setNClob(2, nclob);
                statement.executeUpdate();
            }
            nclob.free();

            try (Statement statement = connection.createStatement();
                 ResultSet resultSet = statement.executeQuery(
                         "SELECT content FROM " + TABLE + " WHERE id = 1")) {
                if (resultSet.next()) {
                    NClob storedNClob = resultSet.getNClob(1);
                    try (Reader reader =
                                 storedNClob.getCharacterStream()) {
                        StringBuilder content = new StringBuilder();
                        char[] buffer = new char[1024];
                        int count;
                        while ((count = reader.read(buffer)) != -1) {
                            content.append(buffer, 0, count);
                        }
                        System.out.println("NCLOB content: " + content);
                    }
                    storedNClob.free();
                }
            }
        } finally {
            try (Connection connection =
                         DriverManager.getConnection(URL, properties);
                 Statement statement = connection.createStatement()) {
                statement.execute("DROP TABLE IF EXISTS " + TABLE);
            }
        }
    }
}

正常情况下，程序输出如下：

NCLOB content: YashanDB JDBC NCLOB示例