Using Groovy in Java for custom expression resolution

As a jvm-based language, groovy is increasing in popularity. This article demonstrates how the Groovy.lang.Script class, inherited by GdK, supports custom expression parsing in a Java class.

Input:

Represents a map structure for a row of data. In practical applications, the most common scenario in which this structure is generated may be access to the database through JDBC, a result set of rows obtained by invoking the WebService service, and so on.

Target setting:

Suppose we want to perform an operation on the input data. In the example here, we simulate the most commonly used NVL function in Oracle.

Processing process:
First, define your own expression resolution class by inheriting Groovy.lang.Script:

public class Mybasicscript extends Script

　　

Implement specific parsing methods in this class:

public static object Nvl (Object Str,object val) {  return Str==null | | "". Equals (str)? Val:str;}

Second, instantiate a Compilerconfiguration object based on the above custom class.

Compilerconfiguration cfg = new compilerconfiguration (); Cfg.setscriptbaseclass (MyBasicScript.class.getName ());

　　

Instantiate a Groovyshell object with this compilerconfiguration instance as a parameter

Shell = new Groovyshell (CFG);

　　

Parses and runs an expression through a Shell object. Before running, you can bind script runtime context data through the Bingding object:

Binding binding = new binding (map); Script script = Shell.parse (expr); script.setbinding (binding); Script.run ();

　　

Complete code example (two classes, custom script implementation classes, calls, and test classes, respectively)

Package Jg.groovy;import Groovy.lang.script;import Java.lang.reflect.method;public class Mybasicscript extends Script  

　　

Package Jg.groovy;import Groovy.lang.binding;import Groovy.lang.groovyshell;import groovy.lang.script;import Java.util.hashmap;import Java.util.hashtable;import Java.util.map;import Org.codehaus.groovy.control.compilerconfiguration;public class Exprsupport {private static final Object lock = new Object ();p rivate static final Groovyshell shell;private static hashtable<string, script> cache = new Hashtable<s Tring, script> (); static {compilerconfiguration cfg = new compilerconfiguration (); Cfg.setscriptbaseclass ( MyBasicScript.class.getName ()); Shell = new Groovyshell (CFG);} public static Object parseexpr (String expr) {Script s = getscriptfromcache (expr); return S.run ();} public static Object parseexpr (String expr, map<?,? > map) {Binding binding = new binding (map); Script script = Getscriptfromcache (expr); script.setbinding (binding); return Script.run ();} private static Script Getscriptfromcache (String expr) {if (Cache.contains (expr)) {return cache.get (expr);} Synchronized (lock){if (Cache.contains (expr)) {return cache.get (expr);} Script script = Shell.parse (expr); Cache.put (expr, script); return script;}} /** * @param args */public static void main (string[] args) {//eg. get one row from dbmap<string, object> row = new Hashmap<string, Object> (), Row.put ("id", "" "), Row.put (" name "," ");//Call mode with bound data parameter System.out.println ( Exprsupport.parseexpr ("NVL (id,0)", Row)); System.out.println (exprsupport.parseexpr ("NVL (name, ' Anonymous ')", row)), or the call method without the binding data parameter, This is groovy's built-in capability System.out.println (exprsupport.parseexpr ("1+2"));}}

　　

Output:

42anonymous3

Summary: Combined with Groovy's built-in support for expressions and custom scripting capabilities, you can implement powerful expression parsing capabilities.

Using Groovy in Java for custom expression resolution