JAVA很适合开发应用系统，但是数学建模和计算能力非其所长，如果该系统需要进行大量的统计或者优化的计算，调用R是一种很好的方式。JAVA负责系统的构建，R用来做运算引擎，从而实现应用型和分析性相结合的系统。
Rserve方式
Rserve作为一个package发布在CRAN上，可以直接使用install.packages("Rserve")进行安装。需要使用时在R控制台下加载该包，然后输入命令Rserve()，开启服务器，就可以供客户端调用。
客户端，下载REngine.jar和RserveEngine.jar两个文件。
启动"Rserve"
import org.rosuda.REngine.REXP;
import org.rosuda.REngine.Rserve.RConnection; public class RserveHandler { /**
* Application entry point.
*/
public static void main(String[] args) {
try {
RConnection conn = new RConnection();
REXP ex = conn.eval("R.version.string");
System.out.println(ex.asString());
} catch (Exception e) {
e.printStackTrace();
}
}
}
JRI方式
Java/R Interface，通过调用R的动态链接库从而利用R中的函数。通过install.packages("rJava")安装rJava就行，在安装文件夹中，可以看到一个jri的子文件夹，里面有自带的例子可以用来测试。
配置环境变量：
PATH .;%JAVA_HOME%\bin;%M2_HOME%\bin;%R_HOME%\bin\x64;%R_HOME%\library\rJava\jri\x64
package com.nsecn.rns; import java.awt.FileDialog;
import java.awt.Frame;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Enumeration; import org.rosuda.JRI.REXP;
import org.rosuda.JRI.RList;
import org.rosuda.JRI.RMainLoopCallbacks;
import org.rosuda.JRI.RVector;
import org.rosuda.JRI.Rengine; class TextConsole implements RMainLoopCallbacks { public void rWriteConsole(Rengine re, String text, int oType) {
System.out.print(text);
} public void rBusy(Rengine re, int which) {
System.out.println("rBusy(" + which + ")");
} public String rReadConsole(Rengine re, String prompt, int addToHistory) {
System.out.print(prompt);
try {
BufferedReader br = new BufferedReader(new InputStreamReader(
System.in));
String s = br.readLine();
return (s == null || s.length() == 0) ? s : s + "\n";
} catch (Exception e) {
System.out.println("jriReadConsole exception: " + e.getMessage());
}
return null;
} public void rShowMessage(Rengine re, String message) {
System.out.println("rShowMessage \"" + message + "\"");
} @SuppressWarnings("deprecation")
public String rChooseFile(Rengine re, int newFile) {
FileDialog fd = new FileDialog(new Frame(),
(newFile == 0) ? "Select a file" : "Select a new file",
(newFile == 0) ? FileDialog.LOAD : FileDialog.SAVE);
fd.show();
String res = null;
if (fd.getDirectory() != null)
res = fd.getDirectory();
if (fd.getFile() != null)
res = (res == null) ? fd.getFile() : (res + fd.getFile());
return res;
} public void rFlushConsole(Rengine re) {
} public void rLoadHistory(Rengine re, String filename) {
} public void rSaveHistory(Rengine re, String filename) {
}
} public class JIRunit { /**
* Application entry point.
*/
public static void main(String[] args) {
// just making sure we have the right version of everything
if (!Rengine.versionCheck()) {
System.err.println("** Version mismatch - Java files don't match library version.");
System.exit(1);
}
System.out.println("Creating Rengine (with arguments)");
// 1) we pass the arguments from the command line
// 2) we won't use the main loop at first, we'll start it later
// (that's the "false" as second argument)
// 3) the callbacks are implemented by the TextConsole class above
Rengine re = new Rengine(args, false, new TextConsole());
System.out.println("Rengine created, waiting for R");
// the engine creates R is a new thread, so we should wait until it's
// ready
if (!re.waitForR()) {
System.out.println("Cannot load R");
return;
} /*
* High-level API - do not use RNI methods unless there is no other way
* to accomplish what you want
*/
try {
REXP x;
re.eval("data(iris)", false);
System.out.println(x = re.eval("iris"));
// generic vectors are RVector to accomodate names
RVector v = x.asVector();
if (v.getNames() != null) {
System.out.println("has names:");
for (Enumeration<?> e = v.getNames().elements(); e
.hasMoreElements();) {
System.out.println(e.nextElement());
}
}
// for compatibility with Rserve we allow casting of vectors to
// lists
RList vl = x.asList();
String[] k = vl.keys();
if (k != null) {
System.out.println("and once again from the list:");
int i = 0;
while (i < k.length)
System.out.println(k[i++]);
} // get boolean array
System.out.println(x = re.eval("iris[[1]]>mean(iris[[1]])"));
// R knows about TRUE/FALSE/NA, so we cannot use boolean[] this way
// instead, we use int[] which is more convenient (and what R uses
// internally anyway)
int[] bi = x.asIntArray();
{
int i = 0;
while (i < bi.length) {
System.out.print(bi[i] == 0 ? "F " : (bi[i] == 1 ? "T " : "NA "));
i++;
}
System.out.println("");
} // push a boolean array
boolean by[] = { true, false, false };
re.assign("bool", by);
System.out.println(x = re.eval("bool"));
// asBool returns the first element of the array as RBool
// (mostly useful for boolean arrays of the length 1). is should
// return true
System.out.println("isTRUE? " + x.asBool().isTRUE()); // now for a real dotted-pair list:
System.out.println(x = re.eval("pairlist(a=1,b='foo',c=1:5)"));
RList l = x.asList();
if (l != null) {
int i = 0;
String[] a = l.keys();
System.out.println("Keys:");
while (i < a.length) {
System.out.println(a[i++]);
}
System.out.println("Contents:");
i = 0;
while (i < a.length) {
System.out.println(l.at(i++));
}
}
System.out.println(re.eval("sqrt(36)"));
} catch (Exception e) {
System.out.println("EX:" + e);
e.printStackTrace();
} // Part 2 - low-level API - for illustration purposes only!
// System.exit(0); // simple assignment like a<-"hello" (env=0 means use R_GlobalEnv)
long xp1 = re.rniPutString("hello");
re.rniAssign("a", xp1, 0); // Example: how to create a named list or data.frame
double da[] = { 1.2, 2.3, 4.5 };
double db[] = { 1.4, 2.6, 4.2 };
long xp3 = re.rniPutDoubleArray(da);
long xp4 = re.rniPutDoubleArray(db); // now build a list (generic vector is how that's called in R)
long la[] = { xp3, xp4 };
long xp5 = re.rniPutVector(la); // now let's add names
String sa[] = { "a", "b" };
long xp2 = re.rniPutStringArray(sa);
re.rniSetAttr(xp5, "names", xp2); // ok, we have a proper list now
// we could use assign and then eval "b<-data.frame(b)", but for now
// let's build it by hand:
String rn[] = { "1", "2", "3" };
long xp7 = re.rniPutStringArray(rn);
re.rniSetAttr(xp5, "row.names", xp7); long xp6 = re.rniPutString("data.frame");
re.rniSetAttr(xp5, "class", xp6); // assign the whole thing to the "b" variable
re.rniAssign("b", xp5, 0); {
System.out.println("Parsing");
long e = re.rniParse("data(iris)", 1);
System.out.println("Result = " + e + ", running eval");
long r = re.rniEval(e, 0);
System.out.println("Result = " + r + ", building REXP");
REXP x = new REXP(re, r);
System.out.println("REXP result = " + x);
} {
System.out.println("Parsing");
long e = re.rniParse("iris", 1);
System.out.println("Result = " + e + ", running eval");
long r = re.rniEval(e, 0);
System.out.println("Result = " + r + ", building REXP");
REXP x = new REXP(re, r);
System.out.println("REXP result = " + x);
} {
System.out.println("Parsing");
long e = re.rniParse("names(iris)", 1);
System.out.println("Result = " + e + ", running eval");
long r = re.rniEval(e, 0);
System.out.println("Result = " + r + ", building REXP");
REXP x = new REXP(re, r);
System.out.println("REXP result = " + x);
String s[] = x.asStringArray();
if (s != null) {
int i = 0;
while (i < s.length) {
System.out.println("[" + i + "] \"" + s[i] + "\"");
i++;
}
}
} {
System.out.println("Parsing");
long e = re.rniParse("rnorm(10)", 1);
System.out.println("Result = " + e + ", running eval");
long r = re.rniEval(e, 0);
System.out.println("Result = " + r + ", building REXP");
REXP x = new REXP(re, r);
System.out.println("REXP result = " + x);
double d[] = x.asDoubleArray();
if (d != null) {
int i = 0;
while (i < d.length) {
System.out.print(((i == 0) ? "" : ", ") + d[i]);
i++;
}
System.out.println("");
}
System.out.println("");
} {
REXP x = re.eval("1:10");
System.out.println("REXP result = " + x);
int d[] = x.asIntArray();
if (d != null) {
int i = 0;
while (i < d.length) {
System.out.print(((i == 0) ? "" : ", ") + d[i]);
i++;
}
System.out.println("");
}
} re.eval("print(1:10/3)"); boolean flag = true;
if (flag) {
// so far we used R as a computational slave without REPL
// now we start the loop, so the user can use the console
System.out.println("Now the console is yours ... have fun");
re.startMainLoop();
} else {
re.end();
System.out.println("end");
}
}
}
package com.nsecn.rns; import java.awt.Dimension;
import java.awt.FileDialog;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintStream; import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea; import org.rosuda.JRI.RConsoleOutputStream;
import org.rosuda.JRI.RMainLoopCallbacks;
import org.rosuda.JRI.Rengine; class TextConsole2 implements RMainLoopCallbacks { JFrame frame; public JTextArea textarea = new JTextArea(); @SuppressWarnings("deprecation")
public TextConsole2() {
frame = new JFrame();
frame.getContentPane().add(new JScrollPane(textarea));
frame.setSize(new Dimension(800, 600));
frame.show();
} public void rWriteConsole(Rengine re, String text, int oType) {
textarea.append(text);
} public void rBusy(Rengine re, int which) {
System.out.println("rBusy(" + which + ")");
} public String rReadConsole(Rengine re, String prompt, int addToHistory) {
System.out.print(prompt);
try {
BufferedReader br = new BufferedReader(new InputStreamReader(
System.in));
String s = br.readLine();
return (s == null || s.length() == 0) ? s : s + "\n";
} catch (Exception e) {
System.out.println("jriReadConsole exception: " + e.getMessage());
}
return null;
} public void rShowMessage(Rengine re, String message) {
System.out.println("rShowMessage \"" + message + "\"");
} @SuppressWarnings("deprecation")
public String rChooseFile(Rengine re, int newFile) {
FileDialog fd = new FileDialog(frame, (newFile == 0) ? "Select a file"
: "Select a new file", (newFile == 0) ? FileDialog.LOAD
: FileDialog.SAVE);
fd.show();
String res = null;
if (fd.getDirectory() != null)
res = fd.getDirectory();
if (fd.getFile() != null)
res = (res == null) ? fd.getFile() : (res + fd.getFile());
return res;
} public void rFlushConsole(Rengine re) {
} public void rLoadHistory(Rengine re, String filename) {
} public void rSaveHistory(Rengine re, String filename) {
}
} public class JRIano { /**
* Application entry point.
*/
public static void main(String[] args) { System.out.println("Press <Enter> to continue (time to attach the debugger if necessary)");
try {
System.in.read();
} catch (Exception e) {
} System.out.println("Creating Rengine (with arguments)");
Rengine re = new Rengine(args, true, new TextConsole2());
System.out.println("Rengine created, waiting for R");
if (!re.waitForR()) {
System.out.println("Cannot load R");
return;
} System.out.println("re-routing stdout/err into R console");
System.setOut(new PrintStream(new RConsoleOutputStream(re, 0)));
System.setErr(new PrintStream(new RConsoleOutputStream(re, 1))); System.out.println("Letting go; use main loop from now on");
}
}
