android - SchemaFactory 不支持平台级别 8 中的 W3C XML Schema？

Question

使用 Android SDK，纯空 Activity 中的以下代码会失败:

@Override
protected void onStart() {
    super.onStart();

    SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
}

2.2 模拟器 logcat 显示此异常:

06-28 05:38:06.107: WARN/dalvikvm(495): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
06-28 05:38:06.128: ERROR/AndroidRuntime(495): FATAL EXCEPTION: main
        java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example/com.example.HelloWorldActivity}: java.lang.IllegalArgumentException: http://www.w3.org/2001/XMLSchema
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
        at android.app.ActivityThread.access$2300(ActivityThread.java:125)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:123)
        at android.app.ActivityThread.main(ActivityThread.java:4627)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:521)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
        at dalvik.system.NativeStart.main(Native Method)
        Caused by: java.lang.IllegalArgumentException: http://www.w3.org/2001/XMLSchema
        at javax.xml.validation.SchemaFactory.newInstance(SchemaFactory.java:194)
        at com.example.HelloWorldActivity.onStart(HelloWorldActivity.java:26)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1129)
        at android.app.Activity.performStart(Activity.java:3781)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2636)
        ... 11 more

Javadoc of SchemaFactory提到“平台默认 SchemaFactory 以特定于实现的方式定位。W3C XML Schema 必须有一个平台默认 SchemaFactory。”

Answer 1

在得到适合我的答案之前，我遇到了同样的问题并阅读了很多帖子。对常量的引用在 Dalvik 上不起作用。我发现我必须修改我的代码才能使用 Xerces-for-Android 项目，然后我才能获得我所追求的 xml 验证。这很可能是您通过变量引用所做的事情。以下是设置的详细信息和一些示例代码，展示了如何让验证在 android 上运行。

以下内容对我有用:

1. 创建验证实用程序。
2. 将 xml 和 xsd 都放入 android 操作系统上的文件中，并针对它使用验证实用程序。
3. 使用 Xerces-For-Android 进行验证。

Android 确实支持一些我们可以使用的包，我创建了我的 xml 验证实用程序，基于:http://docs.oracle.com/javase/1.5.0/docs/api/javax/xml/validation/package-summary.html

我最初的沙盒测试使用 java 非常顺利，然后我尝试将其移植到 Dalvik 并发现我的代码不起作用。 Dalvik 不支持某些东西，所以我做了一些修改。

我找到了对 android 的 xerces 的引用，所以我修改了我的沙盒测试(以下不适用于 android，之后的示例可以):

import java.io.File;

import javax.xml.XMLConstants;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Source;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;

import org.w3c.dom.Document;

/**
 * A Utility to help with xml communication validation.
 */
public class XmlUtil {

    /**
     * Validation method. 
     * Base code/example from: http://docs.oracle.com/javase/1.5.0/docs/api/javax/xml/validation/package-summary.html
     * 
     * @param xmlFilePath The xml file we are trying to validate.
     * @param xmlSchemaFilePath The schema file we are using for the validation. This method assumes the schema file is valid.
     * @return True if valid, false if not valid or bad parse. 
     */
    public static boolean validate(String xmlFilePath, String xmlSchemaFilePath) {

        // parse an XML document into a DOM tree
        DocumentBuilder parser = null;
        Document document;

        // Try the validation, we assume that if there are any issues with the validation
        // process that the input is invalid.
        try {
            // validate the DOM tree
            parser = DocumentBuilderFactory.newInstance().newDocumentBuilder();
            document = parser.parse(new File(xmlFilePath));

            // create a SchemaFactory capable of understanding WXS schemas
            SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);

            // load a WXS schema, represented by a Schema instance
            Source schemaFile = new StreamSource(new File(xmlSchemaFilePath));
            Schema schema = factory.newSchema(schemaFile);

            // create a Validator instance, which can be used to validate an instance document
            Validator validator = schema.newValidator();
            validator.validate(new DOMSource(document));
        } catch (Exception e) {
            // Catches: SAXException, ParserConfigurationException, and IOException.
            return false;
        }     

        return true;
    }
}

上述代码必须进行一些修改才能与 xerces for android ( http://gc.codehum.com/p/xerces-for-android/ ) 一起使用。获取项目需要SVN，以下是一些crib note:

download xerces-for-android
    download silk svn (for windows users) from http://www.sliksvn.com/en/download
        install silk svn (I did complete install)
        Once the install is complete, you should have svn in your system path.
        Test by typing "svn" from the command line.
        I went to my desktop then downloaded the xerces project by:
            svn checkout http://xerces-for-android.googlecode.com/svn/trunk/ xerces-for-android-read-only
        You should then have a new folder on your desktop called xerces-for-android-read-only

使用上面的jar(最终我会把它做成一个jar，直接复制到我的源代码中进行快速测试。如果你想这样做，你可以用Ant快速制作jar(http://ant.apache.org/manual/using.html) )，我能够获得以下内容来进行我的 xml 验证:

import java.io.File;
import java.io.IOException;

import mf.javax.xml.transform.Source;
import mf.javax.xml.transform.stream.StreamSource;
import mf.javax.xml.validation.Schema;
import mf.javax.xml.validation.SchemaFactory;
import mf.javax.xml.validation.Validator;
import mf.org.apache.xerces.jaxp.validation.XMLSchemaFactory;

import org.xml.sax.SAXException;

/**
 * A Utility to help with xml communication validation.
 */public class XmlUtil {

    /**
     * Validation method. 
     * 
     * @param xmlFilePath The xml file we are trying to validate.
     * @param xmlSchemaFilePath The schema file we are using for the validation. This method assumes the schema file is valid.
     * @return True if valid, false if not valid or bad parse or exception/error during parse. 
     */
    public static boolean validate(String xmlFilePath, String xmlSchemaFilePath) {

        // Try the validation, we assume that if there are any issues with the validation
        // process that the input is invalid.
        try {
            SchemaFactory  factory = new XMLSchemaFactory();
            Source schemaFile = new StreamSource(new File(xmlSchemaFilePath));
            Source xmlSource = new StreamSource(new File(xmlFilePath));
            Schema schema = factory.newSchema(schemaFile);
            Validator validator = schema.newValidator();
            validator.validate(xmlSource);
        } catch (SAXException e) {
            return false;
        } catch (IOException e) {
            return false;
        } catch (Exception e) {
            // Catches everything beyond: SAXException, and IOException.
            e.printStackTrace();
            return false;
        } catch (Error e) {
            // Needed this for debugging when I was having issues with my 1st set of code.
            e.printStackTrace();
            return false;
        }

        return true;
    }
}

一些旁注:

为了创建文件，我制作了一个简单的文件实用程序来将字符串写入文件:

public static void createFileFromString(String fileText, String fileName) {
    try {
        File file = new File(fileName);
        BufferedWriter output = new BufferedWriter(new FileWriter(file));
        output.write(fileText);
        output.close();
    } catch ( IOException e ) {
       e.printStackTrace();
    }
}

我还需要写一个我可以访问的区域，所以我使用了:

String path = this.getActivity().getPackageManager().getPackageInfo(getPackageName(), 0).applicationInfo.dataDir;   

有点hackish，它有效。我确信有一种更简洁的方法可以做到这一点，但是我想我会分享我的成功，因为我没有找到任何好的例子。