/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.metamodel.xml;
import java.io.File;
import java.io.InputStream;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.apache.metamodel.MetaModelException;
import org.apache.metamodel.QueryPostprocessDataContext;
import org.apache.metamodel.data.DataSet;
import org.apache.metamodel.data.RowPublisher;
import org.apache.metamodel.data.RowPublisherDataSet;
import org.apache.metamodel.query.SelectItem;
import org.apache.metamodel.schema.Column;
import org.apache.metamodel.schema.ColumnType;
import org.apache.metamodel.schema.ImmutableSchema;
import org.apache.metamodel.schema.MutableColumn;
import org.apache.metamodel.schema.MutableSchema;
import org.apache.metamodel.schema.MutableTable;
import org.apache.metamodel.schema.Schema;
import org.apache.metamodel.schema.Table;
import org.apache.metamodel.util.Action;
import org.apache.metamodel.util.FileResource;
import org.apache.metamodel.util.Ref;
import org.apache.metamodel.util.Resource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;
/**
* XML datacontext which uses SAX parsing for fast and memory effecient reading
* of XML files.
*
* The DataContext requires the user to specify a set of (simplified) XPaths to
* define which elements are row delimitors and which elements or attributes are
* value/column definitions.
*/
public class XmlSaxDataContext extends QueryPostprocessDataContext {
private static final Logger logger = LoggerFactory.getLogger(XmlSaxDataContext.class);
public static final String COLUMN_NAME_ROW_ID = "row_id";
private final Ref<InputSource> _inputSourceRef;
private final Map<XmlSaxTableDef, Map<String, String>> _valueXpaths;
private String _schemaName;
private XmlSaxTableDef[] _tableDefs;
/**
* Constructs an XML DataContext based on SAX parsing.
*
* @param inputSourceRef
* a factory reference for the input source to read the XML from.
* The ref will be repeatedly called for each access to the file!
* @param tableDefs
* an array of table definitions, which provide instructions as
* to the xpaths to apply to the document.
*
* @see XmlSaxTableDef
*/
public XmlSaxDataContext(Ref<InputSource> inputSourceRef, XmlSaxTableDef... tableDefs) {
_inputSourceRef = inputSourceRef;
_tableDefs = tableDefs;
_valueXpaths = new HashMap<XmlSaxTableDef, Map<String, String>>();
_schemaName = null;
for (XmlSaxTableDef tableDef : tableDefs) {
LinkedHashMap<String, String> xpathMap = new LinkedHashMap<String, String>();
_valueXpaths.put(tableDef, xpathMap);
String[] valueXpaths = tableDef.getValueXpaths();
for (String valueXpath : valueXpaths) {
xpathMap.put(getName(tableDef, valueXpath), valueXpath);
}
}
}
public XmlSaxDataContext(final Resource resource, XmlSaxTableDef... tableDefs) {
this(createInputSourceRef(resource), tableDefs);
}
public XmlSaxDataContext(final File file, XmlSaxTableDef... tableDefs) {
this(createInputSourceRef(new FileResource(file)), tableDefs);
}
private static Ref<InputSource> createInputSourceRef(final Resource resource) {
return new Ref<InputSource>() {
@Override
public InputSource get() {
final InputStream in = resource.read();
return new InputSource(in);
}
};
}
@Override
protected Schema getMainSchema() throws MetaModelException {
final MutableSchema schema = new MutableSchema(getMainSchemaName());
for (XmlSaxTableDef tableDef : _tableDefs) {
final String rowXpath = tableDef.getRowXpath();
final MutableTable table = new MutableTable(getTableName(tableDef)).setSchema(schema).setRemarks(
"XPath: " + rowXpath);
final MutableColumn rowIndexColumn = new MutableColumn(COLUMN_NAME_ROW_ID, ColumnType.INTEGER)
.setColumnNumber(0).setNullable(false).setTable(table).setRemarks("Row/tag index (0-based)");
table.addColumn(rowIndexColumn);
for (String valueXpath : tableDef.getValueXpaths()) {
final MutableColumn column = new MutableColumn(getName(tableDef, valueXpath)).setRemarks("XPath: "
+ valueXpath);
if (valueXpath.startsWith("index(") && valueXpath.endsWith(")")) {
column.setType(ColumnType.INTEGER);
} else {
column.setType(ColumnType.STRING);
}
column.setTable(table);
table.addColumn(column);
}
schema.addTable(table);
}
return new ImmutableSchema(schema);
}
private XmlSaxTableDef getTableDef(Table table) {
for (XmlSaxTableDef tableDef : _tableDefs) {
if (getTableName(tableDef).equals(table.getName())) {
return tableDef;
}
}
throw new IllegalArgumentException("No table def found for table " + table);
}
private String getTableName(XmlSaxTableDef tableDef) {
String xpath = tableDef.getRowXpath();
int lastIndexOf = xpath.lastIndexOf('/');
if (lastIndexOf != -1) {
xpath = xpath.substring(lastIndexOf);
}
return xpath;
}
private String getName(XmlSaxTableDef tableDef, String xpath) {
String rowXpath = tableDef.getRowXpath();
if (xpath.startsWith(rowXpath)) {
xpath = xpath.substring(rowXpath.length());
}
return xpath;
}
@Override
protected String getMainSchemaName() throws MetaModelException {
if (_schemaName == null) {
// when querying the schema name for the first time, pick the first
// element of the document.
try {
SAXParserFactory saxFactory = SAXParserFactory.newInstance();
SAXParser saxParser = saxFactory.newSAXParser();
XMLReader xmlReader = saxParser.getXMLReader();
xmlReader.setContentHandler(new DefaultHandler() {
@Override
public void startElement(String uri, String localName, String qName, Attributes attributes)
throws SAXException {
if (qName != null && qName.length() > 0) {
_schemaName = '/' + qName;
throw new XmlStopParsingException();
}
}
});
xmlReader.parse(_inputSourceRef.get());
} catch (XmlStopParsingException e) {
logger.debug("Parsing stop signal thrown");
} catch (Exception e) {
logger.error("Unexpected error occurred while retrieving schema name", e);
if (e instanceof RuntimeException) {
throw (RuntimeException) e;
}
throw new IllegalStateException(e);
}
}
return _schemaName;
}
@Override
protected DataSet materializeMainSchemaTable(Table table, Column[] columns, int maxRows) {
final XmlSaxTableDef tableDef = getTableDef(table);
final String[] valueXpaths = new String[columns.length];
final SelectItem[] selectItems = new SelectItem[columns.length];
for (int i = 0; i < columns.length; i++) {
final Column column = columns[i];
selectItems[i] = new SelectItem(column);
valueXpaths[i] = getXpath(tableDef, column);
}
final Action<RowPublisher> rowPublisherAction = new Action<RowPublisher>() {
@Override
public void run(RowPublisher rowPublisher) throws Exception {
SAXParserFactory saxFactory = SAXParserFactory.newInstance();
SAXParser saxParser = saxFactory.newSAXParser();
XMLReader xmlReader = saxParser.getXMLReader();
xmlReader
.setContentHandler(new XmlSaxContentHandler(tableDef.getRowXpath(), rowPublisher, valueXpaths));
try {
xmlReader.parse(_inputSourceRef.get());
} catch (XmlStopParsingException e) {
logger.debug("Parsing stop signal thrown");
} catch (Exception e) {
logger.warn("Unexpected error occurred while parsing", e);
throw e;
} finally {
rowPublisher.finished();
}
}
};
return new RowPublisherDataSet(selectItems, maxRows, rowPublisherAction);
}
private String getXpath(XmlSaxTableDef tableDef, Column column) {
String columnName = column.getName();
if (COLUMN_NAME_ROW_ID.equals(columnName)) {
return "index(" + tableDef.getRowXpath() + ")";
}
String result = _valueXpaths.get(tableDef).get(columnName);
if (result == null) {
return columnName;
}
return result;
}
}