提出了以下草案方式：
我们创建一个类，使用占位符 type TemplateArgOne，并添加一个用于促进解析的注解：
@GenerateFrom(EndlessArray.class)
public class EndlessArray {
TemplateArgOne[] values;
int size = 0;
int capacity;
public EndlessArray() {
capacity = 10;
values = new TemplateArgOne[capacity];
}
public void reserve(int newcapacity ) {
if( newcapacity > capacity ) {
TemplateArgOne[] newvalues = new TemplateArgOne[newcapacity];
for( int i = 0; i < size; i++ ) {
newvalues[i] = values[i];
}
values = newvalues;
capacity = newcapacity;
}
}
public void add( TemplateArgOne value ) {
if( size >= capacity - 1 ) {
reserve( capacity * 2);
}
values[size] = value;
}
public void set( int i, TemplateArgOne value ) {
values[i] = value;
}
public TemplateArgOne get( int i ) {
return values[i];
}
}
我们将 TemplateArgOne 定义为一个空类，所以上面的代码编译得很好，可以在 Eclipse 中毫无问题地编辑它：
public class TemplateArgOne {
}
现在，我们创建一个新类来实例化模板类，并添加几个注释来告诉生成器我们要实例化哪个类，以及我们想要什么类型TemplateArgOne：
@GenerateFrom(root.javalanguage.realtemplates.EndlessArray.class)
@GenerateArg(from=TemplateArgOne.class,to=double.class)
public class EndlessArrayDouble {
}
然后我们运行生成器，传入我们的源代码目录，以及实例化类的名称，即EndlessArrayDouble：
public static void main(String[] args ) throws Exception {
new RealTemplateGenerator().go("/data/dev/machinelearning/MlPrototyping", EndlessArrayDouble.class);
}
快！当我们转到 EndlessArrayDouble 类时，它已经被我们的代码填充了！：
package root.javalanguage.realtemplates;
import root.javalanguage.realtemplates.RealTemplateGenerator.*;
@GenerateArg(from=TemplateArgOne.class,to=double.class)
@GenerateFrom(root.javalanguage.realtemplates.EndlessArray.class)
public class EndlessArrayDouble {
double[] values;
int size = 0;
int capacity;
public EndlessArrayDouble() {
capacity = 10;
values = new double[capacity];
}
public void reserve(int newcapacity ) {
if( newcapacity > capacity ) {
double[] newvalues = new double[newcapacity];
for( int i = 0; i < size; i++ ) {
newvalues[i] = values[i];
}
values = newvalues;
capacity = newcapacity;
}
}
public void add( double value ) {
if( size >= capacity - 1 ) {
reserve( capacity * 2);
}
values[size] = value;
}
public void set( int i, double value ) {
values[i] = value;
}
public double get( int i ) {
return values[i];
}
}
注意，如果多次运行，不修改模板类，那么实例化类java文件不会被修改，即不会触发Eclipse中的冗余文件重载。
生成器代码：
//Copyright Hugh Perkins 2012, hughperkins -at- gmail
//
//This Source Code Form is subject to the terms of the Mozilla Public License,
//v. 2.0. If a copy of the MPL was not distributed with this file, You can
//obtain one at http://mozilla.org/MPL/2.0/.
package root.javalanguage.realtemplates;
import java.lang.annotation.*;
import java.util.*;
public class RealTemplateGenerator {
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.SOURCE)
public @interface GenerateFrom {
Class<?> value();
}
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.SOURCE)
public @interface GenerateArg {
Class<?> from();
Class<?> to();
}
public final static BufferedReader newBufferedReader(String filepath ) throws Exception {
FileInputStream fileInputStream = new FileInputStream( filepath );
InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
return bufferedReader;
}
public final static BufferedWriter newBufferedWriter( String filepath ) throws Exception {
FileOutputStream fileOutputStream = new FileOutputStream(filepath);
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream);
BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter);
return bufferedWriter;
}
public final static ArrayList<String> readFileAsLines(String filepath ) throws Exception {
ArrayList<String> lines = new ArrayList<String>(40000);
BufferedReader bufferedReader = newBufferedReader(filepath);
String line = bufferedReader.readLine();
int numlines = 0;
while( line != null ) {
lines.add(line.substring(0, line.length() ));
line = bufferedReader.readLine();
numlines++;
}
bufferedReader.close();
return lines;
}
public final static void writeFileFromLines( String filepath, ArrayList<String> lines ) throws Exception {
BufferedWriter bufferedWriter = newBufferedWriter(filepath);
for( String line : lines ) {
bufferedWriter.write(line + "\n");
}
bufferedWriter.close();
}
void go( String sourcedirectory, Class<?> targetclass ) throws Exception {
String targetclassfilepath = sourcedirectory + "/" + targetclass.getCanonicalName().replace(".","/") + ".java";
ArrayList<String> initialLines = FileHelper.readFileAsLines(targetclassfilepath);
String fromclassname = "";
HashMap<String,String> argOldToNew = new HashMap<String, String>();
ArrayList<String> generatelines = new ArrayList<String>();
for( String line : initialLines ) {
if( line.startsWith("@GenerateFrom")){
fromclassname = line.split("\\(")[1].split("\\.class")[0];
}
if( line.startsWith("@GenerateArg")) {
String fromclass= line.split("from=")[1].split("\\.")[0];
String toclass = line.split("to=")[1].split("\\.")[0];
argOldToNew.put(fromclass,toclass);
generatelines.add(line);
}
}
Class<?> targettype = this.getClass().forName(fromclassname);
String fromclassfilepath = sourcedirectory + "/" + targettype.getCanonicalName().replace(".","/") + ".java";
ArrayList<String> templateLines = FileHelper.readFileAsLines(fromclassfilepath );
ArrayList<String> generatedLines = new ArrayList<String>();
for( int i = 0; i < templateLines.size(); i++ ){
String line = templateLines.get(i);
if( !line.startsWith("@GenerateFrom") && !line.startsWith("@GenerateArg")) {
for( String oldarg : argOldToNew.keySet() ) {
line = line.replace(oldarg, argOldToNew.get(oldarg));
}
line = line.replace(targettype.getSimpleName(), targetclass.getSimpleName());
} else if( line.startsWith("@GenerateFrom") ) {
for( String generateline : generatelines ) {
generatedLines.add(generateline);
}
}
generatedLines.add(line);
}
boolean isModified = false;
if( initialLines.size() != generatedLines.size() ) {
isModified = true;
} else {
for(int i = 0; i < initialLines.size(); i++ ) {
if( !initialLines.get(i).equals(generatedLines.get(i))) {
isModified = true;
break;
}
}
}
if( isModified ) {
FileHelper.writeFileFromLines(targetclassfilepath, generatedLines);
System.out.println("Generated " + targetclassfilepath );
} else {
System.out.println("No change to " + targetclassfilepath );
}
}
public static void main(String[] args ) throws Exception {
new RealTemplateGenerator().go("/data/dev/machinelearning/MlPrototyping", EndlessArrayDouble.class);
}
}