ScriptJava

Java REPL today

There are a lot of benefits for a programming language to have a REPL. It helps one learn and explore the language features, gives ability to execute fast a code in question without launching IDE or modifiying existing project.

Writing whole Java code in command line seems like an overkill. Creating a class, then main method, then call to System.out.print() to execute such simple as Integer.MAX_VALUE command seems like a long way. What's why ScriptJava is not completely Java REPL. For example, semicolons(;) are mostly optional. There are a lot of build-ins methods, that can save a coder a few keyboard strokes. So, yeah, to know the value of Integer.MAX_VALUE you just input Integer.MAX_VALUE.

Build-in functions

• bool() -> inspired by python's function. In short: null, 0, or ""(empty string) returns false. Defined in Bool.java
• len() - > inspired by python's function. Unifies calls to get length of different objects. Defined in Length.java
• str() - > returns good object representation as a String. Defined in Str.java. In case of a file (if exists) returns file contents as a String
• print() > do as expected. Accepts multiple objects: print(1, 2, 3, 4). Every object's string representation will be obtained via str() call
• printf() -> Helper method to call System.out.printf(). Won't change the objects representation
• list() -> creates a list from supplied arguments, list(1, 2, 3, 4)
• map() -> original signature of this method is a bit scary: map(String[] keys, Object[] values), but with the help of the substitution command becomes more friendly: map(key1: 1, key2: 2)
• bin() -> returns binary representation of an integer value
• hex() -> return hex representation of an integer value
• date() -> helper method to call new Date()
• now() -> helper method to call System.currentTimeMillis()
• exec() -> executes supplied command as a String in a different process, returns String (the process output): exec("java -version")
• file() -> this method has different signatures. Called without parameters returns current execution folder. Called with a String as a parameter -> constructs File object with specified path
• del() -> removes file, takes a File object or a path
• write() -> takes a File object and it's contents as a String. Will write contents to a file
• json() -> Super primitive json parser that returns Element with the following methods: key(String) -> retrieves an JSON object by the key; at(int) -> retrieves a value from JSON array at give index; get() -> returns JSON primitive. Please note that exception will be thrown if method called on wrong JSON type (for example at will be called on JSON object)
• get() -> executes GET http request, returns response as a String
• post() -> executes POST http request, returns response as a String
• range() -> creates a range of integers to be easily interated, for (int i: range(10)). Returns int[]. has 3 signatures: range(end), range(start, end), range(start, end, step)
• dict() -> returns object's meta info (class name, parent class name, implements), fields and values. Has ability to return also info about methods
• type() -> returns human readable Type info (redirects call to str())
• toMap() -> converts an object into a Map<String, Object> (no recursive calls)
• fromMap() -> constructs an object from supplied Map<String, Object>
• set() -> tries to modify objects field given the name and value. Can modify final fields
• ni() -> simple call for Class.newInstance()
• store() -> stores a variable between script recompilations (actually can be useful only when removing previously retrieved value with ret call)
• ret() -> retirievs previously stored valiable or tries to obtain it if not present
• copy() -> copies supplied argument to the system clipboard and returns the value unmodified. copy(exec("echo HelloThere | cowsay -e --")) will copy result value of the exec call and print it.

Also, by default java.util.Math is statically imported, so pow(), sin(), cos(), etc are available

Special commands

• import -> adds an import statement for a script, for example import java.text.*
• clean -> completely cleans script
• quit -> exits from REPL
• bytecode -> prints bytecode for current script (if javap is present in PATH)

Substitutions

• map(key1: 1, key2: 2, key3: "some string") this (invalid in Java syntax) will be substituted new a call to build-in function map: map(new String[] { "key1", "key2", "key3" }, new Object[] { 1, 2, "some string" })
• ret("key", someCommand()) -> will be sustituted with: ret("key", new Provider() { Object provide() { return someCommand(); } }). This is done to skip initialization command if value is already defined, else the Provider object will be called to retrieve the value

Default imports

Except build-in functions these packages are imported by default:

• java.util.*
• java.text.*
• java.io.*

Custom libraries

Right now if there is a folder called libs inside execution directory, all jars that are inside it will be added to the script class path. Anyway you still need to import desired class first (here is no surprices).

Drawbacks

As we cannot achive completely scripting behavior from Java, there are certain things to be aware of. First, everytime you hit Enter the whole script is compiled from scratch. That's why all the variables will be set anew. For example:

Date d = date() // hit Enter
d // will print the *current* date, not the date value, that we obtained earlier

There is a woraround for this: build-in function ret:

Date d = ret("d", date())
d // will print the first obtained value

Installation

Before launching the executable make sure, that there is javac in the system PATH. Most likely that you already have it there. Also, if you wish to use bytecode function (that prints Java bytecode of compiled script) make sure that there is also a javap in the PATH.

Building

The main project has no dependencies, so it's a straight-forward process. However, building from IDE (when project is created from the source code) won't work, as current functionality requires the project's jar in the execution directory (due to build-in imports & IScript)

Tests require Gson (for json testing)

License

  Copyright 2016 Dimitry Ivanov (cr@dimitryivanov.ru)

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.