ASM Sample Project (#2664)

* ASM Sample Project

* Update Premain.java

* Update pom.xml

asm/pom.xml

@@ -0,0 +1,51 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung.examples</groupId>
+    <artifactId>asm</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+    <dependencies>
+        <dependency>
+            <groupId>org.ow2.asm</groupId>
+            <artifactId>asm</artifactId>
+            <version>5.2</version>
+        </dependency>
+        <dependency>
+            <groupId>org.ow2.asm</groupId>
+            <artifactId>asm-util</artifactId>
+            <version>5.2</version>
+        </dependency>
+    </dependencies>
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+    </properties>
+    <build> 
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-jar-plugin</artifactId>
+                <version>2.4</version>
+                <configuration>
+                    <archive>
+                        <manifestEntries>
+                            <Premain-Class>
+                                com.baeldung.examples.asm.instrumentation.Premain
+                            </Premain-Class>
+                        </manifestEntries>
+                    </archive>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>2.9</version>
+                <configuration>
+                    <argLine>-javaagent:"C:\asm-1.0.jar"</argLine>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+</project>

asm/src/main/java/com/baeldung/examples/asm/CustomClassWriter.java

@@ -0,0 +1,160 @@
+package com.baeldung.examples.asm;
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.ClassWriter;
+import org.objectweb.asm.FieldVisitor;
+import org.objectweb.asm.MethodVisitor;
+import static org.objectweb.asm.Opcodes.ACC_PUBLIC;
+import static org.objectweb.asm.Opcodes.ACC_STATIC;
+import static org.objectweb.asm.Opcodes.ASM4;
+import static org.objectweb.asm.Opcodes.V1_5;
+import org.objectweb.asm.Type;
+import org.objectweb.asm.util.TraceClassVisitor;
+
+/**
+ *
+ * @author baeldung
+ * @param <String>
+ */
+public class CustomClassWriter {
+
+    ClassReader reader;
+    ClassWriter writer;
+    AddFieldAdapter addFieldAdapter;
+    AddInterfaceAdapter addInterfaceAdapter;
+    PublicizeMethodAdapter pubMethAdapter;
+    final static String CLASSNAME = "java.lang.Integer";
+    final static String CLONEABLE = "java/lang/Cloneable";
+
+    public CustomClassWriter() {
+
+        try {
+            reader = new ClassReader(CLASSNAME);
+            writer = new ClassWriter(reader, 0);
+
+        } catch (IOException ex) {
+            Logger.getLogger(CustomClassWriter.class.getName()).log(Level.SEVERE, null, ex);
+        }
+    }
+
+    public CustomClassWriter(byte[] contents) {
+        reader = new ClassReader(contents);
+        writer = new ClassWriter(reader, 0);
+    }
+
+    public static void main(String[] args) {
+        CustomClassWriter ccw = new CustomClassWriter();
+        ccw.publicizeMethod();
+    }
+
+    public byte[] addField() {
+        addFieldAdapter = new AddFieldAdapter("aNewBooleanField", org.objectweb.asm.Opcodes.ACC_PUBLIC, writer);
+        reader.accept(addFieldAdapter, 0);
+        return writer.toByteArray();
+    }
+
+    public byte[] publicizeMethod() {
+        pubMethAdapter = new PublicizeMethodAdapter(writer);
+        reader.accept(pubMethAdapter, 0);
+        return writer.toByteArray();
+    }
+
+    public byte[] addInterface() {
+        addInterfaceAdapter = new AddInterfaceAdapter(writer);
+        reader.accept(addInterfaceAdapter, 0);
+        return writer.toByteArray();
+    }
+
+    public class AddInterfaceAdapter extends ClassVisitor {
+
+        public AddInterfaceAdapter(ClassVisitor cv) {
+            super(ASM4, cv);
+        }
+
+        @Override
+        public void visit(int version, int access, String name,
+                String signature, String superName, String[] interfaces) {
+            String[] holding = new String[interfaces.length + 1];
+            holding[holding.length - 1] = CLONEABLE;
+            System.arraycopy(interfaces, 0, holding, 0, interfaces.length);
+
+            cv.visit(V1_5, access, name, signature, superName, holding);
+        }
+
+    }
+
+    public class PublicizeMethodAdapter extends ClassVisitor {
+
+        final Logger logger = Logger.getLogger("PublicizeMethodAdapter");
+        TraceClassVisitor tracer;
+        PrintWriter pw = new PrintWriter(System.out);
+
+        public PublicizeMethodAdapter(ClassVisitor cv) {
+            super(ASM4, cv);
+            this.cv = cv;
+            tracer = new TraceClassVisitor(cv, pw);
+        }
+
+        @Override
+        public MethodVisitor visitMethod(int access,
+                String name,
+                String desc,
+                String signature,
+                String[] exceptions) {
+
+            if (name.equals("toUnsignedString0")) {
+                logger.info("Visiting unsigned method");
+                return tracer.visitMethod(ACC_PUBLIC + ACC_STATIC, name, desc, signature, exceptions);
+            }
+            return tracer.visitMethod(access, name, desc, signature, exceptions);
+
+        }
+
+        public void visitEnd() {
+            tracer.visitEnd();
+            System.out.println(tracer.p.getText());
+        }
+
+    }
+
+    public class AddFieldAdapter extends ClassVisitor {
+
+        String fieldName;
+        int access;
+        boolean isFieldPresent;
+
+        public AddFieldAdapter(String fieldName, int access, ClassVisitor cv) {
+            super(ASM4, cv);
+            this.cv = cv;
+            this.access = access;
+            this.fieldName = fieldName;
+        }
+
+        @Override
+        public FieldVisitor visitField(int access, String name, String desc,
+                String signature, Object value) {
+            if (name.equals(fieldName)) {
+                isFieldPresent = true;
+            }
+            return cv.visitField(access, name, desc, signature, value);
+        }
+
+        @Override
+        public void visitEnd() {
+            if (!isFieldPresent) {
+                FieldVisitor fv = cv.visitField(access, fieldName, Type.BOOLEAN_TYPE.toString(), null, null);
+                if (fv != null) {
+                    fv.visitEnd();
+                }
+            }
+            cv.visitEnd();
+        }
+
+    }
+
+}

asm/src/main/java/com/baeldung/examples/asm/instrumentation/Premain.java

@@ -0,0 +1,32 @@
+package com.baeldung.examples.asm.instrumentation;
+
+import com.baeldung.examples.asm.CustomClassWriter;
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.IllegalClassFormatException;
+import java.lang.instrument.Instrumentation;
+import java.security.ProtectionDomain;
+
+/**
+ *
+ * @author baeldung
+ */
+public class Premain {
+
+    public static void premain(String agentArgs, Instrumentation inst) {
+        inst.addTransformer(new ClassFileTransformer() {
+
+            @Override
+            public byte[] transform(ClassLoader l, String name, Class c,
+                    ProtectionDomain d, byte[] b)
+                    throws IllegalClassFormatException {
+
+                if (name.equals("java/lang/Integer")) {
+                    CustomClassWriter cr = new CustomClassWriter(b);
+                    return cr.addField();
+                }
+                return b;
+            }
+        });
+    }
+
+}

pom.xml

@@ -28,6 +28,7 @@
     </properties>
 
     <modules>
+        <module>asm</module>     
         <module>atomix</module>
         <module>apache-cayenne</module>
         <module>aws</module>