Is there any way to programmatically generate java class from a template?

I need a library or method to generate a java class (just generating source code of class as text format, no need to run or use it) from a template text file.

as an example I have a class template

package packagename.name.ab开发者_开发问答c;

import lib.sub.sub;

import lib.sub.sub2;

public class templateClass {

    public String getTemplateText() {
    //some operations here.
    }

    PlaceController getPlaceController() {
    //some operations here.
    }

}

and I want to add an library import, a function import and a parameter or line addition to template and add template to a project. //OPERATIONS

after import operations the code will be like :

package packagename.name.abc;

import lib.sub.sub; 
import lib.sub.sub2;
import NEWLIB.NEWSUB.NEWSUB;                 // NEW LIBRARY

public class templateClass {

    public String getTemplateText(String PARAMETER ) { // NEW PARAMETER
    //some operations here.
    String NEW_LINE = "";                // NEW LINE
    }

    PlaceController getPlaceController() {
    //some operations here.
    }

    public String getNEWText() {             //NEW FUNCTION
    //some operations here.
    }

}

I searched some libraries for this operations FreeMarker and ApacheVelocity are recomended for some similar problems. But I dont exactly understand the how to do this operation with FreeMarker. I think It's more likely have a usage as Tag Library ( like JSTL) I don't want to use template keywords in code (like $(temp) ) just functions "doImport", "addFunction", "addParameterToFunction" etc. Is it possible with this libraries or can anybody send some examples with about this operations?

In effect, you want to modify an arbitrary piece of code, in arbitrary ways.

To do this in a general way, you pretty much need to be able to parse the text so that you can place structures in the appropriate structured places. A template as normally used is just text; there is no structure to hang your hat on.

The most reliable way to do this is to use a source-to-source program transformation system. Such a tool allows you to explicitly state, "If you see this, then replace it by that". To accomplish your purpose, you'd say something like, "If you see a set of class declarations in class X, then add this class", generally stated as

  a rewritesto b if condition c

The DMS Software Reengineering Toolkit is a program transformation tool that will read source code, build compiler data structures (ASTs, symbol tables, flow graphs), allow you to apply source-to-source rewrites to the code represented as those structures, using source patterns to match/replace, and then regenerate valid source from the result.

DMS has parser/prettyprinters for many languages, including Java (1.4/1.5/1.6), C, C++, C#, COBOL, PHP, JavaScript, ...

For your add-a-parameter task, with DMS you would write the following transformation rule:

add_string_parameter(r:result_type,m:IDENTIFIER,p:parameter_list):
    method_signature->method_signature
=  " \r \m ( \p ) " -> " \r \m ( \p , String PARAMETER ) " if m="getTemplateText";

(-> corresponds to "rewritesto") This recognizes only method signatures (by searching the AST, not the raw text). The quote marks are meta-quotes containing your target language fragments, and are need to differentiate target-language text from rule-language text. r, m, p are metavariables that must match specific structures as given the the signature of the rule; \r \m \p are meta escapes in the target text saying that these structure must be present. The left hand side " \r \m ( \p ) " matches signatures and binds r, m, p to the AST structures support it; the right hand side specifies a replace in which the bound values of r, m, p are substittued to get the replacmement. The conditional "if" is there to insist the only the desired method gets modified; you might need a more complex condition if you have a big pile of code and want to hit just a specific method in it.

Will this help? - JET templates