I have an XPath expression that searches for a static value. In this example, "test" is that value:
XPathExpression expr = xpath.compile("//doc[contains(., 'test')]/*/text()");
How can I pass a variable instead of a fixed string? I use Java with Eclipse. Is there a way to use the value of a Java String to declare an XPath variable?
You can define a variable resolver and have the evaluation of the expression resolve variables such as $myvar, for example:
XPathExpression expr = xpath.compile("//doc[contains(., $myVar)]/*/text()");
There's a fairly good explanation here. I haven't actually done this before myself, so I might have a go and provide a more complete example.
Update:
Given this a go, works a treat. For an example of a very simple implementation, you could define a class that returns the value for a given variable from a map, like this:
class MapVariableResolver implements XPathVariableResolver {
// local store of variable name -> variable value mappings
Map<String, String> variableMappings = new HashMap<String, String>();
// a way of setting new variable mappings
public void setVariable(String key, String value) {
variableMappings.put(key, value);
}
// override this method in XPathVariableResolver to
// be used during evaluation of the XPath expression
#Override
public Object resolveVariable(QName varName) {
// if using namespaces, there's more to do here
String key = varName.getLocalPart();
return variableMappings.get(key);
}
}
Now, declare and initialise an instance of this resolver in the program, for example
MapVariableResolver vr = new MapVariableResolver() ;
vr.setVariable("myVar", "text");
...
XPath xpath = factory.newXPath();
xpath.setXPathVariableResolver(vr);
Then, during evaluation of the XPath expression XPathExpression expr = xpath.compile("//doc[contains(., $myVar)]/*/text()");, the variable $myVar will be replaced with the string text.
Nice question, I learnt something useful myself!
You don't need to evaluate Java (or whatever else PL variables in XPath). In C# (don't know Java well) I'll use:
string XPathExpression =
"//doc[contains(., " + myVar.ToString() + ")]/*/text()";
XmlNodelist result = xmlDoc.SelectNodes(XPathExpression);
Apart from this answer here, that explains well how to do it with the standard Java API, you could also use a third-party library like jOOX that can handle variables in a simple way:
List<String> list = $(doc).xpath("//doc[contains(., $1)]/*", "test").texts();
I use something similar to #brabster:
// expression: "/message/PINConfiguration/pinValue[../keyReference=$keyReference]";
Optional<Node> getNode(String xpathExpression, Map<String, String> variablesMap)
throws XPathExpressionException {
XPath xpath = XPathFactory.newInstance().newXPath();
xpath.setXPathVariableResolver(qname -> variablesMap.get(qname.getLocalPart()));
return Optional.ofNullable((Node) xpath.evaluate(xpathExpression, document,
XPathConstants.NODE));
}
Optional<Node> getNode(String xpathExpression) throws XPathExpressionException {
return getNode(xpathExpression, Collections.emptyMap());
}
Related
<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom" xmlns:georss="http://www.georss.org/georss"><title>USGS All Earthquakes, Past Week</title><updated>2020-02-26T21:28:38Z</updated><author><name>U.S. Geological Survey</name><uri>https://earthquake.usgs.gov/</uri></author><id>https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_week.atom</id><link rel="self" href="https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_week.atom"/><icon>https://earthquake.usgs.gov/favicon.ico</icon>
<entry><id>urn:earthquake-usgs-gov:ci:39084495</id><title>M 0.6 - 13km WNW of Anza, CA</title><updated>2020-02-26T21:23:25.292Z</updated><link rel="alternate" type="text/html" href="https://earthquake.usgs.gov/earthquakes/eventpage/ci39084495"/><summary type="html"><![CDATA[<dl><dt>Time</dt><dd>2020-02-26 21:19:49 UTC</dd><dd>2020-02-26 13:19:49 -08:00 at epicenter</dd><dt>Location</dt><dd>33.602°N 116.804°W</dd><dt>Depth</dt><dd>4.62 km (2.87 mi)</dd></dl>]]></summary><georss:point>33.6016667 -116.8035</georss:point><georss:elev>-4620</georss:elev><category label="Age" term="Past Hour"/><category label="Magnitude" term="Magnitude 0"/><category label="Contributor" term="ci"/><category label="Author" term="ci"/></entry></feed>
I'm Trying to extract information from this xml, I did manage to do it but im not sure how its working, more precisely i don't understand why the value seems to be so deep in the nodes. the code im using is as follows
builder = fac.newDocumentBuilder();
Document doc = builder.parse(source);
NodeList nodeList = doc.getDocumentElement().getChildNodes();
for(int i=0;i < nodeList.getLength();i++){
Node node = nodeList.item(i);
if (node.getNodeName().equals("entry")){
Element element = (Element) node;
String nl1 = element.getElementsByTagName("georss:point").item(0).getChildNodes().item(0).getNodeValue();
}
}
I had expected that after getting the element by the tag i should be able to get the value right away but instead i have to go two levels deeper, can anyone explain why?
EDIT: typo
You are asking, why it seems to be so deeply nested. I will answer that first and then suggest three other approaches you also could consider to work with that xml in java.
Why is it so nested
Element.getElementsByTagName() returns a NodeList which contains 0-n elements. You know that you only have one but the xml-engine not. So you need to say: Give me the first element of that list (.item(0)).
Now you have the element point but you want to have its content. You are accessing the content as a child, but again: there could be multiple children (like other tags), so again you need to tell which element.
Alternative approaches
Access the content as text content: element.getElementsByTagName("georss:point").item(0).getTextContent();
Using Xpath:
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();
XPathExpression expr = xpath.compile("//*[local-name()='point']");
String evaluate = expr.evaluate(doc);
System.out.println(evaluate);
Kindly note that the xpath //*[local-name()='point'] is not the best way. You should work with the namespaces which would require some more code.
Use xml to bean mapping, for example with JAXB
You should really consider this approach as it basically allows you to have Pojo objects with all content of the xml (like the age, magnitude, ...) and simply have the xml transformed in a object like this:
public class Entry{
private String id;
private String title;
...
private String point;
private String age;
private String magnitude;
...
I hope this helps.
I have a XML file resulted from an input java file. I also have xPath expressions for the XML file.
I need a function that receives one xPath expression and return its java element (in the abstract syntax tree). I tried the below code:
First extract XML element based on the input xPath expression.
XPath xPath = XPathFactory.newInstance().newXPath();
String query = "//unit[1]/unit[1]/class[1]/block[1]/function[6]"; //a method
Node node = (Node) xPath.compile(query).evaluate(XmlDocument, XPathConstants.NODE);
However, I do not know how to link extracted XML node to Java element in the source code.
PS:
The reslut should be a node in the abstract syntax tree. I have AST created by spoon. Therefore, in the above example, I want to extract related CtMethodImpl.
node.getTextContent() is not the answer as it is possible that there is more than one instance with the similar text content.
To the best of my knowledge there is no 'direct' way of doing this.
This: "//unit[1]/unit[1]/class[1]/block[1]/function[6]" is what we call a signature in the sense that it uniquely identifies an element (somehow).
What I would do is to create a spoon processor and go through the entire AST checking each element to see if it matches the signature.
public class ProcessorExample <E extends CtElement> extends AbstractProcessor<E> {
HashMap<String, Node> nodes;
//Sets your XML Nodes here, sorted by signature
public void setNodes(HashMap<String, Node> nodes) {
this.nodes = nodes;
}
#Override
public void process(E element) {
if (nodes.containsKey(signature(element))) {
Node n = nodes.get(signature(element));
//YOU FOUND IT!
}
}
private String signature(E element) {
//YOU MUST PROVIDE THIS IMPLEMENTATION
//TO MATCH YOUR "//unit[1]/unit[1]/class[1]/block[1]/function[6]"
//KIND OF SIGNATURE
return null;
}
}
When my XML looks like this (no xmlns) then I can easly query it with XPath like /workbook/sheets/sheet[1]
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<workbook>
<sheets>
<sheet name="Sheet1" sheetId="1" r:id="rId1"/>
</sheets>
</workbook>
But when it looks like this then I can't
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<workbook xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships">
<sheets>
<sheet name="Sheet1" sheetId="1" r:id="rId1"/>
</sheets>
</workbook>
Any ideas?
In the second example XML file the elements are bound to a namespace. Your XPath is attempting to address elements that are bound to the default "no namespace" namespace, so they don't match.
The preferred method is to register the namespace with a namespace-prefix. It makes your XPath much easier to develop, read, and maintain.
However, it is not mandatory that you register the namespace and use the namespace-prefix in your XPath.
You can formulate an XPath expression that uses a generic match for an element and a predicate filter that restricts the match for the desired local-name() and the namespace-uri(). For example:
/*[local-name()='workbook'
and namespace-uri()='http://schemas.openxmlformats.org/spreadsheetml/2006/main']
/*[local-name()='sheets'
and namespace-uri()='http://schemas.openxmlformats.org/spreadsheetml/2006/main']
/*[local-name()='sheet'
and namespace-uri()='http://schemas.openxmlformats.org/spreadsheetml/2006/main'][1]
As you can see, it produces an extremely long and verbose XPath statement that is very difficult to read (and maintain).
You could also just match on the local-name() of the element and ignore the namespace. For example:
/*[local-name()='workbook']/*[local-name()='sheets']/*[local-name()='sheet'][1]
However, you run the risk of matching the wrong elements. If your XML has mixed vocabularies (which may not be an issue for this instance) that use the same local-name(), your XPath could match on the wrong elements and select the wrong content:
Your problem is the default namespace. Check out this article for how to deal with namespaces in your XPath: http://www.edankert.com/defaultnamespaces.html
One of the conclusions they draw is:
So, to be able to use XPath
expressions on XML content defined in
a (default) namespace, we need to
specify a namespace prefix mapping
Note that this doesn't mean that you have to change your source document in any way (though you're free to put the namespace prefixes in there if you so desire). Sounds strange, right? What you will do is create a namespace prefix mapping in your java code and use said prefix in your XPath expression. Here, we'll create a mapping from spreadsheet to your default namespace.
XPathFactory factory = XPathFactory.newInstance();
XPath xpath = factory.newXPath();
// there's no default implementation for NamespaceContext...seems kind of silly, no?
xpath.setNamespaceContext(new NamespaceContext() {
public String getNamespaceURI(String prefix) {
if (prefix == null) throw new NullPointerException("Null prefix");
else if ("spreadsheet".equals(prefix)) return "http://schemas.openxmlformats.org/spreadsheetml/2006/main";
else if ("xml".equals(prefix)) return XMLConstants.XML_NS_URI;
return XMLConstants.NULL_NS_URI;
}
// This method isn't necessary for XPath processing.
public String getPrefix(String uri) {
throw new UnsupportedOperationException();
}
// This method isn't necessary for XPath processing either.
public Iterator getPrefixes(String uri) {
throw new UnsupportedOperationException();
}
});
// note that all the elements in the expression are prefixed with our namespace mapping!
XPathExpression expr = xpath.compile("/spreadsheet:workbook/spreadsheet:sheets/spreadsheet:sheet[1]");
// assuming you've got your XML document in a variable named doc...
Node result = (Node) expr.evaluate(doc, XPathConstants.NODE);
And voila...Now you've got your element saved in the result variable.
Caveat: if you're parsing your XML as a DOM with the standard JAXP classes, be sure to call setNamespaceAware(true) on your DocumentBuilderFactory. Otherwise, this code won't work!
All namespaces that you intend to select from in the source XML must be associated with a prefix in the host language. In Java/JAXP this is done by specifying the URI for each namespace prefix using an instance of javax.xml.namespace.NamespaceContext. Unfortunately, there is no implementation of NamespaceContext provided in the SDK.
Fortunately, it's very easy to write your own:
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import javax.xml.namespace.NamespaceContext;
public class SimpleNamespaceContext implements NamespaceContext {
private final Map<String, String> PREF_MAP = new HashMap<String, String>();
public SimpleNamespaceContext(final Map<String, String> prefMap) {
PREF_MAP.putAll(prefMap);
}
public String getNamespaceURI(String prefix) {
return PREF_MAP.get(prefix);
}
public String getPrefix(String uri) {
throw new UnsupportedOperationException();
}
public Iterator getPrefixes(String uri) {
throw new UnsupportedOperationException();
}
}
Use it like this:
XPathFactory factory = XPathFactory.newInstance();
XPath xpath = factory.newXPath();
HashMap<String, String> prefMap = new HashMap<String, String>() {{
put("main", "http://schemas.openxmlformats.org/spreadsheetml/2006/main");
put("r", "http://schemas.openxmlformats.org/officeDocument/2006/relationships");
}};
SimpleNamespaceContext namespaces = new SimpleNamespaceContext(prefMap);
xpath.setNamespaceContext(namespaces);
XPathExpression expr = xpath
.compile("/main:workbook/main:sheets/main:sheet[1]");
Object result = expr.evaluate(doc, XPathConstants.NODESET);
Note that even though the first namespace does not specify a prefix in the source document (i.e. it is the default namespace) you must associate it with a prefix anyway. Your expression should then reference nodes in that namespace using the prefix you've chosen, like this:
/main:workbook/main:sheets/main:sheet[1]
The prefix names you choose to associate with each namespace are arbitrary; they do not need to match what appears in the source XML. This mapping is just a way to tell the XPath engine that a given prefix name in an expression correlates with a specific namespace in the source document.
If you are using Spring, it already contains org.springframework.util.xml.SimpleNamespaceContext.
import org.springframework.util.xml.SimpleNamespaceContext;
...
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();
SimpleNamespaceContext nsc = new SimpleNamespaceContext();
nsc.bindNamespaceUri("a", "http://some.namespace.com/nsContext");
xpath.setNamespaceContext(nsc);
XPathExpression xpathExpr = xpath.compile("//a:first/a:second");
String result = (String) xpathExpr.evaluate(object, XPathConstants.STRING);
I've written a simple NamespaceContext implementation (here), that takes a Map<String, String> as input, where the key is a prefix, and the value is a namespace.
It follows the NamespaceContext spesification, and you can see how it works in the unit tests.
Map<String, String> mappings = new HashMap<>();
mappings.put("foo", "http://foo");
mappings.put("foo2", "http://foo");
mappings.put("bar", "http://bar");
context = new SimpleNamespaceContext(mappings);
context.getNamespaceURI("foo"); // "http://foo"
context.getPrefix("http://foo"); // "foo" or "foo2"
context.getPrefixes("http://foo"); // ["foo", "foo2"]
Note that it has a dependency on Google Guava
Make sure that you are referencing the namespace in your XSLT
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"
xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships" >
Startlingly, if I don't set factory.setNamespaceAware(true); then the xpath you mentioned does work with and without namespaces at play. You just aren't able to select things "with namespace specified" only generic xpaths. Go figure. So this may be an option:
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(false);
Two things to add to the existing answers:
I don't know whether this was the case when you asked the question: With Java 10, your XPath actually works for the second document if you don't use setNamespaceAware(true) on the document builder factory (falseis the default).
If you do want to use setNamespaceAware(true), other answers have already shown how to do this using a namespace context. However, you don't need to provide the mapping of prefixes to namespaces yourself, as these answers do: It's already there in the document element, and you can use that for your namespace context:
import java.util.Iterator;
import javax.xml.namespace.NamespaceContext;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
public class DocumentNamespaceContext implements NamespaceContext {
Element documentElement;
public DocumentNamespaceContext (Document document) {
documentElement = document.getDocumentElement();
}
public String getNamespaceURI(String prefix) {
return documentElement.getAttribute(prefix.isEmpty() ? "xmlns" : "xmlns:" + prefix);
}
public String getPrefix(String namespaceURI) {
throw new UnsupportedOperationException();
}
public Iterator<String> getPrefixes(String namespaceURI) {
throw new UnsupportedOperationException();
}
}
The rest of the code is as in the other answers. Then the XPath /:workbook/:sheets/:sheet[1] yields the sheet element. (You could also use a non-empty prefix for the default namespace, as the other answers do, by replacing prefix.isEmpty() by e.g. prefix.equals("spreadsheet") and using the XPath /spreadsheet:workbook/spreadsheet:sheets/spreadsheet:sheet[1].)
P.S.: I just found here that there's actually a method Node.lookupNamespaceURI(String prefix), so you could use that instead of the attribute lookup:
public String getNamespaceURI(String prefix) {
return documentElement.lookupNamespaceURI(prefix.isEmpty() ? null : prefix);
}
Also, note that namespaces can be declared on elements other than the document element, and those wouldn't be recognized (by either version).
Is there any String replacement mechanism in Java, where I can pass objects with a text, and it replaces the string as it occurs?
For example, the text is:
Hello ${user.name},
Welcome to ${site.name}.
The objects I have are user and site. I want to replace the strings given inside ${} with its equivalent values from the objects. This is same as we replace objects in a velocity template.
Use StringSubstitutor from Apache Commons Text.
Dependency import
Import the Apache commons text dependency using maven as bellow:
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-text</artifactId>
<version>1.10.0</version>
</dependency>
Example
Map<String, String> valuesMap = new HashMap<String, String>();
valuesMap.put("animal", "quick brown fox");
valuesMap.put("target", "lazy dog");
String templateString = "The ${animal} jumped over the ${target}.";
StringSubstitutor sub = new StringSubstitutor(valuesMap);
String resolvedString = sub.replace(templateString);
Take a look at the java.text.MessageFormat class, MessageFormat takes a set of objects, formats them, then inserts the formatted strings into the pattern at the appropriate places.
Object[] params = new Object[]{"hello", "!"};
String msg = MessageFormat.format("{0} world {1}", params);
My preferred way is String.format() because its a oneliner and doesn't require third party libraries:
String message = String.format("Hello! My name is %s, I'm %s.", name, age);
I use this regularly, e.g. in exception messages like:
throw new Exception(String.format("Unable to login with email: %s", email));
Hint: You can put in as many variables as you like because format() uses Varargs
I threw together a small test implementation of this. The basic idea is to call format and pass in the format string, and a map of objects, and the names that they have locally.
The output of the following is:
My dog is named fido, and Jane Doe owns him.
public class StringFormatter {
private static final String fieldStart = "\\$\\{";
private static final String fieldEnd = "\\}";
private static final String regex = fieldStart + "([^}]+)" + fieldEnd;
private static final Pattern pattern = Pattern.compile(regex);
public static String format(String format, Map<String, Object> objects) {
Matcher m = pattern.matcher(format);
String result = format;
while (m.find()) {
String[] found = m.group(1).split("\\.");
Object o = objects.get(found[0]);
Field f = o.getClass().getField(found[1]);
String newVal = f.get(o).toString();
result = result.replaceFirst(regex, newVal);
}
return result;
}
static class Dog {
public String name;
public String owner;
public String gender;
}
public static void main(String[] args) {
Dog d = new Dog();
d.name = "fido";
d.owner = "Jane Doe";
d.gender = "him";
Map<String, Object> map = new HashMap<String, Object>();
map.put("d", d);
System.out.println(
StringFormatter.format(
"My dog is named ${d.name}, and ${d.owner} owns ${d.gender}.",
map));
}
}
Note: This doesn't compile due to unhandled exceptions. But it makes the code much easier to read.
Also, I don't like that you have to construct the map yourself in the code, but I don't know how to get the names of the local variables programatically. The best way to do it, is to remember to put the object in the map as soon as you create it.
The following example produces the results that you want from your example:
public static void main(String[] args) {
Map<String, Object> map = new HashMap<String, Object>();
Site site = new Site();
map.put("site", site);
site.name = "StackOverflow.com";
User user = new User();
map.put("user", user);
user.name = "jjnguy";
System.out.println(
format("Hello ${user.name},\n\tWelcome to ${site.name}. ", map));
}
I should also mention that I have no idea what Velocity is, so I hope this answer is relevant.
Here's an outline of how you could go about doing this. It should be relatively straightforward to implement it as actual code.
Create a map of all the objects that will be referenced in the template.
Use a regular expression to find variable references in the template and replace them with their values (see step 3). The Matcher class will come in handy for find-and-replace.
Split the variable name at the dot. user.name would become user and name. Look up user in your map to get the object and use reflection to obtain the value of name from the object. Assuming your objects have standard getters, you will look for a method getName and invoke it.
There are a couple of Expression Language implementations out there that does this for you, could be preferable to using your own implementation as or if your requirments grow, see for example JUEL and MVEL
I like and have successfully used MVEL in at least one project.
Also see the Stackflow post JSTL/JSP EL (Expression Language) in a non JSP (standalone) context
Handlebars.java might be a better option in terms of a Velocity-like syntax with other server-side templating features.
http://jknack.github.io/handlebars.java/
Handlebars handlebars = new Handlebars();
Template template = handlebars.compileInline("Hello {{this}}!");
System.out.println(template.apply("Handlebars.java"));
I use GroovyShell in java to parse template with Groovy GString:
Binding binding = new Binding();
GroovyShell gs = new GroovyShell(binding);
// this JSONObject can also be replaced by any Java Object
JSONObject obj = new JSONObject();
obj.put("key", "value");
binding.setProperty("obj", obj)
String str = "${obj.key}";
String exp = String.format("\"%s\".toString()", str);
String res = (String) gs.evaluate(exp);
// value
System.out.println(str);
I created this utility that uses vanilla Java. It combines two formats... {} and %s style from String.format.... into one method call. Please note it only replaces empty {} brackets, not {someWord}.
public class LogUtils {
public static String populate(String log, Object... objects) {
log = log.replaceAll("\\{\\}", "%s");
return String.format(log, objects);
}
public static void main(String[] args) {
System.out.println(populate("x = %s, y ={}", 5, 4));;
}
}
Since Java 15 you have the method String.formatted() (see documentation).
str.formatted(args) is the equivalent of String.format(str, args) with less ceremony.
For the example mentioned in the question, the method could be used as follows:
"Hello %s, Welcome to %s.".formatted(user.getName(), site.getName())
Good news. Java is most likely going to have string templates (probably from version 21).
See the string templates proposal (JEP 430) here.
It will be something along the lines of this:
String name = "John";
String info = STR."I am \{name}";
System.out.println(info); // I am John
P.S. Kotlin is 100% interoperable with Java. It supports cleaner string templates out of the box:
val name = "John"
val info = "I am $name"
println(info) // I am John
Combined with extension functions, you can achieve the same thing the Java template processors (e.g. STR) will do.
There is nothing out of the box that is comparable to velocity since velocity was written to solve exactly that problem. The closest thing you can try is looking into the Formatter
http://cupi2.uniandes.edu.co/site/images/recursos/javadoc/j2se/1.5.0/docs/api/java/util/Formatter.html
However the formatter as far as I know was created to provide C like formatting options in Java so it may not scratch exactly your itch but you are welcome to try :).
I have a class with an attribute and getter method:
public Class MyClass
{
private String myValue = "foo";
public String getMyValue();
}
I would like to be able to use the value of foo in a formatted string as such:
String someString = "Your value is {myValue}."
String result = Formatter.format(someString, new MyClass());
// result is now "Your value is foo."
That is, I would like to have some function like .format above which takes a format string specifying properties on some object, and an instance with those properties, and formats the string accordingly.
Is it possible to do accomplish this feat in Java?
you could use JUEL for this. it's an implementation of the Java Expression Language. the code is rather compact and looks like this:
ExpressionFactory factory = new ExpressionFactoryImpl();
// create a context and add a Person object to the context, this variable will be used
// in the property replacement
// objects of type Person have two fields: firstName and lastName
SimpleContext context = new SimpleContext();
Person person = new Person("John", "Doe");
context.setVariable("person", factory.createValueExpression(person, Person.class));
// create the expression
String expr = "My name is ${person.firstName} ${person.lastName}";
ValueExpression e = factory.createValueExpression(context, expr, String.class);
// evaluate the expression
System.out.println(e.getValue(context));
which prints 'My name is John Doe'
note that it's also possible to use an expression like this: '${firstName}' instead of '${person.firstName}', but then you will have to write and provide a custom resolver (javax.el.ELResolver) for the variable and property resolution
(My other answer's probably only useful if you're already using struts.)
Similar to sdb's answer, there is apache JEXL.
The UnifiedJEXL class provides template-like functionality, so you can write (as shown in javadocs):
JexlEngine jexl = new JexlEngine();
UnifiedJEXL ujexl = new UnifiedJEXL(jexl);
UnifiedJEXL.Expression expr = ujexl.parse("Hello ${user}");
String hello = expr.evaluate(context, expr).toString();
(The expr not only looks strange being passed as a parameter to a method on itself, but is indeed not needed as a parameter)
The context setup is shown earlier in the same page:
// Create a context and add data
JexlContext jc = new MapContext();
jc.set("foo", new Foo() );
You'll also need either commons-logging, or you can configure JEXL to use your own logger.
So to get close to what you asked, you can create:
public class Formatter {
public static String format(String format, Object ... inputs) {
JexlContext context = new MapContext();
for (int i=0;i<inputs.length;i++) {
context.set("_" + (i+1), inputs[i] );
}
JexlEngine jexl = new JexlEngine();
UnifiedJEXL ujexl = new UnifiedJEXL(jexl);
UnifiedJEXL.Expression expr = ujexl.parse(format);
return expr.evaluate(context).toString();
}
}
and call it with
String someString = "Your value is ${_1.myValue}.";
String result = Formatter.format(someString, new MyClass());
At which point, result is "Your value is foo."
It's in theory possible with a stackbased parser to determine the valueholders in the string, in combination with reflection (or better, a Javabean inspection API, such as Commons BeanUtils) to get the bean property values.
Unfortunately no ready-made nor 3rd party API comes to mind, if you were looking for that. It's an interesting question however.
You could create one with struts2/xwork/OGNL, similar to the below (copied from an email from Vlad)
public static String translateOgnl(String message, Map<Object, Object> args) {
OgnlValueStack stack = new OgnlValueStack();
stack.push(args);
return TextParseUtil.translateVariables(message, stack);
}
The javadocs for TextParseUtil.translateVariables() say
Converts all instances of ${...} in expression to the value returned by a call to ValueStack.findValue(java.lang.String). If an item cannot be found on the stack (null is returned), then the entire variable ${...} is not displayed, just as if the item was on the stack but returned an empty string.