java内存动态编译执行

一般的java的动态编译是需要先生成java文件，然后编译成class，最后用classloader加载进来生成最终的实例的。 
本例程则不需要生成任何文件，一切在内存中进行。

 

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代码片段(6)[全屏查看所有代码]

1. [代码][Java]代码     

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package org.jui.core.dynamic;   public class DynaCompTest {      public static void main(String[] args) throws Exception {          String fullName = "DynaClass" ;          StringBuilder src = new StringBuilder();          src.append( "public class DynaClass {\n" );          src.append( "    public String toString() {\n" );          src.append( "        return \"Hello, I am \" + " );          src.append( "this.getClass().getSimpleName();\n" );          src.append( "    }\n" );          src.append( "}\n" );            System.out.println(src);          DynamicEngine de = DynamicEngine.getInstance();          Object instance =  de.javaCodeToObject(fullName,src.toString());          System.out.println(instance);      } }

2. [代码][Java]代码     

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package org.jui.core.dynamic;   import javax.tools.*; import java.util.ArrayList; import java.util.List; import java.util.Arrays; import java.net.URL; import java.net.URLClassLoader; import java.io.File;   public class DynamicEngine {      private static DynamicEngine ourInstance = new DynamicEngine();        public static DynamicEngine getInstance() {          return ourInstance;      }      private URLClassLoader parentClassLoader;      private String classpath;      private DynamicEngine() {          this .parentClassLoader = (URLClassLoader) this .getClass().getClassLoader();          this .buildClassPath();      }      private void buildClassPath() {          this .classpath = null ;          StringBuilder sb = new StringBuilder();          for (URL url : this .parentClassLoader.getURLs()) {              String p = url.getFile();              sb.append(p).append(File.pathSeparator);          }          this .classpath = sb.toString();      }      public Object javaCodeToObject(String fullClassName, String javaCode) throws IllegalAccessException, InstantiationException {          long start = System.currentTimeMillis();          Object instance = null ;          JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();          DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();          ClassFileManager fileManager = new ClassFileManager(compiler.getStandardFileManager(diagnostics, null , null ));            List<JavaFileObject> jfiles = new ArrayList<JavaFileObject>();          jfiles.add( new CharSequenceJavaFileObject(fullClassName, javaCode));            List<String> options = new ArrayList<String>();          options.add( "-encoding" );          options.add( "UTF-8" );          options.add( "-classpath" );          options.add( this .classpath);            JavaCompiler.CompilationTask task = compiler.getTask( null , fileManager, diagnostics, options, null , jfiles);          boolean success = task.call();            if (success) {              JavaClassObject jco = fileManager.getJavaClassObject();              DynamicClassLoader dynamicClassLoader = new DynamicClassLoader( this .parentClassLoader);              Class clazz = dynamicClassLoader.loadClass(fullClassName,jco);              instance = clazz.newInstance();          } else {              String error = "" ;              for (Diagnostic diagnostic : diagnostics.getDiagnostics()) {                  error = error + compilePrint(diagnostic);              }          }          long end = System.currentTimeMillis();          System.out.println( "javaCodeToObject use:" +(end-start)+ "ms" );          return instance;      }        private String compilePrint(Diagnostic diagnostic) {          System.out.println( "Code:" + diagnostic.getCode());          System.out.println( "Kind:" + diagnostic.getKind());          System.out.println( "Position:" + diagnostic.getPosition());          System.out.println( "Start Position:" + diagnostic.getStartPosition());          System.out.println( "End Position:" + diagnostic.getEndPosition());          System.out.println( "Source:" + diagnostic.getSource());          System.out.println( "Message:" + diagnostic.getMessage( null ));          System.out.println( "LineNumber:" + diagnostic.getLineNumber());          System.out.println( "ColumnNumber:" + diagnostic.getColumnNumber());          StringBuffer res = new StringBuffer();          res.append( "Code:[" + diagnostic.getCode() + "]\n" );          res.append( "Kind:[" + diagnostic.getKind() + "]\n" );          res.append( "Position:[" + diagnostic.getPosition() + "]\n" );          res.append( "Start Position:[" + diagnostic.getStartPosition() + "]\n" );          res.append( "End Position:[" + diagnostic.getEndPosition() + "]\n" );          res.append( "Source:[" + diagnostic.getSource() + "]\n" );          res.append( "Message:[" + diagnostic.getMessage( null ) + "]\n" );          res.append( "LineNumber:[" + diagnostic.getLineNumber() + "]\n" );          res.append( "ColumnNumber:[" + diagnostic.getColumnNumber() + "]\n" );          return res.toString();      } }

3. [代码][Java]代码     

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package org.jui.core.dynamic;   import javax.tools.JavaFileObject; import javax.tools.SimpleJavaFileObject; import java.net.URI;   public class CharSequenceJavaFileObject extends SimpleJavaFileObject {        private CharSequence content;          public CharSequenceJavaFileObject(String className,                                        CharSequence content) {          super (URI.create( "string:///" + className.replace( '.' , '/' )                  + JavaFileObject.Kind.SOURCE.extension), JavaFileObject.Kind.SOURCE);          this .content = content;      }        @Override      public CharSequence getCharContent(              boolean ignoreEncodingErrors) {          return content;      } }

4. [代码][Java]代码     

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package org.jui.core.dynamic;   import javax.tools.*; import java.io.IOException; import java.security.SecureClassLoader;   public class ClassFileManager extends          ForwardingJavaFileManager {      public JavaClassObject getJavaClassObject() {          return jclassObject;      }        private JavaClassObject jclassObject;          public ClassFileManager(StandardJavaFileManager          standardManager) {          super (standardManager);      }          @Override      public JavaFileObject getJavaFileForOutput(Location location,          String className, JavaFileObject.Kind kind, FileObject sibling)              throws IOException {              jclassObject = new JavaClassObject(className, kind);          return jclassObject;      } }

5. [代码][Java]代码     

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package org.jui.core.dynamic;   import javax.tools.JavaFileObject; import javax.tools.SimpleJavaFileObject; import java.io.IOException; import java.io.OutputStream; import java.io.ByteArrayOutputStream; import java.net.URI;   public class JavaClassObject extends SimpleJavaFileObject {        protected final ByteArrayOutputStream bos =          new ByteArrayOutputStream();          public JavaClassObject(String name, JavaFileObject.Kind kind) {          super (URI.create( "string:///" + name.replace( '.' , '/' )              + kind.extension), kind);      }          public byte [] getBytes() {          return bos.toByteArray();      }        @Override      public OutputStream openOutputStream() throws IOException {          return bos;      } }

6. [代码][Java]代码     

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package org.jui.core.dynamic;   import java.net.URLClassLoader; import java.net.URL;   public class DynamicClassLoader extends URLClassLoader {      public DynamicClassLoader(ClassLoader parent) {          super ( new URL[ 0 ], parent);      }        public Class findClassByClassName(String className) throws ClassNotFoundException {          return this .findClass(className);      }        public Class loadClass(String fullName, JavaClassObject jco) {          byte [] classData = jco.getBytes();          return this .defineClass(fullName, classData, 0 , classData.length);      } }