Package bsh

Class Interpreter

  • All Implemented Interfaces:
    ConsoleInterface, Serializable, Runnable
    public class Interpreter
extends Object
implements Runnable, ConsoleInterface, Serializable
    The BeanShell script interpreter. An instance of Interpreter can be used to source scripts and evaluate statements or expressions.

    Here are some examples: 

                    Interpeter bsh = new Interpreter();

                // Evaluate statements and expressions
                bsh.eval("foo=Math.sin(0.5)");
                bsh.eval("bar=foo*5; bar=Math.cos(bar);");
                bsh.eval("for(i=0; i<10; i++) { print(\"hello\"); }");
                // same as above using java syntax and apis only
                bsh.eval("for(int i=0; i<10; i++) { System.out.println(\"hello\"); }");

                // Source from files or streams
                bsh.source("myscript.bsh");  // or bsh.eval("source(\"myscript.bsh\")");

                // Use set() and get() to pass objects in and out of variables
                bsh.set( "date", new Date() );
                Date date = (Date)bsh.get( "date" );
                // This would also work:
                Date date = (Date)bsh.eval( "date" );

                bsh.eval("year = date.getYear()");
                Integer year = (Integer)bsh.get("year");  // primitives use wrappers

                // With Java1.3+ scripts can implement arbitrary interfaces...
                // Script an awt event handler (or source it from a file, more likely)
                bsh.eval( "actionPerformed( e ) { print( e ); }");
                // Get a reference to the script object (implementing the interface)
                ActionListener scriptedHandler = 
                        (ActionListener)bsh.eval("return (ActionListener)this");
                // Use the scripted event handler normally...
                new JButton.addActionListener( script );

    In the above examples we showed a single interpreter instance, however you may wish to use many instances, depending on the application and how you structure your scripts. Interpreter instances are very light weight to create, however if you are going to execute the same script repeatedly and require maximum performance you should consider scripting the code as a method and invoking the scripted method each time on the same interpreter instance (using eval()).

    See the BeanShell User's Manual for more information.

    See Also:
    Serialized Form

    • Field Detail

      • DEBUG

        public static boolean DEBUG

      • TRACE

        public static boolean TRACE

      • LOCALSCOPING

        public static boolean LOCALSCOPING

      • evalOnly

        protected boolean evalOnly

      • interactive

        protected boolean interactive

    • Constructor Detail

      • Interpreter

        public Interpreter​(Reader in,
                   PrintStream out,
                   PrintStream err,
                   boolean interactive,
                   NameSpace namespace,
                   Interpreter parent,
                   String sourceFileInfo)
        The main constructor. All constructors should now pass through here.
        Parameters:
        namespace - If namespace is non-null then this interpreter's root namespace will be set to the one provided. If it is null a new one will be created for it.
        parent - The parent interpreter if this interpreter is a child of another. May be null. Children share a BshClassManager with their parent instance.
        sourceFileInfo - An informative string holding the filename or other description of the source from which this interpreter is reading... used for debugging. May be null.

      • Interpreter

        public Interpreter​(ConsoleInterface console,
                   NameSpace globalNameSpace)
        Construct a new interactive interpreter attached to the specified console using the specified parent namespace.

      • Interpreter

        public Interpreter​(ConsoleInterface console)
        Construct a new interactive interpreter attached to the specified console.

      • Interpreter

        public Interpreter()
        Create an interpreter for evaluation only.

    • Method Detail

      • setConsole

        public void setConsole​(ConsoleInterface console)
        Attach a console Note: this method is incomplete.

      • setNameSpace

        public void setNameSpace​(NameSpace globalNameSpace)
        Set the global namespace for this interpreter.

        Note: This is here for completeness. If you're using this a lot it may be an indication that you are doing more work than you have to. For example, caching the interpreter instance rather than the namespace should not add a significant overhead. No state other than the debug status is stored in the interpreter.

        All features of the namespace can also be accessed using the interpreter via eval() and the script variable 'this.namespace' (or global.namespace as necessary).

      • getNameSpace

        public NameSpace getNameSpace()
        Get the global namespace of this interpreter.

        Note: This is here for completeness. If you're using this a lot it may be an indication that you are doing more work than you have to. For example, caching the interpreter instance rather than the namespace should not add a significant overhead. No state other than the debug status is stored in the interpreter.

        All features of the namespace can also be accessed using the interpreter via eval() and the script variable 'this.namespace' (or global.namespace as necessary).

      • main

        public static void main​(String[] args)
        Run the text only interpreter on the command line or specify a file.

      • run

        public void run()
        Run interactively. (printing prompts, etc.)
        Specified by:
        run in interface Runnable

      • eval

        public Object eval​(Reader in,
                   NameSpace nameSpace,
                   String sourceFileInfo)
            throws EvalError
        Spawn a non-interactive local interpreter to evaluate text in the specified namespace. Return value is the evaluated object (or corresponding primitive wrapper).
        Parameters:
        sourceFileInfo - is for information purposes only. It is used to display error messages (and in the future may be made available to the script).
        Throws:
        EvalError - on script problems
        TargetError - on unhandled exceptions from the script

      • error

        public final void error​(Object o)
        Print an error message in a standard format on the output stream associated with this interpreter. On the GUI console this will appear in red, etc.
        Specified by:
        error in interface ConsoleInterface

      • getIn

        public Reader getIn()
        Get the input stream associated with this interpreter. This may be be stdin or the GUI console.
        Specified by:
        getIn in interface ConsoleInterface

      • getOut

        public PrintStream getOut()
        Get the outptut stream associated with this interpreter. This may be be stdout or the GUI console.
        Specified by:
        getOut in interface ConsoleInterface

      • getErr

        public PrintStream getErr()
        Get the error output stream associated with this interpreter. This may be be stderr or the GUI console.
        Specified by:
        getErr in interface ConsoleInterface

      • debug

        public static final void debug​(String s)
        Print a debug message on debug stream associated with this interpreter only if debugging is turned on.

      • get

        public Object get​(String name)
           throws EvalError
        Get the value of the name. name may be any value. e.g. a variable or field
        Throws:
        EvalError

      • set

        public void set​(String name,
                Object value)
         throws EvalError
        Assign the value to the name. name may evaluate to anything assignable. e.g. a variable or field.
        Throws:
        EvalError

      • unset

        public void unset​(String name)
           throws EvalError
        Unassign the variable name. Name should evaluate to a variable.
        Throws:
        EvalError

      • getInterface

        public Object getInterface​(Class interf)
                    throws EvalError
        Get a reference to the interpreter (global namespace), cast to the specified interface type. Assuming the appropriate methods of the interface are defined in the interpreter, then you may use this interface from Java, just like any other Java object.

        For example: 

                                Interpreter interpreter = new Interpreter();
                        // define a method called run()
                        interpreter.eval("run() { ... }");
                
                        // Fetch a reference to the interpreter as a Runnable
                        Runnable runnable = 
                                (Runnable)interpreter.getInterface( Runnable.class );

        Note that the interpreter does *not* require that any or all of the methods of the interface be defined at the time the interface is generated. However if you attempt to invoke one that is not defined you will get a runtime exception.

        Note also that this convenience method has exactly the same effect as evaluating the script: 

                                (Type)this;

        For example, the following is identical to the previous example: 

                                // Fetch a reference to the interpreter as a Runnable
                        Runnable runnable = 
                                (Runnable)interpreter.eval( "(Runnable)this" );

        Version requirement Although standard Java interface types are always available, to be used with arbitrary interfaces this feature requires that you are using Java 1.3 or greater.

        Throws:
        EvalError - if the interface cannot be generated because the version of Java does not support the proxy mechanism.

      • pathToFile

        public File pathToFile​(String fileName)
                throws IOException
        Localize a path to the file name based on the bsh.cwd interpreter working directory.
        Throws:
        IOException

      • redirectOutputToFile

        public static void redirectOutputToFile​(String filename)

      • setClassLoader

        public void setClassLoader​(ClassLoader externalCL)
        Set an external class loader to be used as the base classloader for BeanShell. The base classloader is used for all classloading unless/until the addClasspath()/setClasspath()/reloadClasses() commands are called to modify the interpreter's classpath. At that time the new paths /updated paths are added on top of the base classloader.

        BeanShell will use this at the same point it would otherwise use the plain Class.forName(). i.e. if no explicit classpath management is done from the script (addClassPath(), setClassPath(), reloadClasses()) then BeanShell will only use the supplied classloader. If additional classpath management is done then BeanShell will perform that in addition to the supplied external classloader. However BeanShell is not currently able to reload classes supplied through the external classloader.

        See Also:
        BshClassManager.setClassLoader( ClassLoader )

      • getClassManager

        public BshClassManager getClassManager()
        Get the class manager associated with this interpreter (the BshClassManager of this interpreter's global namespace). This is primarily a convenience method.

      • setStrictJava

        public void setStrictJava​(boolean b)
        Set strict Java mode on or off. This mode attempts to make BeanShell syntax behave as Java syntax, eliminating conveniences like loose variables, etc. When enabled, variables are required to be declared or initialized before use and method arguments are reqired to have types.

        This mode will become more strict in a future release when classes are interpreted and there is an alternative to scripting objects as method closures.

      • getSourceFileInfo

        public String getSourceFileInfo()
        Specify the source of the text from which this interpreter is reading. Note: there is a difference between what file the interrpeter is sourcing and from what file a method was originally parsed. One file may call a method sourced from another file. See SimpleNode for origination file info.
        See Also:
        SimpleNode.getSourceFile()

      • getParent

        public Interpreter getParent()
        Get the parent Interpreter of this interpreter, if any. Currently this relationship implies the following: 1) Parent and child share a BshClassManager 2) Children indicate the parent's source file information in error reporting. When created as part of a source() / eval() the child also shares the parent's namespace. But that is not necessary in general.

      • setExitOnEOF

        public void setExitOnEOF​(boolean value)
        Specify whether, in interactive mode, the interpreter exits Java upon end of input. If true, when in interactive mode the interpreter will issue a System.exit(0) upon eof. If false the interpreter no System.exit() will be done.

        Note: if you wish to cause an EOF externally you can try closing the input stream. This is not guaranteed to work in older versions of Java due to Java limitations, but should work in newer JDK/JREs. (That was the motivation for the Java NIO package).

      • setShowResults

        public void setShowResults​(boolean showResults)
        Turn on/off the verbose printing of results as for the show() command. If this interpreter has a parent the call is delegated. See the BeanShell show() command.

      • getShowResults

        public boolean getShowResults()
        Show on/off verbose printing status for the show() command. See the BeanShell show() command. If this interpreter has a parent the call is delegated.