JDBC（五）——处理大数据对象CLOB和BLOB

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大数据对象主要有CLOB（character large object）和BLOB（binary large object）两种类型的字段。在CLOB中可以存储大字符数据对象，比如长篇小说；在BLOB中可存储二进制大数据对象，比如图片、电影、音乐。

处理CLOB

如何将一个txt文本插入到数据库中，数据库新建属性content，类型longtext，java中txt文本对应于File类型。

获取指定内容的文件流

File context = book.getContext();

获取文件流的输入流

InputStream inputStream = new FileInputStream(context);

为输入流设置指定参数

pstat.setAsciiStream(1, InputStream, context.length());

要输出某一个大文本的内容

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ResultSet rs = pstat.executeQuery();
Clob c = rs.getClob(“context”); // Retrieves the value of the designated column in the current row of this ResultSet object as a Clob object
String context = c.getSubString(1, (int)c.length()); // Retrieves a copy of the specified substring in the CLOB value designated by this Clob object
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package com.java.jdbc.chap06.sec01;

import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.util.ArrayList;
import java.util.List;

import com.java.jdbc.model.Book;
import com.java.jdbc.util.DbUtil;

public class Demo1 {
	private static DbUtil dbUtil = new DbUtil();
	private static int addBook(Book book) throws Exception{
		Connection con = dbUtil.getCon();
		String sql = "INSERT INTO t_book VALUES (?, ?, ?, ?, ?, ?);";
		PreparedStatement pstat = con.prepareStatement(sql);
		pstat.setInt(1, book.getId());
		pstat.setString(2, book.getBookName());
		pstat.setString(3, book.getAuthor());
		pstat.setFloat(4, book.getPrice());
		pstat.setString(5, book.getBookTypeId());
		File context = book.getContext(); //获取文件
		InputStream inputStream = new FileInputStream(context); //获取文件输入流
		pstat.setAsciiStream(6, inputStream, context.length());
		int rst = pstat.executeUpdate();
		dbUtil.close(pstat, con);
		return rst;
	}
	public static void main(String[] args) throws Exception {
		File context = new File("F:\\eclipsework\\JDBCPro\\src\\com\\java\\jdbc\\chap06\\Longtext insert.txt"); //或者F:/eclipsework/JDBCPro/src/com/java/jdbc/chap06/Longtext insert.txt
		Book book = new Book(8, "物理", "longtext", 90, "4", context);
		int rst = addBook(book);
		if (rst == 1){
			System.out.println("添加成功！");
		} else {
			System.out.println("添加失败！");
		}
	}
}

while循环语句，可以执行多次，只要条件为真，就执行循环语句，直到条件为假；
if是条件语句，单词执行，满足条件表达式则执行语句。
输出id=?行的数据：

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import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.sql.Clob;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import com.java.jdbc.model.Book;
import com.java.jdbc.util.DbUtil;

public class Demo1 {
	private static DbUtil dbUtil = new DbUtil();
	/**
	 * 添加数据，包含CLOB（大文本）文件
	 * @param book
	 * @return
	 * @throws Exception
	 */
	private static int addBook(Book book) throws Exception{
		Connection con = dbUtil.getCon();
		String sql = "INSERT INTO t_book VALUES (?, ?, ?, ?, ?, ?)";
		PreparedStatement pstat = con.prepareStatement(sql);
		pstat.setInt(1, book.getId());
		pstat.setString(2, book.getBookName());
		pstat.setString(3, book.getAuthor());
		pstat.setFloat(4, book.getPrice());
		pstat.setString(5, book.getBookTypeId());
		File context = book.getContext(); //获取文件
		InputStream inputStream = new FileInputStream(context); //获取文件输入流
		pstat.setAsciiStream(6, inputStream, context.length());
		int rst = pstat.executeUpdate();
		dbUtil.close(pstat, con);
		return rst;
	}
	/**
	 * 读取id=?行的数据
	 * @param id
	 * @throws Exception
	 */
	public static void getBook(int id) throws Exception {
		Connection con = dbUtil.getCon();
		String sql = "SELECT * FROM t_book WHERE id = ?";
		PreparedStatement pstat = con.prepareStatement(sql);
		pstat.setInt(1, id);
		ResultSet rs = pstat.executeQuery();
		if (rs.next()) { //由于是输出id=?的单行，所以只输出一次
			String bookName  = rs.getString("bookName");
			String author = rs.getString("author");
			float price = rs.getFloat("price");
			String bookTypeId = rs.getString("bookTypeId");
			//输出大文本
			Clob c = rs.getClob("context");
			String context = c.getSubString(1, (int) c.length());
			System.out.println("图书编号：" + id + ",名称：" + bookName 
					+ ",作者：" + author + ",价格：" + price + ",类型：" 
					+ bookTypeId + ",内容" + context);
		}
		dbUtil.close(pstat, con);
	}
	public static void main(String[] args) throws Exception {
	/*	File context = new File("F:\\eclipsework\\JDBCPro\\src\\com\\java\\jdbc\\chap06\\Longtext insert.txt");
		Book book = new Book(8, "物理", "longtext", 90, "4", context);
		int rst = addBook(book);
		if (rst == 1){
			System.out.println("添加成功！");
		} else {
			System.out.println("添加失败！");
		}*/
		getBook(8);
	}
}

处理BLOB

获取指定内容的文件流

File pic = book.getPic();

获取图片文件流的输入流

InputStream inputStream2 = new FileInputStream(pic);

为输入流设置指定参数

pstat.setBinaryStream(1, InputStream2, pic.length()); //二进制的

要输出某一个打文本的内容

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ResultSet rs = pstat.executeQuery();
Blob b = rs.getBlob(“pic”);
//图片没法显示到eclipse，一般把它存到另一个地方去，如F盘
FileOutputStream fos = new FileOutputStream(new File(“f:/pic2.jpg”)); //定义一个输出流
out.write(b.getBytes(1, (int)b.length())); //直接写
out.close();