java - blob.getBinaryStream 独立关闭

Question

我有一个从 oracle 数据库中获取 blob 的 java 方法(我使用的是 ojdbc8.jar)。此方法将 blob 写入 OutputStream(对于客户端):

// OutputStream os = response.getOutputStream();  // earlier
// Blob blob = resultSet.getBlob("data_binary");  // earlier

    int length;
    int bufSize = 4096;
    byte buffer[] = new byte[bufSize];
    try (InputStream is = blob.getBinaryStream()) {
        while ((length = is.read(buffer, 0, bufSize)) != -1) {
            out.write(buffer, 0, length);
            out.flush();
        }
        out.flush();
    }

并返回 InputStream(用于缓存):

return blob.getBinaryStream();

当我尝试(在另一个类上)将此 InputStream 写入磁盘时:

    try (OutputStream os = new FileOutputStream(fileOnTheDisk)) {
        IOUtils.copy(blobIS, os);
    } catch (IOException e) {
        e.printStackTrace();
    }

我遇到异常:

java.io.IOException: Closed Connection
at oracle.jdbc.driver.OracleBlobInputStream.needBytes(OracleBlobInputStream.java:204)
at oracle.jdbc.driver.OracleBufferedStream.readInternal(OracleBufferedStream.java:169)
at oracle.jdbc.driver.OracleBufferedStream.read(OracleBufferedStream.java:143)
at oracle.jdbc.driver.OracleBufferedStream.read(OracleBufferedStream.java:132)
at org.apache.commons.io.IOUtils.copyLarge(IOUtils.java:1025)
at org.apache.commons.io.IOUtils.copy(IOUtils.java:999)
at ru.miit.databasereader.OracleDatabaseReader.getbo(OracleDatabaseReader.java:262)
at ru.miit.contentservlet.ContentGetter.getObject(ContentGetter.java:85)
at ru.miit.contentservlet.ContentServlet.doGet(ContentServlet.java:131)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:651)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:409)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:754)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1376)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
Caused by: java.sql.SQLRecoverableException: Closed Connection
at oracle.sql.BLOB.getDBAccess(BLOB.java:1122)
at oracle.sql.BLOB.getBytes(BLOB.java:348)
at oracle.jdbc.driver.OracleBlobInputStream.needBytes(OracleBlobInputStream.java:181)
... 31 more

我需要一个解决方案，如何将此 blob.getBinaryStream() 写入另一个类的磁盘并了解问题所在。

我试图用这种(获取)方法将这个 blob 流写入磁盘，但没有得到异常。只有当我将这个流返回到另一个类(class)时，我才会有异常(exception)。

已更新

完整代码。磁盘缓存:

public class DiskCache {

public void put(final String location, final String name, final InputStream blobIS, OutpuStream servletOS) {

    DatabaseReader databaseReader = new DatabaseReader ();

    BinaryObject binaryobject = databaseReader.getBinaryDataByImageId(imageId, servletOS);

    File fileOnTheDisk = new File(location + name);

    try (OutputStream os = new FileOutputStream(fileOnTheDisk)) {
        IOUtils.copy(binaryobject.getIS(), os);
    } catch (IOException e) {
        e.printStackTrace();
    }

}

数据库读取器:

public class DatabaseReader{

public Connection getConnection() throws NamingException, SQLException {

    Context initialContext = null;
    try {
        initialContext = new InitialContext();
        DataSource dataSource = (DataSource) initialContext.lookup(DATASOURCE_NAME);
        OracleConnection connection = (OracleConnection) dataSource.getConnection().unwrap(OracleConnection.class);
        return connection;
    } finally {
        if (initialContext != null){
            initialContext.close();
        }
    }

}
    public BinaryObject getBinaryDataByImageId(final String imageId, OutputStream osServlet) throws SQLException, NamingException, IOException{

     String sqlQuery = "***";

     BinaryObject binaryObject = null;
     try (Connection connection = getConnection();
            OraclePreparedStatement preparedStatement = (OraclePreparedStatement) connection
                    .prepareStatement(sqlQuery)) {
        try (ResultSet resultSet = preparedStatement.executeQuery()) {

            resultSet.next();
            Blob blob = resultSet.getBlob("blob_data");
            writeToStream(blob, osServlet); 
            binaryObject = new BinaryObject(imageId, blob.getBinaryStream());

        }
      }
      return binaryObject;
    }


    public void writeToStream(Blob blobData, OutputStream out) throws IOException, SQLException {

    int length;
    int bufSize = 4096;
    byte buffer[] = new byte[bufSize];
    try (InputStream is = blobData.getBinaryStream()) {
        while ((length = is.read(buffer, 0, bufSize)) != -1) {
            out.write(buffer, 0, length);
            out.flush();
        }
        out.flush();

    }

}
}

JNDI:

    <Resource name="jdbc/database" auth="Container"
    type="javax.sql.DataSource" maxActive="100" 
    maxIdle="30" maxWait="1000"
    username="***" 
    password="***"
    driverClassName="oracle.jdbc.OracleDriver"
    url="jdbc:oracle:thin***"/>

Answer 1

在每个 ResultSet.next 步骤中，一个 blob 应该只被读取一次。在结果集关闭(它应该关闭)之后，以及在读取 blob 的输入流之后(也关闭流)，你就不走运了。

如果您想快速为客户端提供服务，并在缓存中存储副本，您需要同时执行这两项操作:

// OutputStream os = response.getOutputStream();  // earlier
// Blob blob = resultSet.getBlob("data_binary");  // earlier
// OutputStream cacheOut
final int bufSize = 4096;
byte[] buffer = new byte[bufSize];
int length;
try (InputStream is = blob.getBinaryStream()) {
    while ((length = is.read(buffer, 0, bufSize)) != -1) {
        out.write(buffer, 0, length);
        out.flush();
        cacheOut.write(buffer, 0, length);
    }
    out.flush();
    cacheOut.close();
}

任何其他任务都是内存密集型任务。