blocks|key|2053241|text|试试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2053242|++++Dimension+d+=+new+Dimension(2,2);

++++String+expressionString+=+"width";
++++Object+expr+=+Ognl.parseExpression(expressionString);

++++OgnlContext+ctx+=+new+OgnlContext();
++++Object+value+=+Ognl.getValue(expr,+ctx,+d);

++++System.out.println("Value:+"+%2B+value);|code-block|syntax|javascript|2053243|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Try this:

<pre><code> Dimension d = new Dimension(2,2);

 String expressionString = "width";
 Object expr = Ognl.parseExpression(expressionString);

 OgnlContext ctx = new OgnlContext();
 Object value = Ognl.getValue(expr, ctx, d);

 System.out.println("Value: " + value);
</code></pre>

blocks|key|2053252|text|下面是jython+(编译成java的python)的helloworld示例。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2053253|from+ognl+import+Ognl,+OgnlContext
from+java.lang+import+String

exp+=+Ognl.parseExpression("substring(2,+5)")

print+Ognl.getValue(exp,+OgnlContext(),+String("abcdefghj"))|code-block|syntax|javascript|2053254|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Jython^0|3|6|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Here is an example helloworld for <a href="http://en.wikipedia.org/wiki/Jython" rel="nofollow noreferrer">jython</a> (python that compiles to java).

<pre><code>from ognl import Ognl, OgnlContext
from java.lang import String

exp = Ognl.parseExpression("substring(2, 5)")

print Ognl.getValue(exp, OgnlContext(), String("abcdefghj"))
</code></pre>

blocks|key|2053381|text|如果只想从对象中读取属性，那么PropertyUtils.getProperty+(来自commons-beanutils)就足够了。然而，如果目的是评估条件句之类的，那么Ognl可能会受益。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2053382|下面是带有布尔值的相同的Dimension示例：|2053383|Dimension+d+=+new+Dimension();
d.setSize(100,200)+;//+width+and+height

Map<String,Object>+map+=+new+HashMap<String,Object>();
map.put("dimension",+d);

String+expression+=+"dimension.width+==+100+&&+dimension.height+==+200";
Object+exp+=+Ognl.parseExpression(expression);
Boolean+b+=+(Boolean)+Ognl.getValue(exp,map);
//+b+would+evaluate+to+true+in+this+case|code-block|syntax|javascript|2053384|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

If the intention is only to read properties from an object then PropertyUtils.getProperty (from commons-beanutils) may suffice. However, if the intention is to evaluate conditionals and such, then Ognl may benefit.

Here is the same Dimension example with a boolean:

<pre><code>Dimension d = new Dimension();
d.setSize(100,200) ;// width and height

Map&lt;String,Object&gt; map = new HashMap&lt;String,Object&gt;();
map.put("dimension", d);

String expression = "dimension.width == 100 &amp;&amp; dimension.height == 200";
Object exp = Ognl.parseExpression(expression);
Boolean b = (Boolean) Ognl.getValue(exp,map);
// b would evaluate to true in this case
</code></pre>

blocks|key|2053399|text|OGNL允许您通过字符串表达式访问对象、字段和方法，当您失去了数据与其使用者之间的耦合架构时，这将变得非常有用。它在幕后使用反射，但与纯反射方法相比，它确实加快了开发速度。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2053400|一些一行的例子|2053401|System.out.println(Ognl.getValue("x",+new+Point(5,5)));
System.out.println(Ognl.getValue("size",+new+ArrayList<Object>()));|code-block|syntax|javascript|2053402|Documentation已经有了许多基本的和更高级的ognl表达式。|offset|length|2053403|entityMap|0|LINK|mutability|MUTABLE|url|http://commons.apache.org/proper/commons-ognl/language-guide.html^0|0|0|0|0|D|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|X|8|@]|9|@$K|Y|L|Z|1|10]]|A|$]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

OGNL allows you to access objects fields and methods via string expressions which becomes very useful when you have lose coupled architecture between data and it's consumers. It's using reflection under the hood but definitely speeds up development compared to a pure reflection approach. 

Some one line examples

<pre><code>System.out.println(Ognl.getValue("x", new Point(5,5)));
System.out.println(Ognl.getValue("size", new ArrayList&lt;Object&gt;()));
</code></pre>

<a href="http://commons.apache.org/proper/commons-ognl/language-guide.html" rel="nofollow">Documentation</a> already has a number of basic and more advanced ognl expressions.

I need to use OGNL for reading some properties from Java object. OGNL is completely new thing to me. The documentation available for OGNL is OGNL's website is really confusing to me.

So anyone can provide a simple <code>HelloWorld</code> example for using OGNL (or any link to a tutorial is also helpful).

OGNL Hello World in Java

Java

我需要使用OGNL从Java对象中读取一些属性。OGNL对我来说是一个全新的事物。OGNL的网站上提供的OGNL文档让我很困惑。所以任何人都可以提供一个简单的HelloWorld示例来使用OGNL (或者任何教程的链接也是很有帮助的)。

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