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     

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     

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     

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     

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     

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     

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);
    }
}