21 Aug 2008 @ 12:09 AM 
 

Java compiler API, compiling made easy

 


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Before Java 1.6 was released to the public I used the Runtime class (found in java.lang) to call the java compiler (javac.exe) directly to compile a Java file from another Java application, the line of code that i used looks like this

PLAIN TEXT
JAVA:
  1. Runtime.getRuntime().exec("C:\\WINDOWS\\system32\\cmd.exe /c start javac " +  userDir + "\\test\\"+className + ".java");

But luckily for me Java 1.6 introduced a handy utility that makes it possible to compile a Java application within a Java application without making direct calls to an external application. To demonstrate that I wrote a HelloWorld Java file and a CompilerConsoleDemo class that compiles the HelloWorld java file.

PLAIN TEXT
JAVA:
  1. public class HelloWorld {
  2. public static void main(String[] args){
  3. System.out.println("Hello World");
  4. }
  5. }

I wrote the Java code below to compile the above code like this

PLAIN TEXT
JAVA:
  1. /*--------------------------------------------------------------------------
  2. CompilerConsoleDemo class
  3. *****************
  4. By: HappyFace   http://www.engineeringserver.com - http://www.javaforums.net
  5. Contact:        info [@] engineeringserver.com
  6. Version:        20/August/2008
  7. Last updated:   20/August/2008
  8. *****************
  9. Note: a demo that uses the Compiler API from Java SE 1.6
  10. //----------------------------------------------------------------------*/
  11. import java.io.File;
  12. import java.io.FileNotFoundException;
  13. import java.io.FileOutputStream;
  14. import java.io.FileReader;
  15. import java.io.OutputStream;
  16. import java.util.Scanner;
  17.  
  18. import javax.tools.JavaCompiler;
  19. import javax.tools.ToolProvider;
  20.  
  21. public class CompilerConsoleDemo{
  22. static String userDir = System.getProperty("user.dir");
  23. String errOutput =userDir + "out.txt";
  25. Scanner sc;
  26. int lines = 1;
  27. String input = null;
  28.  
  29. public static void main(String[] args){
  30. CompilerConsoleDemo CD = new CompilerConsoleDemo(userDir + "\\HelloWorld.java");
  31. System.out.println("Compiling:");
  32. CD.showCode();
  33. System.out.println();
  34. System.out.println("Result(s):");
  35. CD.CompileCode();
  36. }
  37.  
  38. public CompilerConsoleDemo(String input){
  39. this.input = input;
  40. }
  41.  
  42. public void showCode(){
  43. String readCode;
  44. lines= 1;
  45. File f = new File(input);
  46. try {
  47. sc = new Scanner(f);
  48. while(sc.hasNext()){
  49. readCode = sc.nextLine();
  50. System.out.println(lines + " " + readCode);
  51. lines++;
  52. }
  53. } catch (FileNotFoundException e) {
  54. e.printStackTrace();
  55. }
  56. }
  57. public void CompileCode(){
  58. lines = 1;
  59. try {
  60. OutputStream err = new FileOutputStream(errOutput);
  61. JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
  62. int result = compiler.run(null,null,err,input);
  63.  
  64. if(result == 0){
  65. System.out.println("File successfully compiled!");
  66. System.out.println("");
  67. System.out.println("Output:");
  68. HelloWorld hw = ( HelloWorld ) Class.forName( "HelloWorld" ).newInstance();
  69. hw.main(null);
  70.  
  71. }
  72. else{
  73. f = new FileReader(errOutput);
  74. sc = new Scanner(f);
  75. String readErr;
  76. while(sc.hasNext()){
  77. readErr = sc.nextLine();
  78. System.out.println(lines + " " + readErr);
  79. lines++;
  80. }
  81. }
  82. } catch (FileNotFoundException e) {
  83. e.printStackTrace();
  85. // TODO Auto-generated catch block
  86. e.printStackTrace();
  88. // TODO Auto-generated catch block
  89. e.printStackTrace();
  91. // TODO Auto-generated catch block
  92. e.printStackTrace();
  93. }
  94. }
  95. }

The output should look like this
Compiling:
1 public class HelloWorld {
2 public static void main(String[] args){
3 System.out.println("Hello World");
4 }
5 }

Result(s):
File successfully compiled!

Output:
Hello World

But if an error occurred this will be shown instead
Compiling:
1 public class HelloWorld {
2 public static void main(String[] args){
3 System.out.println("Hello World")
4 }
5 }

Result(s):
1 C:\Eclipseworkspace\Demo\HelloWorld.java:3: ';' expected
2 System.out.println("Hello World")
3 ^
4 1 error

It looks like a really powerful utility but I haven't looked into the JavaCompiler class that much myself so there are still things that I need to figure out about the Compiler API to make maximal use it.

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Tags Tags: , , ,
Categories: Java Posted By: HappyFace
Last Edit: 22 Nov 2008 @ 05 48 PM

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  1. Online Java Coding - CodeCall Programming Forum says:
    September 17, 2008 at 3:48 pm

    [...] will once i have the time to write a readme and license for it. However you can take a look here: Engineeringserver.com | Java compiler API, compiling made easy and here Engineeringserver.com | [ java file copy ] Java folder watching to combine both of my [...]

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