JAVA很適合開發應用系統，但是數學建模和計算能力非其所長，如果該系統需要進行大量的統計或者優化的計算，調用R是一種很好的方式。JAVA負責系統的構建，R用來做運算引擎，從而實現應用型和分析性相結合的系統。

Rserve方式

Rserve作為一個package發布在CRAN上，可以直接使用install.packages("Rserve")進行安裝。需要使用時在R控制臺下加載該包，然后輸入命令Rserve()，開啟服務器，就可以供客戶端調用。

客戶端，下載REngine.jar和RserveEngine.jar兩個文件。

啟動"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，通過調用R的動態鏈接庫從而利用R中的函數。通過install.packages("rJava")安裝rJava就行，在安裝文件夾中，可以看到一個jri的子文件夾，里面有自帶的例子可以用來測試。

配置環境變量：

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.rn
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");    }}