描述

Blob接口用于操作BLOB类型数据。

java.sql.Blob接口的核心目标是安全、高效地操作数据库中的大二进制数据，方法主要分为数据读取、数据写入、数据更新、资源管理四类。

详细接口说明请参考JDBC官方网站 (opens new window)。

方法

YashanDB JDBC驱动对BLOB接口有如下方法：

方法	返回类型	备注
length()	long	-
getBytes(long pos, int length)	byte[]	-
setBytes(long pos, byte[] bytes)	int	-
setBytes(long pos, byte[] bytes, 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。
setBinaryStream(long pos)	java.io.OutputStream	-
getBinaryStream()	java.io.InputStream	-
getBinaryStream(long pos, long length)	java.io.InputStream	-
free()	void	-
void truncate(long len)	void	不适用于存算一体分布式集群部署。

示例

package quickstart;

import java.io.InputStream;
import java.io.OutputStream;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;

public class BlobExample {

    public static Connection getConnection()
            throws SQLException, ClassNotFoundException {
        String url = "jdbc:yasdb://192.168.1.2:1688/yasdb";
        Properties info = new Properties();
        info.setProperty("user", "username");
        info.setProperty("password", "passwd");
        Class.forName("com.yashandb.jdbc.Driver");
        return DriverManager.getConnection(url, info);
    }

    public static void main(String[] args) throws Exception {
        BlobExample example = new BlobExample();
        try (Connection conn = getConnection()) {
            example.demoLength(conn);
            example.demoGetBytes(conn);
            example.demoSetBytes(conn);
            example.demoSetBytesWithOffset(conn);
            example.demoSetBinaryStream(conn);
            example.demoGetBinaryStream(conn);
            example.demoGetBinaryStreamPartial(conn);
            example.demoFree(conn);
            example.demoTruncate(conn);
        }
    }

    // 1. length() 方法示例
    public void demoLength(Connection conn) throws SQLException {
        Blob blob = conn.createBlob();
        blob.setBytes(1, "Hello".getBytes());
        long length = blob.length();
        System.out.println("BLOB length: " + length);
    }

    // 2. getBytes() 方法示例
    public void demoGetBytes(Connection conn) throws SQLException {
        Blob blob = conn.createBlob();
        blob.setBytes(1, "Hello World".getBytes());
        byte[] part = blob.getBytes(7, 5); // Gets "World"
        System.out.println("Retrieved partial data: " + new String(part));
    }

    // 3. setBytes() 方法示例
    public void demoSetBytes(Connection conn) throws SQLException {
        Blob blob = conn.createBlob();
        blob.setBytes(1, "Hello".getBytes());
        blob.setBytes(6, " World".getBytes()); // Append
        System.out.println("Complete data: " + new String(blob.getBytes(1, 11)));
    }

    // 4. setBytes() 带偏移量示例
    public void demoSetBytesWithOffset(Connection conn) throws SQLException {
        Blob blob = conn.createBlob();
        byte[] data = "ABCDEFGHIJ".getBytes();
        blob.setBytes(1, data, 2, 5); // Start from offset 2, take 5 bytes
        System.out.println("Result: " + new String(blob.getBytes(1, 5))); // Outputs "CDEFG"
    }

    // 5. setBinaryStream() 方法示例
    public void demoSetBinaryStream(Connection conn) throws Exception {
        Blob blob = conn.createBlob();
        try (OutputStream os = blob.setBinaryStream(1)) {
            os.write("Stream Data".getBytes());
        }
        System.out.println("Stream writing completed, length: " + blob.length());
    }
    // 6. getBinaryStream() 方法示例
    public void demoGetBinaryStream(Connection conn) throws Exception {
        Blob blob = conn.createBlob();
        blob.setBytes(1, "Stream Example".getBytes());
        try (InputStream is = blob.getBinaryStream()) {
            byte[] buffer = new byte[1024];
            int bytesRead = is.read(buffer);
            System.out.println("Stream reading: " + new String(buffer, 0, bytesRead));
        }
    }

    // 7. getBinaryStream() 带位置和长度示例 (YashanDB扩展方法)
    // 注意: 这是YashanDB JDBC驱动的扩展方法，非JDBC标准
    public void demoGetBinaryStreamPartial(Connection conn) throws Exception {
        Blob blob = conn.createBlob();
        blob.setBytes(1, "Partial Stream Access".getBytes());
        // 使用YashanDB扩展方法: getBinaryStream(long pos, long length)
        try (InputStream is = blob.getBinaryStream(9, 6)) {
            byte[] data = is.readAllBytes();
            System.out.println("Partial reading: " + new String(data)); // Outputs "Stream"
        }
    }

    // 8. free() 方法示例
    public void demoFree(Connection conn) throws SQLException {
        Blob blob = conn.createBlob();
        blob.setBytes(1, "Test".getBytes());
        System.out.println("Length before freeing: " + blob.length());
        blob.free(); // Release resources
    }

    // 9. truncate() 方法示例
    public void demoTruncate(Connection conn) throws SQLException {
        Blob blob = conn.createBlob();
        blob.setBytes(1, "Very Long String".getBytes());
        blob.truncate(4); // Truncate to 4 bytes
        System.out.println("After truncation: " + new String(blob.getBytes(1, 4))); // Outputs "Very"
    }

}

正常情况下，程序输出如下：

BLOB length: 5
Retrieved partial data: World
Complete data: Hello World
Result: CDEFG
Stream writing completed, length: 11
Stream reading: Stream Example
Partial reading: Stream
Length before freeing: 4
After truncation: Very