Dumping a java object's properties
Is there a library that will recursively dump/print an objects properties? I'm looking for something similar to the console.dir() function in Firebug.
I'm aware of the commons-lang ReflectionToStringBuilder but it does not recurse into an object. I.e., if I run the following:
public class ToString {
public static void main(String [] args) {
System.out.println(ReflectionToStringBuilder.toString(new Outer(), ToStringStyle.MULTI_LINE_STYLE));
}
private static class Outer {
private int intValue = 5;
private Inner innerValue = new Inner();
}
private static class Inner {
private String stringValue = "foo";
}
}
I receive:
ToString$Outer@1b67f74[ intValue=5
innerValue=ToString$Inner@530daa ]
I realize that in my example, I could have overriden the toString() method for Inner but in the real world, I'm dealing with external objects that I can't modify.
Solution 1:
You could try XStream.
XStream xstream = new XStream(new Sun14ReflectionProvider(
new FieldDictionary(new ImmutableFieldKeySorter())),
new DomDriver("utf-8"));
System.out.println(xstream.toXML(new Outer()));
prints out:
<foo.ToString_-Outer>
<intValue>5</intValue>
<innerValue>
<stringValue>foo</stringValue>
</innerValue>
</foo.ToString_-Outer>
You could also output in JSON
And be careful of circular references ;)
Solution 2:
I tried using XStream as originally suggested, but it turns out the object graph I wanted to dump included a reference back to the XStream marshaller itself, which it didn't take too kindly to (why it must throw an exception rather than ignoring it or logging a nice warning, I'm not sure.)
I then tried out the code from user519500 above but found I needed a few tweaks. Here's a class you can roll into a project that offers the following extra features:
- Can control max recursion depth
- Can limit array elements output
- Can ignore any list of classes, fields, or class+field combinations - just pass an array with any combination of class names, classname+fieldname pairs separated with a colon, or fieldnames with a colon prefix ie:
[<classname>][:<fieldname>] - Will not output the same object twice (the output indicates when an object was previously visited and provides the hashcode for correlation) - this avoids circular references causing problems
You can call this using one of the two methods below:
String dump = Dumper.dump(myObject);
String dump = Dumper.dump(myObject, maxDepth, maxArrayElements, ignoreList);
As mentioned above, you need to be careful of stack-overflows with this, so use the max recursion depth facility to minimise the risk.
Hopefully somebody will find this useful!
package com.mycompany.myproject;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.util.HashMap;
public class Dumper {
private static Dumper instance = new Dumper();
protected static Dumper getInstance() {
return instance;
}
class DumpContext {
int maxDepth = 0;
int maxArrayElements = 0;
int callCount = 0;
HashMap<String, String> ignoreList = new HashMap<String, String>();
HashMap<Object, Integer> visited = new HashMap<Object, Integer>();
}
public static String dump(Object o) {
return dump(o, 0, 0, null);
}
public static String dump(Object o, int maxDepth, int maxArrayElements, String[] ignoreList) {
DumpContext ctx = Dumper.getInstance().new DumpContext();
ctx.maxDepth = maxDepth;
ctx.maxArrayElements = maxArrayElements;
if (ignoreList != null) {
for (int i = 0; i < Array.getLength(ignoreList); i++) {
int colonIdx = ignoreList[i].indexOf(':');
if (colonIdx == -1)
ignoreList[i] = ignoreList[i] + ":";
ctx.ignoreList.put(ignoreList[i], ignoreList[i]);
}
}
return dump(o, ctx);
}
protected static String dump(Object o, DumpContext ctx) {
if (o == null) {
return "<null>";
}
ctx.callCount++;
StringBuffer tabs = new StringBuffer();
for (int k = 0; k < ctx.callCount; k++) {
tabs.append("\t");
}
StringBuffer buffer = new StringBuffer();
Class oClass = o.getClass();
String oSimpleName = getSimpleNameWithoutArrayQualifier(oClass);
if (ctx.ignoreList.get(oSimpleName + ":") != null)
return "<Ignored>";
if (oClass.isArray()) {
buffer.append("\n");
buffer.append(tabs.toString().substring(1));
buffer.append("[\n");
int rowCount = ctx.maxArrayElements == 0 ? Array.getLength(o) : Math.min(ctx.maxArrayElements, Array.getLength(o));
for (int i = 0; i < rowCount; i++) {
buffer.append(tabs.toString());
try {
Object value = Array.get(o, i);
buffer.append(dumpValue(value, ctx));
} catch (Exception e) {
buffer.append(e.getMessage());
}
if (i < Array.getLength(o) - 1)
buffer.append(",");
buffer.append("\n");
}
if (rowCount < Array.getLength(o)) {
buffer.append(tabs.toString());
buffer.append(Array.getLength(o) - rowCount + " more array elements...");
buffer.append("\n");
}
buffer.append(tabs.toString().substring(1));
buffer.append("]");
} else {
buffer.append("\n");
buffer.append(tabs.toString().substring(1));
buffer.append("{\n");
buffer.append(tabs.toString());
buffer.append("hashCode: " + o.hashCode());
buffer.append("\n");
while (oClass != null && oClass != Object.class) {
Field[] fields = oClass.getDeclaredFields();
if (ctx.ignoreList.get(oClass.getSimpleName()) == null) {
if (oClass != o.getClass()) {
buffer.append(tabs.toString().substring(1));
buffer.append(" Inherited from superclass " + oSimpleName + ":\n");
}
for (int i = 0; i < fields.length; i++) {
String fSimpleName = getSimpleNameWithoutArrayQualifier(fields[i].getType());
String fName = fields[i].getName();
fields[i].setAccessible(true);
buffer.append(tabs.toString());
buffer.append(fName + "(" + fSimpleName + ")");
buffer.append("=");
if (ctx.ignoreList.get(":" + fName) == null &&
ctx.ignoreList.get(fSimpleName + ":" + fName) == null &&
ctx.ignoreList.get(fSimpleName + ":") == null) {
try {
Object value = fields[i].get(o);
buffer.append(dumpValue(value, ctx));
} catch (Exception e) {
buffer.append(e.getMessage());
}
buffer.append("\n");
}
else {
buffer.append("<Ignored>");
buffer.append("\n");
}
}
oClass = oClass.getSuperclass();
oSimpleName = oClass.getSimpleName();
}
else {
oClass = null;
oSimpleName = "";
}
}
buffer.append(tabs.toString().substring(1));
buffer.append("}");
}
ctx.callCount--;
return buffer.toString();
}
protected static String dumpValue(Object value, DumpContext ctx) {
if (value == null) {
return "<null>";
}
if (value.getClass().isPrimitive() ||
value.getClass() == java.lang.Short.class ||
value.getClass() == java.lang.Long.class ||
value.getClass() == java.lang.String.class ||
value.getClass() == java.lang.Integer.class ||
value.getClass() == java.lang.Float.class ||
value.getClass() == java.lang.Byte.class ||
value.getClass() == java.lang.Character.class ||
value.getClass() == java.lang.Double.class ||
value.getClass() == java.lang.Boolean.class ||
value.getClass() == java.util.Date.class ||
value.getClass().isEnum()) {
return value.toString();
} else {
Integer visitedIndex = ctx.visited.get(value);
if (visitedIndex == null) {
ctx.visited.put(value, ctx.callCount);
if (ctx.maxDepth == 0 || ctx.callCount < ctx.maxDepth) {
return dump(value, ctx);
}
else {
return "<Reached max recursion depth>";
}
}
else {
return "<Previously visited - see hashCode " + value.hashCode() + ">";
}
}
}
private static String getSimpleNameWithoutArrayQualifier(Class clazz) {
String simpleName = clazz.getSimpleName();
int indexOfBracket = simpleName.indexOf('[');
if (indexOfBracket != -1)
return simpleName.substring(0, indexOfBracket);
return simpleName;
}
}
Solution 3:
You can use ReflectionToStringBuilder with a custom ToStringStyle, for example:
class MyStyle extends ToStringStyle {
private final static ToStringStyle instance = new MyStyle();
public MyStyle() {
setArrayContentDetail(true);
setUseShortClassName(true);
setUseClassName(false);
setUseIdentityHashCode(false);
setFieldSeparator(", " + SystemUtils.LINE_SEPARATOR + " ");
}
public static ToStringStyle getInstance() {
return instance;
};
@Override
public void appendDetail(StringBuffer buffer, String fieldName, Object value) {
if (!value.getClass().getName().startsWith("java")) {
buffer.append(ReflectionToStringBuilder.toString(value, instance));
} else {
super.appendDetail(buffer, fieldName, value);
}
}
@Override
public void appendDetail(StringBuffer buffer, String fieldName, Collection value) {
appendDetail(buffer, fieldName, value.toArray());
}
}
And then you invoke it like:
ReflectionToStringBuilder.toString(value, MyStyle.getInstance());
Beware of circular references though!
You can also use json-lib (http://json-lib.sourceforge.net) and just do:
JSONObject.fromObject(value);
Solution 4:
this will print out all fields (including arrays of objects) of an object.
Fixed version of Ben Williams post from this thread
Note: this method uses recursion so If you have a very deep object graph you may get a stack-overflow (no pun intended ;) IF so you need to use the VM parameter -Xss10m. If your using eclipse put it in run>runconfiguration>augments (tab) VM augment box and press apply
import java.lang.reflect.Array;
import java.lang.reflect.Field;
public static String dump(Object o) {
StringBuffer buffer = new StringBuffer();
Class oClass = o.getClass();
if (oClass.isArray()) {
buffer.append("Array: ");
buffer.append("[");
for (int i = 0; i < Array.getLength(o); i++) {
Object value = Array.get(o, i);
if (value.getClass().isPrimitive() ||
value.getClass() == java.lang.Long.class ||
value.getClass() == java.lang.Integer.class ||
value.getClass() == java.lang.Boolean.class ||
value.getClass() == java.lang.String.class ||
value.getClass() == java.lang.Double.class ||
value.getClass() == java.lang.Short.class ||
value.getClass() == java.lang.Byte.class
) {
buffer.append(value);
if(i != (Array.getLength(o)-1)) buffer.append(",");
} else {
buffer.append(dump(value));
}
}
buffer.append("]\n");
} else {
buffer.append("Class: " + oClass.getName());
buffer.append("{\n");
while (oClass != null) {
Field[] fields = oClass.getDeclaredFields();
for (int i = 0; i < fields.length; i++) {
fields[i].setAccessible(true);
buffer.append(fields[i].getName());
buffer.append("=");
try {
Object value = fields[i].get(o);
if (value != null) {
if (value.getClass().isPrimitive() ||
value.getClass() == java.lang.Long.class ||
value.getClass() == java.lang.String.class ||
value.getClass() == java.lang.Integer.class ||
value.getClass() == java.lang.Boolean.class ||
value.getClass() == java.lang.Double.class ||
value.getClass() == java.lang.Short.class ||
value.getClass() == java.lang.Byte.class
) {
buffer.append(value);
} else {
buffer.append(dump(value));
}
}
} catch (IllegalAccessException e) {
buffer.append(e.getMessage());
}
buffer.append("\n");
}
oClass = oClass.getSuperclass();
}
buffer.append("}\n");
}
return buffer.toString();
}