ASM DEMO

原文:http://caodaoxi.iteye.com/blog/723910
 
これはASMツールでStudentクラスにpublic Stringタイプのaddress属性を追加します。1属性を追加する必要があるオリジナルクラス：Student.java

public class Student {
    private int age;
    private String name;
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }   
} 

 2,プロパティを追加するアダプター：AddFieldAdapter.java

import org.objectweb.asm.ClassAdapter;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.FieldVisitor;

public class AddFieldAdapter extends ClassAdapter {
    private int accessModifier;
    private String name;
    private String desc;
    private boolean isFieldPresent;

    public AddFieldAdapter(ClassVisitor cv, int accessModifier, String name, String desc) {
        super(cv);
        this.accessModifier = accessModifier;
        this.name = name;
        this.desc = desc;
    }

    @Override
    public FieldVisitor visitField(int access, String name, String desc,
            String signature, Object value) {
        if (name.equals(this.name)) {
            isFieldPresent = true;
        }
        return cv.visitField(access, name, desc, signature, value);
    }

    @Override
    public void visitEnd() {
        if (!isFieldPresent) {
            FieldVisitor fv = cv.visitField(accessModifier, name, desc, null, null);
            if (fv != null) {
                fv.visitEnd();
            }
        }
        cv.visitEnd();
    }
} 

 3属性を追加するツールAddField.java

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import org.objectweb.asm.ClassAdapter;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.Opcodes;

public class AddField {

    private Class clazz = null;
    private ClassReader cr = null;
    private ClassWriter cw = null;
    private ClassAdapter ca = null;
    private File classFile = null;

    private final static String CLASS_FILE_SUFFIX = ".class";

    public AddField(Class clazz) {
        this.clazz = clazz;
    }

    /**
     *      public     
     * @param fieldName         
     * @param fieldDesc            
     */
    public void addPublicField(String fieldName, String fieldDesc) {
        if(cr == null) {
            try {
                cr = new ClassReader(clazz.getCanonicalName());
            } catch (IOException e) {
                e.printStackTrace();
            }
            cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS);
        }
        if(ca == null) {
            ca = new AddFieldAdapter(cw, Opcodes.ACC_PUBLIC, fieldName, fieldDesc);
        } else {
            ca = new AddFieldAdapter(ca, Opcodes.ACC_PUBLIC, fieldName, fieldDesc);
        }
    }

    /**
     *          .class   
     *
     */
    public void writeByteCode() {
        cr.accept(ca, ClassReader.SKIP_DEBUG);
        byte[] bys = cw.toByteArray();
        OutputStream os = null;
        try {
            os = new FileOutputStream(getFile());
            os.write(bys);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                os.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     *        File   
     * @return
     */
    private File getFile() {
        if(classFile == null) {
            StringBuffer sb = new StringBuffer();
            sb.append(clazz.getResource("/"))
                .append(clazz.getCanonicalName().replace(".", File.separator))
                .append(CLASS_FILE_SUFFIX);
            classFile = new File(sb.substring(6));
        }
        return classFile;
    }
} 

 4バイトコード処理：PreCompleProcess.java

public class PreCompileProcess {

    public static void main(String[] args) {

        //   Student     
        AddField add = new AddField(Student.class);

        //        address，    java.lang.String   public   
        add.addPublicField("address", "Ljava/lang/String;");

        //         tel，    int   public   
        add.addPublicField("tel", "I");

        //      .class   
        add.writeByteCode();
    }
} 

 5、テストクラス：Test.java

public class Test {

    public static void main(String[] args) {
        Student stu = new Student();
        stu.setAge(10);
        stu.setName("Tom");
        stu.address = "Beijing";    //      address   
        stu.tel = 56;               //      tel   
        System.out.println("Name:    " + stu.getName());
        System.out.println("Age:     " + stu.getAge());
        System.out.println("Address: " + stu.address);
        System.out.println("Tel:     " + stu.tel);
    }
} 

 上のコードはASMツールでコンパイルできます。ASMで行けます。http://asm.objectweb.org/ 上からダウンロードします実行順序：javac Student.java javac-cp.lib/asm-all-31.jar ProCompleProcess.java java-cp.lib/asm-all-3.1.jar ProCopileProcess javac Test.java java TestはStudent.javaで修正がない場合、PreCompleProcessは一回だけ実行すればいいです。