Minifying Javascript at runtime

Steve Souders pointed at this today; I've done something similar in the past, but I struggled somewhat with the documentation. Hopefully this might be useful to others.

	/*
	* Copyright 2011 James Abley
	*
	* 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.
	*/
	import java.io.IOException;
	import java.io.Reader;
	import java.io.StringReader;
	import java.util.Arrays;
	import java.util.Collections;
	import java.util.List;
	import com.google.javascript.jscomp.CompilationLevel;
	import com.google.javascript.jscomp.CompilerOptions;
	import com.google.javascript.jscomp.JSSourceFile;
	import com.google.javascript.jscomp.Result;
	public class ClosureMinifier {
	private final Reader input;
	/**
	* @param stringReader
	*/
	public ClosureMinifier(Reader input) {
	this.input = input;
	}
	/**
	* @return
	*/
	public Reader minify() throws IOException {
	List<JSSourceFile> externs = Collections.emptyList();
	List<JSSourceFile> inputs = Arrays.asList(JSSourceFile.fromCode("default.js",
	getCodeFromReader()));
	CompilerOptions options = new CompilerOptions();
	CompilationLevel.SIMPLE_OPTIMIZATIONS.setOptionsForCompilationLevel(options);
	com.google.javascript.jscomp.Compiler compiler = new com.google.javascript.jscomp.Compiler();
	Result result = compiler.compile(externs, inputs, options);
	if (result.success) {
	return new StringReader(compiler.toSource());
	}
	throw new IllegalArgumentException("Unable to minify input source");
	}
	private String getCodeFromReader() throws IOException {
	StringBuilder sb = new StringBuilder(10240);
	int c;
	while ((c = this.input.read()) != -1) {
	sb.append((char) c);
	}
	return sb.toString();
	}
	}

view raw ClosureMinifier.java hosted with ❤ by GitHub

As part of a product that serves as a rendering runtime for mobile, this allows authors to create Javascript, and the runtime can optimise and cache on the fly. We like it!