Example of using the Google Closure Compiler at runtime

ClosureMinifier.java

/*
 * 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();
  }

}