执行基本 XQuery 操作
您可以使用 XQueryExecutable 实例(使用 XFactory.prepareXQuery 方法创建的实例),对 XQuery 表达式进行求值。
关于此任务
可以使用 JAXP StreamSource 对象或使用纯 Java™ 字符串对象,将 XQuery 表达式传递到 XFactory.prepareXQuery 方法。生成的 XQueryExecutable 实例对于线程是安全的,且可复用以针对多个 XML 输入文档对 XQuery 表达式进行求值。
过程
示例
以下是准备和执行已解释 XQuery 表达式的基本示例。
// Create a string for the XQuery expression
String expression = "/doc/name[@first='David']";
// Create the factory
XFactory factory = XFactory.newInstance();
// Create the XQueryExecutable
XQueryExecutable xQueryExecutable = factory.prepareXQuery(expression);
// Create the input XML source
String xml = "<doc<name first='John'>Wrong</name><name first='David'>Correct</name></doc>";
// Execute the expression and store the results in an XSequenceCursor
XSequenceCursor xSequenceCursor = xQueryExecutable.execute(new StreamSource(new ByteArrayInputStream(xml.getBytes())));
以下为准备和执行已编译 XQuery 表达式的基本示例。
// Create a string for the XQuery expression
String expression = "/doc/name[@first='David']";
// Create the factory
XFactory factory = XFactory.newInstance();
// Create a new static context from the factory
XStaticContext xStaticContext = factory.newStaticContext();
// Set the mode to compile for the processor
xStaticContext.setUseCompiler(true);
// Create the XQueryExecutable
XQueryExecutable xQueryExecutable = factory.prepareXQuery(expression, xStaticContext);
// Create the input XML source
String xml = "<doc><name first='John'>Wrong</name><name first='David'>Correct</name></doc>";
// Execute the expression and store the results in an XSequenceCursor
XSequenceCursor xSequenceCursor = xQueryExecutable.execute(new StreamSource(new ByteArrayInputStream(xml.getBytes())));
以下是使用模式感知准备和执行已解释 XQuery 表达式的基本示例。
// Create a string for the XQuery expression
String expression = "/my:doc/name[@first='David']/@first";
// Create the factory
XFactory factory = XFactory.newInstance();
// Create the schema source
String schema = "<xsd:schema xmlns:xsd='http://www.w3.org/2001/XMLSchema'" +
" targetNamespace='http://www.schematype.ibm.com/UDSimple'" +
" xmlns:my='http://www.schematype.ibm.com/UDSimple'" +
" xmlns:smokey='http://www.schematype.ibm.com/UDSimple'>"
+" <xsd:element name='doc'>"
+ "<xsd:complexType> "
+ "<xsd:sequence>"
+ "<xsd:element name='name' minOccurs='0' maxOccurs='unbounded'>"
+ "<xsd:complexType>"
+ "<xsd:attribute name='first' type='xsd:string' use='optional'/>"
+ "</xsd:complexType>"
+ "</xsd:element>"
+ "</xsd:sequence>"
+ "</xsd:complexType>"
+ "</xsd:element>"
+ "</xsd:schema>";
// Load the schema
factory.registerSchema(new StreamSource(new ByteArrayInputStream(schema.getBytes())));
// Turn on validation
factory.setValidating(true);
// Create a new static context from the factory
XStaticContext xStaticContext = factory.newStaticContext();
// Add a new namespace
xStaticContext.declareNamespace("my", "http://www.schematype.ibm.com/UDSimple");
// Create the XQueryExecutable
XQueryExecutable xQueryExecutable = factory.prepareXQuery(expression, xStaticContext);
// Create the input XML source
String xml = "<my:doc xmlns:my='http://www.schematype.ibm.com/UDSimple'>" +
"<name first='John'/><name first='David'/></my:doc>";
// Execute the expression and store the results in an XSequenceCursor
XSequenceCursor xSequenceCursor = xQueryExecutable.execute(new StreamSource(new ByteArrayInputStream(xml.getBytes())));