是否可以通过编程方式仅在内存中编译Java源代码？

Question

我找到了许多参考资料，它们解释了如何使用JavaCompiler该类以编程方式编译Java 类：

JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
int result = compiler.run(null, null, null, "a_file_name");

但是，我想知道是否有一个开放源代码库，可以让我编译以编程方式生成的源代码（因此不涉及src文件）并在输出流中生成一些字节代码（而不在文件系统中生成类文件）
）。

例如，我正在寻找能够写这样的东西：

InputStream input = generateSourceCode();
OutputStream output = getByteCode(input);
doCoolStuffWithByteCode(output);

谢谢你的帮助。

Answer 1

首先，请看JavaCompiler
API
。基本上：

1. 在字符串中创建Java类。
2. 将字符串放入扩展SimpleJavaFileObject的类中。
3. 使用JavaCompiler实例进行编译。

最后，将方法称为新类。

这是与JDK6
+一起使用的示例：

import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.reflect.InvocationTargetException;
import java.net.URI;
import java.util.Arrays;

import javax.tools.Diagnostic;
import javax.tools.DiagnosticCollector;
import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.SimpleJavaFileObject;
import javax.tools.ToolProvider;
import javax.tools.JavaCompiler.CompilationTask;
import javax.tools.JavaFileObject.Kind;

public class CompileSourceInMemory {
  public static void main(String args[]) throws IOException {
    JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
    DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();

    StringWriter writer = new StringWriter();
    PrintWriter out = new PrintWriter(writer);
    out.println("public class HelloWorld {");
    out.println("  public static void main(String args[]) {");
    out.println("    System.out.println(\"This is in another java file\");");    
    out.println("  }");
    out.println("}");
    out.close();
    JavaFileObject file = new JavaSourceFromString("HelloWorld", writer.toString());

    Iterable<? extends JavaFileObject> compilationUnits = Arrays.asList(file);
    CompilationTask task = compiler.getTask(null, null, diagnostics, null, null, compilationUnits);

    boolean success = task.call();
    for (Diagnostic diagnostic : diagnostics.getDiagnostics()) {
      System.out.println(diagnostic.getCode());
      System.out.println(diagnostic.getKind());
      System.out.println(diagnostic.getPosition());
      System.out.println(diagnostic.getStartPosition());
      System.out.println(diagnostic.getEndPosition());
      System.out.println(diagnostic.getSource());
      System.out.println(diagnostic.getMessage(null));

    }
    System.out.println("Success: " + success);

    if (success) {
      try {
        Class.forName("HelloWorld").getDeclaredMethod("main", new Class[] { String[].class })
            .invoke(null, new Object[] { null });
      } catch (ClassNotFoundException e) {
        System.err.println("Class not found: " + e);
      } catch (NoSuchMethodException e) {
        System.err.println("No such method: " + e);
      } catch (IllegalAccessException e) {
        System.err.println("Illegal access: " + e);
      } catch (InvocationTargetException e) {
        System.err.println("Invocation target: " + e);
      }
    }
  }
}

class JavaSourceFromString extends SimpleJavaFileObject {
  final String code;

  JavaSourceFromString(String name, String code) {
    super(URI.create("string:///" + name.replace('.','/') + Kind.SOURCE.extension),Kind.SOURCE);
    this.code = code;
  }

  @Override
  public CharSequence getCharContent(boolean ignoreEncodingErrors) {
    return code;
  }
}