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https://github.com/EsotericSoftware/reflectasm

High performance Java reflection
https://github.com/EsotericSoftware/reflectasm

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High performance Java reflection

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README 

        
![](https://raw.github.com/wiki/EsotericSoftware/reflectasm/images/logo.png)



[![Build Status](https://travis-ci.org/EsotericSoftware/reflectasm.png?branch=master)](https://travis-ci.org/EsotericSoftware/reflectasm)

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Please use the [ReflectASM discussion group](http://groups.google.com/group/reflectasm-users) for support.



## Overview



ReflectASM is a very small Java library that provides high performance reflection by using code generation. An access class is generated to set/get fields, call methods, or create a new instance. The access class uses bytecode rather than Java's reflection, so it is much faster. It can also access primitive fields via bytecode to avoid boxing.



## Performance



![](http://chart.apis.google.com/chart?chma=100&chtt=Field%20Set/Get&chs=700x62&chd=t:1402081,11339107&chds=0,11339107&chxl=0:|Java%20Reflection|FieldAccess&cht=bhg&chbh=10&chxt=y&chco=6600FF)



![](http://chart.apis.google.com/chart?chma=100&chtt=Method%20Call&chs=700x62&chd=t:97390,208750&chds=0,208750&chxl=0:|Java%20Reflection|MethodAccess&cht=bhg&chbh=10&chxt=y&chco=6600AA)



![](http://chart.apis.google.com/chart?chma=100&chtt=Constructor&chs=700x62&chd=t:2853063,5828993&chds=0,5828993&chxl=0:|Java%20Reflection|ConstructorAccess&cht=bhg&chbh=10&chxt=y&chco=660066)



The source code for these benchmarks is included in the project. The above charts were generated on Oracle's Java 7u3, server VM.



## Installation



To use reflectasm with maven, please use the following snippet in your pom.xml



```xml

    

        com.esotericsoftware

        reflectasm

        1.11.9

    

```



## Usage



Method reflection with ReflectASM:



```java

SomeClass someObject = ...

MethodAccess access = MethodAccess.get(SomeClass.class);

access.invoke(someObject, "setName", "Awesome McLovin");

String name = (String)access.invoke(someObject, "getName");

```



Field reflection with ReflectASM:



```java

SomeClass someObject = ...

FieldAccess access = FieldAccess.get(SomeClass.class);

access.set(someObject, "name", "Awesome McLovin");

String name = (String)access.get(someObject, "name");

```



Constructor reflection with ReflectASM:



```java

ConstructorAccess access = ConstructorAccess.get(SomeClass.class);

SomeClass someObject = access.newInstance();

```



## Avoiding Name Lookup



For maximum performance when methods or fields are accessed repeatedly, the method or field index should be used instead of the name:



```java

SomeClass someObject = ...

MethodAccess access = MethodAccess.get(SomeClass.class);

int addNameIndex = access.getIndex("addName");

for (String name : names)

    access.invoke(someObject, addNameIndex, "Awesome McLovin");

```



Iterate all fields:



```java

FieldAccess access = FieldAccess.get(SomeClass.class);

for(int i = 0, n = access.getFieldCount(); i < n; i++) {

    access.set(instanceObject, i, valueToPut);              

}

```



## Visibility



ReflectASM can always access public members. An attempt is made to define access classes in the same classloader (using setAccessible) and package as the accessed class. If the security manager allows setAccessible to succeed, then protected and default access (package private) members can be accessed. If setAccessible fails, no exception is thrown, but only public members can be accessed. Private members can never be accessed.



## Exceptions



Stack traces when using ReflectASM are a bit cleaner. Here is Java's reflection calling a method that throws a RuntimeException:



```

Exception in thread "main" java.lang.reflect.InvocationTargetException

	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

	at java.lang.reflect.Method.invoke(Method.java:597)

	at com.example.SomeCallingCode.doit(SomeCallingCode.java:22)

Caused by: java.lang.RuntimeException

	at com.example.SomeClass.someMethod(SomeClass.java:48)

	... 5 more

```



Here is the same but when ReflectASM is used:



```

Exception in thread "main" java.lang.RuntimeException

	at com.example.SomeClass.someMethod(SomeClass.java:48)

	at com.example.SomeClassMethodAccess.invoke(Unknown Source)

	at com.example.SomeCallingCode.doit(SomeCallingCode.java:22)

```



If ReflectASM is used to invoke code that throws a checked exception, the checked exception is thrown. Because it is a compilation error to use try/catch with a checked exception around code that doesn't declare that exception as being thrown, you must catch Exception if you care about catching a checked exception in code you invoke with ReflectASM.