直接上代碼：

package com.it.test;

import java.io.BufferedReader;
import java.io.StringWriter;
import java.io.UnsupportedEncodingException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import oracle.sql.BLOB;

 
public class Test {

    /***
     * 讀取oracleCLOB字段內容
     * 
     * @param conn
     * @return
     */
    public static String readCLOB(Connection conn) {
        String sql = "select 大字段1,大字段2 from 印章基本信息_char_ccbb where yzbm=‘2‘";
        String content = "";
        try {
            conn.setAutoCommit(
 
false);
            PreparedStatement ps1 = conn.prepareStatement(sql);
            ResultSet rs1 = ps1.executeQuery();
            while (rs1.next()) {
                oracle.sql.CLOB clob = (oracle.sql.CLOB) rs1.getClob("大字段1");

                BufferedReader in = new BufferedReader(clob.getCharacterStream());
                StringWriter out 
 
= new StringWriter();
                int c;
                while ((c = in.read()) != -1) {
                    out.write(c);
                }
                content = out.toString();
                System.out.println(content);// 輸出CLOB內容
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return content;
    }

    /***
     * 讀取oracle的blob轉換為字符串
     * 
     * @param conn
     * @return
     */
    public static String ConvertBLOBtoString(Connection conn) {
        String newStr = ""; // 返回字符串
        long BlobLength; // BLOB字段長度
        byte[] bytes; // BLOB臨時存儲字節數組
        int i = 1; // 循環變量
        Statement st = null;
        try {
            st = conn.createStatement();
            ResultSet rs = st.executeQuery("select 大字段2 from 印章基本信息_char_ccbb where yzbm=‘2‘");
            while (rs.next()) {
                BLOB blob = (BLOB) rs.getBlob("大字段2");
                byte[] msgContent = blob.getBytes(); // BLOB轉換為字節數組
                BlobLength = blob.length(); // 獲取BLOB長度
                if (msgContent == null || BlobLength == 0) // 如果為空，返回空值
                {
                    return "";
                } else {
                    while (i < BlobLength) // 循環處理字符串轉換，每次1024；Oracle字符串限制最大4k
                    {
                        bytes = blob.getBytes(i, 1024);
                        i = i + 1024;
                        newStr = newStr + new String(bytes, "gb2312");
                    }
                }
            }
            System.out.println(newStr);
            System.out.println(newStr.length());

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            if (st != null) {
                try {
                    st.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return newStr;
    }
}

以上內容參考自：https://blog.csdn.net/u010965170/article/details/78729794

java讀取blob，clob轉換為字符串