Java进阶：SE6调用编译器的两种方法[2]

三从内存中编译

JavaCompiler不仅可以编译硬盘上的Java文件而且还可以编译内存中的Java代码然后使用reflection来运行它们我们可以编写一个JavaSourceFromString类通过这个类可以输入Java源代码一但建立这个对象你可以向其中输入任意的Java代码然后编译和运行而且无需向硬盘上写class文件

import javalangreflect*;

import javaio*;

import javaxtools*;

import javaxtoolsJavaCompilerCompilationTask;

import javautil*;

import javanet*;

public class test_compilerapi

{

private static void compilerJava() throws Exception

{

JavaCompiler compiler = ToolProvidergetSystemJavaCompiler();

DiagnosticCollector diagnostics = new DiagnosticCollector();

// 定义一个StringWriter类用于写Java程序

StringWriter writer = new StringWriter();

PrintWriter out = new PrintWriter(writer);

// 开始写Java程序

outprintln(public class HelloWorld {);

outprintln( public static void main(String args[]) {);

outprintln( Systemoutprintln(\Hello World\););

outprintln( });

outprintln(});

outclose();

//为这段代码取个名子HelloWorld以便以后使用reflection调用

JavaFileObject file = new JavaSourceFromString(HelloWorld writertoString());

Iterable compilationUnits = ArraysasList(file);

JavaCompilerCompilationTask task = compilergetTask(null null

diagnostics null null compilationUnits);

boolean success = taskcall();

Systemoutprintln(Success: + success);

// 如果成功通过reflection执行这段Java程序

if (success)

{

Systemoutprintln(输出);

ClassforName(HelloWorld)getDeclaredMethod(main new Class[]

{ String[]class })invoke(null new Object[]

{ null });

Systemoutprintln(输出 );

}

}

public static void main(String args[]) throws Exception

{

compilerJava();

}

}

// 用于传递源程序的JavaSourceFromString类

class JavaSourceFromString extends SimpleJavaFileObject

{

final String code;

JavaSourceFromString(String name String code)

{

super(URIcreate(string:/// + namereplace( /)+ KindSOURCEextension) KindSOURCE);

thiscode = code;

}

@Override

public CharSequence getCharContent(boolean ignoreEncodingErrors)

{

return code;

}

}

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