io读取文件到String
public static String loadAFileToStringDE1(File f) throws IOException {
long beginTime = System.currentTimeMillis();
InputStream is = null;
String ret = null;
try {
is = new BufferedInputStream( new FileInputStream(f) );
long contentLength = f.length();
ByteArrayOutputStream outstream = new ByteArrayOutputStream( contentLength > 0 ? (int) contentLength : 1024);
byte[] buffer = new byte[4096];
int len;
while ((len = is.read(buffer)) > 0) {
outstream.write(buffer, 0, len);
}
outstream.close();
ret = outstream.toString();
//byte[] ba = outstream.toByteArray();
//ret = new String(ba);
} finally {
if(is!=null) {try{is.close();} catch(Exception e){} }
}
long endTime = System.currentTimeMillis();
System.out.println("方法1用时"+ (endTime-beginTime) + "ms");
return ret;
}
public static String loadAFileToStringDE2(File f) throws IOException {
long beginTime = System.currentTimeMillis();
InputStream is = null;
String ret = null;
try {
is = new FileInputStream(f) ;
long contentLength = f.length();
byte[] ba = new byte[(int)contentLength];
is.read(ba);
ret = new String(ba);
} finally {
if(is!=null) {try{is.close();} catch(Exception e){} }
}
long endTime = System.currentTimeMillis();
System.out.println("方法2用时"+ (endTime-beginTime) + "ms");
return ret;
}
public static String loadAFileToStringDE3(File f) throws IOException {
long beginTime = System.currentTimeMillis();
BufferedReader br = null;
String ret = null;
try {
br = new BufferedReader(new FileReader(f));
String line = null;
StringBuffer sb = new StringBuffer((int)f.length());
while( (line = br.readLine() ) != null ) {
sb.append(line).append(LINE_BREAK);
}
ret = sb.toString();
} finally {
if(br!=null) {try{br.close();} catch(Exception e){} }
}
long endTime = System.currentTimeMillis();
System.out.println("方法3用时"+ (endTime-beginTime) + "ms");
return ret;
}
3个方法去读取一个大于50M的文件，当不设置jvm参数时都OutofMemery，当设置-Xmx128M时。只有方法3 可以通过，设置到-Xmx256M时也只有方法3可以通过，干脆设置512M，都可以了，运行时间如果正常的话一般都在4～5S
