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SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.
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* Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
* Institute of Molecular Cell Biology and Genetics.
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* this list of conditions and the following disclaimer.
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package org.scijava.util;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.HashMap;
import java.util.StringTokenizer;
/**
* A general-purpose reflection wrapper class.
*
* Note: use of this class is discouraged in favor of compile-time (i.e.,
* type-safe) dependency linkages. However, there are times when it proves very
* useful for writing blocks of reflected code in a more succinct way than you
* can do with the vanilla {@link java.lang.reflect} API. Of course, debugging
* such reflected code becomes much more difficult—caveat emptor!
*
*
* @author Curtis Rueden
*/
public class ReflectedUniverse {
// -- Fields --
/** Hashtable containing all variables present in the universe. */
private final HashMap variables;
/** Class loader for imported classes. */
private final ClassLoader loader;
/** Whether to force our way past restrictive access modifiers. */
private boolean force;
// -- Constructors --
/** Constructs a new reflected universe. */
public ReflectedUniverse() {
this((ClassLoader) null);
}
/**
* Constructs a new reflected universe, with the given URLs representing
* additional search paths for imported classes (in addition to the
* CLASSPATH).
*/
public ReflectedUniverse(final URL[] urls) {
this(urls == null ? null : new URLClassLoader(urls));
}
/** Constructs a new reflected universe that uses the given class loader. */
public ReflectedUniverse(final ClassLoader loader) {
variables = new HashMap();
this.loader = loader == null ? getClass().getClassLoader() : loader;
}
// -- Utility methods --
/**
* Returns whether the given object is compatible with the specified class for
* the purposes of reflection.
*/
public static boolean isInstance(final Class c, final Object o) {
return (o == null || c.isInstance(o) ||
(c == byte.class && o instanceof Byte) ||
(c == short.class && o instanceof Short) ||
(c == int.class && o instanceof Integer) ||
(c == long.class && o instanceof Long) ||
(c == float.class && o instanceof Float) ||
(c == double.class && o instanceof Double) ||
(c == boolean.class && o instanceof Boolean) || (c == char.class && o instanceof Character));
}
// -- ReflectedUniverse API methods --
/**
* Executes a command in the universe. The following syntaxes are valid:
*
* - import fully.qualified.package.ClassName
* - var = new ClassName(param1, ..., paramN)
* - var.method(param1, ..., paramN)
* - var2 = var.method(param1, ..., paramN)
* - ClassName.method(param1, ..., paramN)
* - var2 = ClassName.method(param1, ..., paramN)
* - var2 = var
*
* Important guidelines:
*
* - Any referenced class must be imported first using "import".
* - Variables can be exported from the universe with getVar().
* - Variables can be imported to the universe with setVar().
* - Each parameter must be either:
*
* - a variable in the universe
* - a static or instance field (i.e., no nested methods)
* - a string literal (remember to escape the double quotes)
* - an integer literal
* - a long literal (ending in L)
* - a double literal (containing a decimal point)
* - a boolean literal (true or false)
* - the null keyword
*
*
*
*/
public Object exec(String command) throws ReflectException {
command = command.trim();
if (command.startsWith("import ")) {
// command is an import statement
command = command.substring(7).trim();
final int dot = command.lastIndexOf(".");
final String varName = dot < 0 ? command : command.substring(dot + 1);
Class c;
try {
c = Class.forName(command, true, loader);
}
catch (final NoClassDefFoundError err) {
throw new ReflectException("No such class: " + command, err);
}
catch (final ClassNotFoundException exc) {
throw new ReflectException("No such class: " + command, exc);
}
catch (final RuntimeException exc) {
// HACK: workaround for bug in Apache Axis2
final String msg = exc.getMessage();
if (msg != null && msg.indexOf("ClassNotFound") < 0) throw exc;
throw new ReflectException("No such class: " + command, exc);
}
setVar(varName, c);
return null;
}
// get variable where results of command should be stored
final int eqIndex = command.indexOf("=");
String target = null;
if (eqIndex >= 0) {
target = command.substring(0, eqIndex).trim();
command = command.substring(eqIndex + 1).trim();
}
Object result = null;
// parse parentheses
final int leftParen = command.indexOf("(");
if (leftParen < 0) {
// command is a simple assignment
result = getVar(command);
if (target != null) setVar(target, result);
return result;
}
else if (leftParen != command.lastIndexOf("(") ||
command.indexOf(")") != command.length() - 1)
{
throw new ReflectException("Invalid parentheses");
}
// parse arguments
final String arglist = command.substring(leftParen + 1);
final StringTokenizer st = new StringTokenizer(arglist, "(,)");
final int len = st.countTokens();
final Object[] args = new Object[len];
for (int i = 0; i < len; i++) {
final String arg = st.nextToken().trim();
args[i] = getVar(arg);
}
command = command.substring(0, leftParen);
if (command.startsWith("new ")) {
// command is a constructor call
final String className = command.substring(4).trim();
final Object var = getVar(className);
if (var == null) {
throw new ReflectException("Class not found: " + className);
}
else if (!(var instanceof Class)) {
throw new ReflectException("Not a class: " + className);
}
final Class cl = (Class) var;
// Search for a constructor that matches the arguments. Unfortunately,
// calling cl.getConstructor(argClasses) does not work, because
// getConstructor() is not flexible enough to detect when the arguments
// are subclasses of the constructor argument classes, making a brute
// force search through all public constructors necessary.
Constructor constructor = null;
final Constructor[] c = cl.getConstructors();
for (int i = 0; i < c.length; i++) {
if (force) c[i].setAccessible(true);
final Class[] params = c[i].getParameterTypes();
if (params.length == args.length) {
boolean match = true;
for (int j = 0; j < params.length; j++) {
if (!isInstance(params[j], args[j])) {
match = false;
break;
}
}
if (match) {
constructor = c[i];
break;
}
}
}
if (constructor == null) {
final StringBuffer sb = new StringBuffer(command);
for (int i = 0; i < args.length; i++) {
sb.append(i == 0 ? "(" : ", ");
sb.append(args[i].getClass().getName());
}
sb.append(")");
throw new ReflectException("No such constructor: " + sb.toString());
}
// invoke constructor
Exception exc = null;
try {
result = constructor.newInstance(args);
}
catch (final InstantiationException e) {
exc = e;
}
catch (final IllegalAccessException e) {
exc = e;
}
catch (final InvocationTargetException e) {
exc = e;
}
if (exc != null) {
throw new ReflectException("Cannot instantiate object", exc);
}
}
else {
// command is a method call
final int dot = command.indexOf(".");
if (dot < 0) throw new ReflectException("Syntax error");
final String varName = command.substring(0, dot).trim();
final String methodName = command.substring(dot + 1).trim();
final Object var = getVar(varName);
if (var == null) {
throw new ReflectException("No such variable: " + varName);
}
final Class varClass =
var instanceof Class ? (Class) var : var.getClass();
// Search for a method that matches the arguments. Unfortunately,
// calling varClass.getMethod(methodName, argClasses) does not work,
// because getMethod() is not flexible enough to detect when the
// arguments are subclasses of the method argument classes, making a
// brute force search through all public methods necessary.
Method method = null;
final Method[] m = varClass.getMethods();
for (int i = 0; i < m.length; i++) {
if (force) m[i].setAccessible(true);
if (methodName.equals(m[i].getName())) {
final Class[] params = m[i].getParameterTypes();
if (params.length == args.length) {
boolean match = true;
for (int j = 0; j < params.length; j++) {
if (!isInstance(params[j], args[j])) {
match = false;
break;
}
}
if (match) {
method = m[i];
break;
}
}
}
}
if (method == null) {
throw new ReflectException("No such method: " + methodName);
}
// invoke method
Exception exc = null;
try {
result = method.invoke(var, args);
}
catch (final IllegalAccessException e) {
exc = e;
}
catch (final InvocationTargetException e) {
exc = e;
}
if (exc != null) {
throw new ReflectException("Cannot execute method: " + methodName, exc);
}
}
// assign result to proper variable
if (target != null) setVar(target, result);
return result;
}
/** Registers a variable in the universe. */
public void setVar(final String varName, final Object obj) {
if (obj == null) variables.remove(varName);
else variables.put(varName, obj);
}
/** Registers a variable of primitive type boolean in the universe. */
public void setVar(final String varName, final boolean b) {
setVar(varName, new Boolean(b));
}
/** Registers a variable of primitive type byte in the universe. */
public void setVar(final String varName, final byte b) {
setVar(varName, new Byte(b));
}
/** Registers a variable of primitive type char in the universe. */
public void setVar(final String varName, final char c) {
setVar(varName, Character.valueOf(c));
}
/** Registers a variable of primitive type double in the universe. */
public void setVar(final String varName, final double d) {
setVar(varName, new Double(d));
}
/** Registers a variable of primitive type float in the universe. */
public void setVar(final String varName, final float f) {
setVar(varName, new Float(f));
}
/** Registers a variable of primitive type int in the universe. */
public void setVar(final String varName, final int i) {
setVar(varName, Integer.valueOf(i));
}
/** Registers a variable of primitive type long in the universe. */
public void setVar(final String varName, final long l) {
setVar(varName, Long.valueOf(l));
}
/** Registers a variable of primitive type short in the universe. */
public void setVar(final String varName, final short s) {
setVar(varName, Short.valueOf(s));
}
/**
* Returns the value of a variable or field in the universe. Primitive types
* will be wrapped in their Java Object wrapper classes.
*/
public Object getVar(final String varName) throws ReflectException {
if (varName.equals("null")) {
// variable is a null value
return null;
}
else if (varName.equals("true")) {
// variable is a boolean literal
return Boolean.TRUE;
}
else if (varName.equals("false")) {
// variable is a boolean literal
return Boolean.FALSE;
}
else if (varName.startsWith("\"") && varName.endsWith("\"")) {
// variable is a string literal
return varName.substring(1, varName.length() - 1);
}
try {
if (varName.matches("-?\\d+")) {
// variable is an int literal
return new Integer(varName);
}
else if (varName.matches("-?\\d+L")) {
// variable is a long literal
return new Long(varName);
}
else if (varName.matches("-?\\d*\\.\\d*")) {
// variable is a double literal
return new Double(varName);
}
}
catch (final NumberFormatException exc) {
throw new ReflectException("Invalid literal: " + varName, exc);
}
final int dot = varName.indexOf(".");
if (dot >= 0) {
// get field value of variable
final String className = varName.substring(0, dot).trim();
final Object var = variables.get(className);
if (var == null) {
throw new ReflectException("No such class: " + className);
}
final Class varClass =
var instanceof Class ? (Class) var : var.getClass();
final String fieldName = varName.substring(dot + 1).trim();
Field field;
try {
field = varClass.getField(fieldName);
if (force) field.setAccessible(true);
}
catch (final NoSuchFieldException exc) {
throw new ReflectException("No such field: " + varName, exc);
}
Object fieldVal;
try {
fieldVal = field.get(var);
}
catch (final IllegalAccessException exc) {
throw new ReflectException("Cannot get field value: " + varName, exc);
}
return fieldVal;
}
// get variable
final Object var = variables.get(varName);
return var;
}
/** Sets whether access modifiers (protected, private, etc.) are ignored. */
public void setAccessibilityIgnored(final boolean ignore) {
force = ignore;
}
/** Gets whether access modifiers (protected, private, etc.) are ignored. */
public boolean isAccessibilityIgnored() {
return force;
}
// -- Main method --
/**
* Allows exploration of a reflected universe in an interactive environment.
*/
public static void main(final String[] args) throws IOException {
final ReflectedUniverse r = new ReflectedUniverse();
System.out.println("Reflected universe test environment. "
+ "Type commands, or press ^D to quit.");
if (args.length > 0) {
r.setAccessibilityIgnored(true);
System.out.println("Ignoring accessibility modifiers.");
}
final BufferedReader in =
new BufferedReader(new InputStreamReader(System.in, "UTF-8"));
while (true) {
System.out.print("> ");
final String line = in.readLine();
if (line == null) break;
try {
r.exec(line);
}
catch (final ReflectException exc) {
System.err.println("Could not execute '" + line + "':");
exc.printStackTrace();
}
}
System.out.println();
}
}