java - JAXP 撒克逊-he : XMLfile StreamSource doesn't release file access after parsing error

Question

我正在使用 JAXP 规范 API 与 Saxon-HE API 相结合，主要目的是开发一个应用程序，该应用程序使用可配置的 XSLT 样式表转换 XML 文件，能够覆盖生成的输出文档。我跳过详细信息，因为我创建了一个示例项目来说明遇到的问题:

用例:如果出现转换错误，将 xml 文件移动到另一个目录(可能是错误目录)会引发访问异常。

当我基于 File 实例(指向 XML 文件)实例化 StreamSource 时，如果发生某些解析错误，移动文件会引发“该进程无法访问该文件，因为它正在被另一个进程使用。”异常(exception)。

这是我为说明问题而编写的一个主要单类应用程序:

package com.sample.xslt.application;

import net.sf.saxon.Configuration;
import net.sf.saxon.lib.FeatureKeys;

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardCopyOption;

import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMResult;
import javax.xml.transform.stream.StreamSource;

public class XsltApplicationSample {

  public static void main(String[] args) throws Exception {

    if (args.length != 2) {
      throw new RuntimeException("Two arguments are expected : <xslFilePath> <inputFilePath>");
    }
    String xslFilePath = args[0];
    String xmlFilePath = args[1];

    TransformerFactory factory = TransformerFactory.newInstance();
    factory.setAttribute(FeatureKeys.ALLOW_MULTITHREADING, Boolean.TRUE);
    factory.setAttribute(FeatureKeys.RECOVERY_POLICY,
        new Integer(Configuration.RECOVER_WITH_WARNINGS));

    Source xslSource = new StreamSource(new File(xslFilePath));
    Source xmlSource = new StreamSource(new File(xmlFilePath));
    Transformer transformer = factory.newTransformer(xslSource);

    try {
      transformer.transform(xmlSource, new DOMResult());

    } catch (TransformerException e) {
      System.out.println(e.getMessage());
    }

    // move input file to tmp directory (for example, could be configured error dir)

    File srcFile = Paths.get(xmlFilePath).toFile();
    File tempDir = new File(System.getProperty("java.io.tmpdir"));

    Path destFilePath = new File(tempDir, srcFile.getName()).toPath();

    try {
      Files.move(srcFile.toPath(), destFilePath, StandardCopyOption.REPLACE_EXISTING);
    } catch (SecurityException | IOException e) {
      System.out.println(e.getMessage());
    }
  }
}

配置的 xslt 转换文件内容必须有效才能重现。如果输入的xml文件为空，则会产生转换/解析错误，但不会发生访问文件错误。

要重现的输入文件示例:

<root>
    <elem>
</root>

标准输出示例:

JAXP: find factoryId =javax.xml.transform.TransformerFactory
JAXP: find factoryId =javax.xml.parsers.SAXParserFactory
JAXP: loaded from fallback value: com.sun.org.apache.xerces.internal.jaxp.SAXParserFactoryImpl
JAXP: created new instance of class com.sun.org.apache.xerces.internal.jaxp.SAXParserFactoryImpl using ClassLoader: null
JAXP: find factoryId =javax.xml.parsers.SAXParserFactory
JAXP: loaded from fallback value: com.sun.org.apache.xerces.internal.jaxp.SAXParserFactoryImpl
JAXP: created new instance of class com.sun.org.apache.xerces.internal.jaxp.SAXParserFactoryImpl using ClassLoader: null
JAXP: find factoryId =javax.xml.parsers.DocumentBuilderFactory
JAXP: loaded from fallback value: com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl
JAXP: created new instance of class com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl using ClassLoader: null
JAXP: find factoryId =javax.xml.parsers.SAXParserFactory
JAXP: loaded from fallback value: com.sun.org.apache.xerces.internal.jaxp.SAXParserFactoryImpl
JAXP: created new instance of class com.sun.org.apache.xerces.internal.jaxp.SAXParserFactoryImpl using ClassLoader: null
Error on line 3 column 3 of input_err.xml:
  SXXP0003: Error reported by XML parser: The element type "elem" must be terminated by the
  matching end-tag "</elem>".
org.xml.sax.SAXParseException; systemId: file:/C:/<path>/input_err.xml; lineNumber: 3; columnNumber: 3; The element type "elem" must be terminated by the matching end-tag "</elem>".
C:\<path>\input_err.xml -> C:\<path>\AppData\Local\Temp\input_err.xml: The process cannot access the file because it is being used by another process.

使用命令行(我使用 Eclipse):

java ... -Djaxp.debug=1 -Dfile.encoding=UTF-8 -classpath <...> com.sample.xslt.application.XsltApplicationSample C:\<path>\transform.xsl C:\<path>\input_err.xml

使用的pom.xml:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.sample</groupId>
    <artifactId>XsltExampleProject</artifactId>
    <version>1.0.0-SNAPSHOT</version>

    <name>XsltExampleProject</name>
    <description>XSLT example project</description>

    <dependencies>
        <dependency>
            <groupId>net.sf.saxon</groupId>
            <artifactId>Saxon-HE</artifactId>
            <version>9.7.0-7</version>
        </dependency>

        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.5</version>
        </dependency>

        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.2.1</version>
        </dependency>
    </dependencies>

    <build>
        <sourceDirectory>src</sourceDirectory>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.3</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

我使用的解决方法是将 xml 输入文件的内容作为字符串加载到内存中，请参阅以下内容:

String xmlContent = FileUtils.readFileToString(new File(xmlFilePath), StandardCharsets.UTF_8);

Source xslSource = new StreamSource(new File(xslFilePath));
Source xmlSource = new StreamSource(new StringReader(xmlContent));

初始化 Transformer 时我错过了什么吗？默认解析的 SAX 解析器应该重写为 Saxon 推荐的另一个 API？我认为Xerces解析器是根据调试日志记录使用的，但是它与Saxon提供的变压器实现完全兼容吗？我对这个有点困惑..

感谢您的帮助!

Answer 1

从问题后面的评论线程来看，这似乎是 JDK 提供的 XML 解析器中的错误/缺陷。您的选择是:

(a) 报告错误并耐心等待修复

(b) 使用 Apache Xerces 解析器

(c) 不提供 File，而是提供 FileInputStream，然后自行关闭它。

我的建议是 (b)，因为 Apache Xerces 解析器比 JDK 中的版本可靠得多。